Malabsorption

Overview & Definition

Malabsorption is the impaired absorption of macronutrients (fat, carbohydrate, protein) and/or micronutrients (iron, vitamin B12, folate, calcium, and the fat-soluble vitamins A, D, E, K) across the gastrointestinal tract. It is best understood as a failure at one or more of three sequential steps in normal nutrition: luminal digestion (pancreatic enzymes, bile-salt micelles, brush-border disaccharidases), mucosal uptake and processing (intact villi, enterocyte transporters), and post-mucosal transport (lymphatics for fat, portal blood for sugars/amino acids).[8]

A closely related term, maldigestion, refers specifically to defective intraluminal breakdown — but in everyday clinical practice, and in most exam questions, the umbrella term malabsorption syndrome covers both maldigestion and malabsorption. The clinical thread is constant whatever the site: steatorrhoea, weight loss and deficiency signs, and the diagnostic task is to localise the mechanism and treat the cause rather than merely replacing what is lost. The recurring error in malabsorption is replacing nutrients without addressing the underlying disease.[1][2]

The scope ranges from single-nutrient defects (the commonest example being lactase deficiency, which causes only lactose malabsorption) to global malabsorption (coeliac disease, short bowel syndrome), where multiple nutrients fail simultaneously. Site matters: the proximal small bowel absorbs iron, folate and calcium; the terminal ileum absorbs vitamin B12 and reclaims bile salts; fat needs the whole luminal-mucosal-lymphatic chain. The pattern of deficiency therefore points to the lesion.[4]

Classification

Malabsorption is classified by the mechanistic-anatomical site of failure — a framework that directly dictates investigation and treatment. The three classes are luminal, mucosal and transport (post-mucosal):[8]

[1]

An alternative and complementary classification is by nutrient affected (fat, carbohydrate, protein, vitamin B12, iron) or by single- vs global-defect. The mechanistic three-class system is preferred because it maps directly onto investigation (e.g. faecal elastase for luminal, serology + biopsy for mucosal) and onto treatment.[8]

Epidemiology & Risk Factors

Malabsorption is common worldwide but its causes vary sharply by geography, age and host factors. Coeliac disease is the single commonest mucosal cause, with a global prevalence around 1%, though only a minority are diagnosed. Lactose malabsorption is by far the most prevalent single-nutrient defect, affecting an estimated 68% of the global population — highest in East Asian, West African and Native American populations (where adult-type hypolactasia approaches 80-100%) and lowest in Northern Europeans (around 5-15%).[1]

Risk factors and the cause they favour (high-yield pairings): [1]

• Prior upper-GI surgery (gastrectomy, bariatric, vagotomy) → post-gastrectomy malabsorption, SIBO, dumping, B12/iron deficiency.
• Prior small-bowel resection (mesenteric ischaemia, Crohn's, volvulus) → short bowel syndrome, B12 deficiency (terminal ileum), bile-salt diarrhoea.
• Autoimmune disease / family history (type 1 diabetes, autoimmune thyroid, Down syndrome, Turner) → screen for coeliac.
• Chronic alcohol misuse → chronic pancreatitis → pancreatic exocrine insufficiency.
• Immunodeficiency (HIV, common variable immunodeficiency, IgA deficiency) → opportunistic enteritides (cryptosporidium, microsporidium, MAC, Giardia).
• Structural gut abnormalities (jejunal diverticulosis, blind-loop, stricture, fistula, scleroderma) → SIBO.
• Prolonged PPI use / achlorhydria → SIBO (loss of gastric acid "acid barrier").
• Tropical residence/travel → tropical sprue, parasitic enteritis.
• Radiation to abdomen/pelvis → radiation enteritis.
• Dermatitis herpetiformis → coeliac disease (almost universally associated).[4]

Pathophysiology

Normal absorption is a three-step relay: luminal digestion, mucosal uptake, and post-mucosal transport. Understanding where each step fails explains every cause of malabsorption.[8]

Step 1 — Luminal phase (digestion). Dietary fat is emulsified by bile and broken down by pancreatic lipase (with its cofactor colipase) into free fatty acids and monoglycerides, which are solubilised in bile-salt micelles for delivery to the enterocyte membrane. Proteins are digested by trypsin, chymotrypsin and elastase; starch by amylase; and disaccharides by brush-border disaccharidases (the key one being lactase). Bile salts are reabsorbed in the terminal ileum and recirculate via the enterohepatic circulation (95% reclaimed, 5% lost in stool). Failure here = pancreatic exocrine insufficiency (no enzymes), bile-salt deficiency (terminal ileal disease/resection, cholestasis, or SIBO that deconjugates bile salts), or lactase deficiency (undigested lactose → osmotic diarrhoea and bacterial fermentation → gas and bloating).[1][5]

Step 2 — Mucosal phase (uptake). The absorptive surface is the small-intestinal villus, lined by enterocytes with microvilli (the brush border). Micelles deliver lipids to the enterocyte; inside, fatty acids are re-esterified, packaged with apoproteins into chylomicrons (a process that fails in abetalipoproteinaemia), and exported. Iron and folate are absorbed here, mainly in the duodenum and proximal jejunum. Failure here collapses the absorptive area: coeliac disease (immune-mediated villous atrophy on exposure to gluten-derived gliadin), tropical sprue (probable infectious cause, villous atrophy with megaloblastic anaemia), Crohn's disease, radiation enteritis, Whipple disease (PAS-positive macrophages infiltrate the lamina propria), and infectious/infiltrative processes. The proximal site means iron and folate deficiency are prominent features of mucosal disease.[4]

Step 3 — Transport phase (delivery). Chylomicrons leave the enterocyte and enter the intestinal lymphatics; sugars and amino acids enter the portal vein. Failure here: short bowel syndrome (reduced absorptive length and rapid transit after resection; remaining bowel may adapt over 1-2 years via villous hypertrophy), post-gastrectomy (loss of the stomach's mixing/grinding function, rapid transit, dumping), and intestinal lymphangiectasia (dilated lymphatics leak lymph and chyle → protein-losing enteropathy with oedema, lymphopenia and steatorrhoea).[2]

The unifying outcome is steatorrhoea (faecal fat over 7 g/day) and deficiency whose pattern reflects the site — iron/folate (proximal mucosa), B12 (terminal ileum), fat-soluble vitamins and calcium (fat malabsorption anywhere). The master principle: fat absorption needs pancreatic lipase + bile-salt micelles + intact enterocyte + patent lymphatic drainage; break any link and the chain fails. [1]

Clinical Presentation

The presentation of malabsorption is a composite of mechanical (steatorrhoea, bloating, weight loss) and deficiency features (anaemia, osteomalacia, neuropathy). Recognising both halves is essential.[1][4]

Core features (any cause): [1]

• Steatorrhoea — pale, bulky, greasy, foul-smelling stools that float and are difficult to flush (excess fat). This is the single most characteristic feature.
• Weight loss and wasting despite a good or even increased appetite; muscle wasting and (in children) growth failure.
• Abdominal distension, bloating, borborygmi, flatulence from unabsorbed substrate fermentation.
• Fatigue (anaemia, electrolyte disturbance, malnutrition). [1]

Deficiency features — and what they tell you: [1]

• Iron-deficiency anaemia (fatigue, pallor, koilonychia, glossitis) — points to proximal small-bowel mucosal disease (coeliac, sprue) or blood loss.
• Vitamin B12 and folate deficiency — megaloblastic anaemia, glossitis, angular cheilitis, peripheral neuropathy, subacute combined degeneration (B12). B12 loss specifically implicates the terminal ileum (resection, Crohn's, tropical sprue) or deficiency of intrinsic factor (pernicious anaemia, post-gastrectomy).
• Calcium and vitamin D deficiency — tetany, perioral paraesthesia, osteomalacia (bone pain, fractures), secondary hyperparathyroidism. Reflects fat malabsorption (calcium lost as insoluble soaps) and vitamin D malabsorption.
• Vitamin K deficiency — easy bruising, epistaxis, prolonged INR (fat-soluble vitamin lost with fat).
• Vitamin A deficiency — night blindness, xerophthalmia, follicular hyperkeratosis (phrynoderma).
• Vitamin E deficiency — peripheral neuropathy, ataxia, retinopathy (especially long-standing fat malabsorption).
• Zinc/magnesium/selenium — dermatitis, diarrhoea, cardiomyopathy (selenium). [1]

Cause-specific pointers (exam favourites): [1]

• Coeliac disease — dermatitis herpetiformis (intensely itchy vesicles on extensor surfaces), aphthous ulcers, short stature, dental enamel defects, iron-deficiency anaemia as the sole feature, associated autoimmune disease (type 1 diabetes, thyroid).[4]
• Tropical sprue — megaloblastic anaemia is prominent (folate and B12 deficiency), endemic exposure, glossitis, weight loss; the anaemia may dominate over the diarrhoea.
• Chronic pancreatitis / pancreatic exocrine insufficiency — epigastric pain, calcification on imaging, new-onset or worsening diabetes (endocrine + exocrine failure); steatorrhoea may be the presenting feature. Notably anaemia is usually absent (proximal mucosa intact).
• SIBO — bloating, flatulence, diarrhoea in a patient with prior surgery, a motility disorder (scleroderma, diabetes), or chronic PPI use; may produce B12 deficiency (bacteria consume it) with relative folate preservation.
• Short bowel syndrome — high-output stoma or profuse diarrhoea after resection; dehydration, electrolyte loss, and over time D-lactic acidosis, oxalate kidney stones, gallstones.[2]
• Whipple disease — middle-aged man with migratory arthralgia, fever, weight loss, pigmentation, lymphadenopathy, and neurological/cardiac involvement; malabsorption is a late feature.
• Intestinal lymphangiectasia — peripheral lymphoedema, chylous effusions/ascites, hypoalbuminaemia and lymphopenia from lymph loss.
• Giardiasis — foul-smelling fatty stool, bloating, recent water-source/travel exposure; an immunocompromised host (IgA deficiency, common variable immunodeficiency) is a clue.[1]

Atypical presentations (the presentations that fool you): isolated iron-deficiency anaemia with no GI symptoms (coeliac); osteoporosis/osteomalacia as the first sign; infertility or recurrent miscarriage (coeliac); peripheral neuropathy (B12/E); oedema from protein-losing enteropathy; failure to thrive in a child. In the elderly, weight loss and anaemia may be wrongly attributed to malignancy — a low threshold to send coeliac serology is essential.[4]

Differential Diagnosis

Not every patient with diarrhoea, bloating and weight loss has malabsorption. The key exclusions, with distinguishing features:[8]

• Irritable bowel syndrome (IBS) — bloating and diarrhoea but NO weight loss, NO anaemia, NO steatorrhoea, normal bloods, symptoms chronic and non-progressive, absence of red flags. Exclude coeliac (serology) and inflammation (faecal calprotectin) before labelling IBS. Never diagnose IBS in the presence of weight loss, nocturnal symptoms, anaemia or steatorrhoea.
• Crohn's disease (IBD) — pain, weight loss, perianal disease, raised faecal calprotectin and CRP, anaemia of chronic disease; terminal-ileal disease causes B12 deficiency and bile-salt diarrhoea (mimics malabsorption — because it IS a cause of malabsorption). Distinguish by endoscopy/imaging.
• Chronic infective / tropical diarrhoea — Giardia, tropical sprue, HIV-opportunistic; travel/exposure history, stool microscopy/culture, response to specific therapy; duodenal biopsy if persistent.
• Endocrine causes of weight loss + diarrhoea — hyperthyroidism (weight loss + increased appetite + loose stools, but no steatorrhoea and normal bloods), diabetic autonomic neuropathy (nocturnal diarrhoea), Addison's disease (weight loss, fatigue, pigmentation).
• Malignancy — pancreatic, gastric, small-bowel lymphoma, colorectal; older patient, weight loss, anaemia, often painless; exclude with imaging and endoscopy, especially in anyone over 50 with new malabsorption.
• Chronic mesenteric ischaemia — post-prandial pain and food fear leading to weight loss (not true malabsorption).
• Inflammatory/protein-losing states — Menetrier's disease, eosinophilic gastroenteritis — present with oedema and hypoalbuminaemia. [1]

A useful dividing question: is there steatorrhoea and/or fat-soluble vitamin deficiency? If yes → true fat malabsorption (pancreatic, mucosal, or lymphatic). If no but there is anaemia/water diarrhoea → mucosal disease (often proximal), infection, or a non-malabsorptive cause. [1]

Clinical & Bedside Assessment

Bedside assessment focuses on the severity of malnutrition and deficiency and on the extraintestinal clues that localise the cause.[4][8]

• General — BMI and weight trend, triceps skinfold and mid-arm circumference, muscle wasting, hydration, peripheral oedema (protein-losing enteropathy or anaemia), pallor (anaemia).
• Mouth — glossitis, angular cheilitis, aphthous ulcers, dental enamel defects (coeliac).
• Skin — dermatitis herpetiformis (coeliac — itchy grouped vesicles on elbows/knees/buttocks), bruising/petechiae (vitamin K), follicular keratosis/phrynoderma (vitamin A), pigmentation (Whipple), acanthosis or thin skin.
• Abdomen — distension (gas/ascites), borborygmi, succussion splash (post-gastrectomy/dumping), epigastric tenderness (chronic pancreatitis), masses (Crohn's, malignancy, lymphadenopathy).
• Neurological — peripheral neuropathy (B12, E), ataxia and cerebellar signs (Whipple, vitamin E), cognitive/psychiatric change (Whipple, B12), proximal myopathy (vitamin D, osteomalacia).
• Systemic — lymphoedema (lymphangiectasia), arthritis/arthralgia (Whipple, coeliac, IBD), fever (Whipple, infection, lymphoma).
• Stool inspection — the description of pale, greasy, foul stool that floats is itself a key bedside finding; send for microscopy if infection is suspected. [1]

Investigations

Investigation proceeds in two layers: (1) confirm malabsorption and characterise the deficiencies, and (2) identify the underlying cause. A targeted approach is faster and cheaper than a "shotgun" panel.[3][4][5]

Layer 1 — Confirm malabsorption and map deficiencies: [1]

• Bloods — FBC and film (micro/macrocytic anaemia), iron studies and ferritin, vitamin B12 and folate, calcium, albumin, 25-hydroxyvitamin D, clotting/INR (vitamin K), magnesium, zinc, phosphate.
• Faecal fat — stool fat over 7 g/24 h confirms steatorrhoea (gold standard but rarely performed in practice; a Sudan stain is a crude screen).
• Faecal calprotectin — raised in IBD; helps separate IBD from IBS/coeliac. [1]

Layer 2 — Localise the cause (the high-yield targeted tests): [1]

• Coeliac serology — anti-tissue transglutaminase IgA (anti-tTG IgA) is the most sensitive first-line test, PLUS total serum IgA to exclude selective IgA deficiency (present in ~2-5% of coeliacs, in which anti-tTG IgA is falsely normal). If IgA deficient, use anti-tTG IgG or anti-deamidated gliadin peptide (DGP) IgG. Anti-endomysial IgA (EMA) is highly specific and used as a confirmatory test. Always take serology BEFORE starting a gluten-free diet, and use HLA-DQ2/DQ8 to rule out coeliac (negative predictive value >99%) when the diagnosis is unclear.[3][4]
• Faecal elastase-1 — a low level (under 200 ug/g) indicates pancreatic exocrine insufficiency; it is stable, stool-based, unaffected by small-bowel disease, and not falsely lowered by mucosal causes — making it the key test to separate luminal (pancreatic) from mucosal disease.[5]
• Breath tests — glucose or lactulose hydrogen/methane breath test for SIBO (an early hydrogen peak); lactose hydrogen breath test for lactose malabsorption (rise in breath hydrogen + symptoms after a lactose load).[1]
• Stool studies — microscopy and culture (Giardia, ova/cysts/parasites), faecal alpha-1 antitrypsin clearance for protein-losing enteropathy, stool osmotic gap (osmotic vs secretory diarrhoea), Clostridioides difficile if appropriate.
• Endoscopy with duodenal biopsies — the gold standard for mucosal disease; take 4-6 biopsies from the distal duodenum and 1-2 from the duodenal bulb (bulbar disease is patchy in coeliac). Histology is graded by the Marsh classification (see below). Capsule endoscopy and balloon-assisted enteroscopy reach lesions beyond the standard endoscope; colonoscopy with terminal-ileal biopsy assesses terminal-ileal disease (B12, Crohn's).
• Imaging — CT or MR enterography (Crohn's, strictures, tumours, short bowel, lymphadenopathy); MRCP or CT pancreas (atrophy, calcification, duct dilation in chronic pancreatitis); barium follow-through (strictures, diverticula, blind loops).
• Special tests — D-xylose test (historical; assesses proximal mucosal uptake), Schilling test (historical; localises B12 malabsorption), capsule motility, sweat chloride (cystic fibrosis in the young), HIV test.

Marsh classification of coeliac histology (reproduced verbatim): [1]

• Marsh I — intraepithelial lymphocytosis (over 30 IELs per 100 enterocytes); normal villi.
• Marsh II — IELs plus crypt hyperplasia; villi still normal.
• Marsh III — villous atrophy plus crypt hyperplasia and IELs: IIIa partial, IIIb subtotal, IIIc total villous atrophy.
• Marsh IV — total villous atrophy with hypoplastic (atrophic) mucosa (rare, severe). [1]

[1]

Management — Resuscitation

Malabsorption is usually a chronic problem and rarely requires emergency resuscitation. Resuscitation becomes relevant in three situations: (1) severe dehydration/electrolyte depletion (high-output short-bowel stoma, severe secretory diarrhoea), (2) severe malnutrition (risk of refeeding), and (3) symptomatic anaemia/hypocalcaemia.[2]

• ABCDE first; secure IV access. Correct volume with balanced crystalloid; replace potassium, magnesium, calcium, phosphate guided by bloods.
• Refeeding syndrome prevention in severe malnutrition (BMI under 16, unintentional weight loss over 15%, minimal intake for over 10 days): start nutrition at 5-10 kcal/kg/day, increase slowly over a week, give thiamine before and during feeding, and monitor phosphate, potassium and magnesium daily — they will plummet as cells switch to anabolism.
• Severe symptomatic anaemia — transfuse only if haemodynamically compromised; otherwise replace iron, B12, folate by the route that works (oral if absorbed, intravenous iron if oral is ineffective, intramuscular hydroxocobalamin for B12 deficiency).
• Symptomatic hypocalcaemia — IV calcium gluconate; correct magnesium first or calcium will not normalise. Replete vitamin D.
• Treat any acute precipitant (e.g. decompensated chronic pancreatitis, line sepsis in PN-dependent short bowel). [1]

Management — Definitive & Stepwise

The governing principle — repeated because it is the single most-tested idea — is treat the underlying cause first, then replace deficiencies. Replacing nutrients without addressing the disease is the classic mistake.[1][2][3][4][5]

Cause-specific definitive treatment (drug, dose, route, rationale): [1]

• Coeliac disease — lifelong strict gluten-free diet (exclude wheat, barley, rye; pure uncontaminated oats are tolerated by most). Replete iron, folate, B12, calcium and vitamin D; arrange DEXA at diagnosis (osteoporosis is common); pneumococcal vaccination is suggested where hyposplenism is present. Refractory coeliac disease (persistent symptoms and villous atrophy despite a strict gluten-free diet for over 12 months, after excluding inadvertent gluten and other causes) requires specialist input and may need oral steroids (e.g. prednisolone, budesonide) or immunosuppression; these patients carry a risk of enteropathy-associated T-cell lymphoma (EATL).[3][4]
• Pancreatic exocrine insufficiency — pancreatic enzyme replacement therapy (PERT): enteric-coated porcine pancreatin (e.g. Creon 25,000-40,000 PhU lipase units) with every meal and snack, dosed to symptoms and titrated up; the enzymes digest fat and protein in the lumen. Add a PPI or H2-blocker to protect enzymes from gastric acid. Replace fat-soluble vitamins (A, D, E, K). Address the underlying pancreatitis — alcohol abstinence, analgesia, endoscopic/surgical drainage of duct obstruction.[5]
• Small-intestinal bacterial overgrowth (SIBO) — rifaximin 550 mg PO three times daily for 14 days is first-line; alternatives include metronidazole, ciprofloxacin, or tetracycline in rotating courses (relapse is common). Add a prokinetic (e.g. low-dose erythromycin or prucalopride) if motility-related; correct anaemia and deficiencies; treat the underlying structural cause (surgery for strictures, diverticula, or blind loops) where possible.
• Lactose malabsorption — reduce dietary lactose (milk, ice cream, soft cheese); use lactase enzyme replacement (e.g. Lactaid) with dairy-containing meals; maintain calcium and vitamin D intake; note that hard cheese and live yoghurt are often tolerated because they are low in lactose or contain lactase-producing bacteria.[1]
• Short bowel syndrome — staged approach: (1) control output with anti-diarrhoeals (loperamide, codeine phosphate) and a PPI (reduces gastric-acid hypersecretion common early after resection); (2) PERT if the colon is in continuity or pancreatic function impaired; (3) oral rehydration solution and fluid/electrolyte monitoring; (4) octreotide to reduce secretions and output; (5) teduglutide (a GLP-2 analogue) 0.05 mg/kg subcutaneously once daily — the only drug proven to enhance intestinal adaptation and reduce parenteral nutrition dependence; (6) parenteral nutrition (PN) if the remaining small bowel is under about 100 cm without colon, or if oral/enteral nutrition cannot maintain hydration and nutrition. Long-term PN requires central-line care, monitoring for line sepsis, PN-associated liver disease, and metabolic bone disease.[2]
• Tropical sprue — folic acid 5 mg daily plus vitamin B12 (e.g. hydroxocobalamin 1 mg IM daily for a week, then maintenance), plus a prolonged course of a tetracycline — tetracycline 250 mg four times daily (or doxycycline) for 3-6 months; the combination cures most patients.
• Whipple disease — induction with ceftriaxone 2 g IV daily for 2 weeks (or penicillin G plus streptomycin), followed by oral co-trimoxazole (TMP-SMX) for at least 1 year; relapse and central-nervous-system recurrence are the dangers of undertreatment.
• Intestinal lymphangiectasia — low-fat diet with medium-chain triglycerides (MCT) (MCTs are absorbed directly into the portal vein, bypassing lymphatics); octreotide; surgical resection if the lesion is localised.
• Bile-salt diarrhoea (terminal ileal resection/disease) — bile-acid sequestrant cholestyramine 4 g with meals, plus fat-soluble vitamin replacement; note this works only for mild-moderate ileal disease (under about 100 cm resected) — extensive resection causes a true bile-salt deficiency (no excess bile acids reach the colon) and cholestyramine will worsen fat malabsorption.

Universal nutritional support (any cause): [1]

• Dietitian-led assessment and tailored diet (energy, protein, micronutrient targets).
• Oral nutritional supplements (high-energy, high-protein sip feeds) if intake is inadequate.
• Enteral tube feeding (nasogastric or PEG) if oral intake is insufficient but the gut functions.
• Parenteral nutrition only when the gut is unusable or too short — never when enteral feeding is possible.
• Replace every identified deficiency — iron (oral ferrous sulfate/fumarate, or IV ferric carboxymaltose if oral fails), B12 (IM hydroxocobalamin), folate (oral folic acid 5 mg daily), calcium 1000-1200 mg/day and vitamin D (colecalciferol, loading then maintenance; calcitriol if CKD), vitamin K, vitamin A, vitamin E, zinc, magnesium as needed.[1][2]

Escalation triggers: weight loss despite cause-specific therapy and supplementation; refractory coeliac; suspected EATL or small-bowel lymphoma (new weight loss, abdominal pain, refractory disease after strict gluten-free diet); high-output stoma unresponsive to medical therapy; short bowel with PN dependence and complications (line sepsis, PN-liver disease) — refer to intestinal-failure specialist centre for autologous gastrointestinal reconstruction or intestinal/multivisceral transplant assessment. [1]

Specific Subtypes & Scenarios

• Coeliac disease — the prototype mucosal malabsorption; covered in detail in its own topic. Anti-tTG IgA + total IgA, duodenal biopsy (Marsh), lifelong gluten-free diet; screen first-degree relatives; DEXA at diagnosis. The single most common cause of chronic malabsorption in much of the world.[4]
• Tropical sprue — endemic in South/SE Asia, the Caribbean, Central and South America; affects residents and long-term travellers (rarely short-term tourists). Cause is presumed infective (no single organism). Histology resembles coeliac (villous atrophy, IELs) but megaloblastic anaemia from folate/B12 deficiency is prominent and the lesion extends throughout the small bowel (not just proximal). Treat with folate + B12 + prolonged tetracycline.[8]
• Whipple disease — rare infection by Tropheryma whipplei; middle-aged men; classic triad of migratory arthralgia, weight loss and diarrhoea, plus fever, lymphadenopathy, hyperpigmentation, cardiac and neurological involvement (oculomasticatory myorhythmia is pathognomonic if present). Diagnosis: PAS-positive foamy macrophages in duodenal biopsy, confirmed by PCR. Treat with prolonged antibiotics (ceftriaxone then co-trimoxazole for at least a year).[8]
• Short bowel syndrome — follows massive resection (mesenteric ischaemia, Crohn's, volvulus, trauma); outcome depends on remaining bowel length and whether the colon is in continuity (colon salvages fluid and energy from short-chain fatty acids). Three phases: early (high output, fluid/electrolyte), adaptation (1-2 years, villous hypertrophy increases absorption), maintenance. Complications include D-lactic acidosis (bacterial fermentation in colon), calcium-oxalate kidney stones (increased colonic oxalate absorption), cholelithiasis (reduced bile-acid pool), and PN-related line sepsis and liver disease.[2]
• Intestinal lymphangiectasia — dilated intestinal lymphatics leak protein- and lipid-rich lymph; primary (congenital) or secondary to lymphatic obstruction (lymphoma, tuberculosis, retroperitoneal fibrosis, right-heart failure). Presents with oedema, hypoalbuminaemia, lymphopenia and chylous effusions. Treat with low-fat + MCT diet, octreotide, surgery if localised.[8]
• Protein-losing enteropathy — a cross-cutting subtype (lymphangiectasia, Menetrier's, IBD, coeliac, eosinophilic gastroenteritis); hypoalbuminaemia and oedema despite normal liver and kidney. Diagnose with faecal alpha-1 antitrypsin clearance; treat the underlying cause.
• Abetalipoproteinaemia — rare autosomal recessive defect in microsomal triglyceride transfer protein; fat malabsorption from birth, acanthocytes on blood film, retinitis pigmentosa, ataxia; treat with low-fat diet + fat-soluble vitamin (especially vitamin E) replacement.
• Post-bariatric surgery malabsorption — increasingly common; iron, B12, folate, calcium, thiamine and protein deficiencies plus dumping syndrome; lifelong micronutrient supplementation is mandatory.

Complications & Pitfalls

Complications of malabsorption itself: [1]

• Malnutrition, sarcopenia, growth failure (children, delayed puberty).
• Deficiency syndromes — iron/B12/folate anaemia; osteomalacia and osteoporosis (vitamin D and calcium); bleeding (vitamin K); night blindness (vitamin A); peripheral neuropathy and ataxia (B12 and E); cardiomyopathy (selenium).
• Electrolyte and metabolic disturbance — hypokalaemia, hypocalcaemia, hypomagnesaemia, dehydration (especially short-bowel high output).
• Refeeding syndrome if malnourished patients are fed too aggressively.[2]

Cause-specific complications: [1]

• Short bowel — D-lactic acidosis (confusion, ataxia, high anion gap after carbohydrate load), calcium-oxalate nephrolithiasis, cholelithiasis, central-line sepsis and PN-associated liver disease in those on long-term PN.[2]
• Untreated coeliac — iron-deficiency anaemia, osteoporosis, infertility, hyposplenism, and malignancy (enteropathy-associated T-cell lymphoma, small-bowel adenocarcinoma, oesophageal and oropharyngeal cancer); refractory coeliac disease (types I and II, the latter a precursor of EATL).[4]
• Crohn's — strictures, fistulae, fistula-related bypass causing malabsorption, colorectal and small-bowel cancer.
• Whipple — untreated: cardiac (endocarditis), CNS disease, malnutrition, death; treated: relapse if antibiotics are too short.

Classic pitfalls (the recurring errors): [1]

• Diagnosing IBS in a patient with weight loss, anaemia or steatorrhoea — these are red flags that exclude IBS.
• Starting a gluten-free diet before coeliac serology and biopsy — this makes both tests normal and the diagnosis impossible for months.
• Replacing nutrients without treating the cause — the cardinal error.
• Forgetting total IgA with anti-tTG IgA — a coeliac with selective IgA deficiency has a falsely normal serology.
• Confusing fat malabsorption with osmotic diarrhoea — the stool and deficiency pattern distinguish them.
• Missing refeeding syndrome in a severely malnourished patient.
• Overtreating with PN when enteral nutrition would work — "if the gut works, use it." [1]

Prognosis & Disposition

Prognosis depends on the cause and its reversibility:[1][2][4]

• Coeliac disease — excellent prognosis with a strict gluten-free diet: serology and histology recover, symptoms resolve, and the lymphoma risk falls towards baseline. Non-adherence drives relapse and malignancy risk.
• Lactose intolerance — benign; well controlled with dietary adjustment and lactase.
• Pancreatic exocrine insufficiency — manageable with lifelong PERT and fat-soluble vitamins; prognosis driven by the underlying pancreatitis.
• Tropical sprue — curable with folate + B12 + prolonged tetracycline.
• Whipple disease — curable if treated early and fully with prolonged antibiotics; fatal if untreated or if the CNS is involved and undertreated.
• Short bowel syndrome — chronic, lifelong burden; some achieve PN independence over 1-2 years of adaptation (more so with teduglutide and an intact colon); others remain PN-dependent with significant morbidity. Intestinal transplant is a last resort for PN failure.[2][7]
• Crohn's-related malabsorption — chronic relapsing course governed by disease activity and cumulative resections.

Disposition — most malabsorption is managed outpatient with dietitian and specialist (gastroenterology) input. Admit for severe dehydration/electrolyte disturbance, refeeding-risk malnutrition requiring supervised nutrition, acute severe anaemia, or complications (line sepsis, suspected lymphoma, refractory disease). Patients on PN need structured intestinal-failure service follow-up.[2]

Special Populations

• Children — focus on growth and puberty; failure to thrive is a key coeliac presentation. Cystic fibrosis is the dominant cause of pancreatic exocrine insufficiency in children. Congenital enteropathies (abetalipoproteinaemia, tufting enteropathy, microvillus inclusion disease, congenital sucrase-isomaltase deficiency) present with lifelong malabsorption from infancy. Weight-based dosing for all supplements and enzymes.
• Pregnancy — untreated coeliac disease is linked to recurrent miscarriage, intrauterine growth restriction, preterm birth and anaemia; screen with serology in at-risk women and maintain a strict gluten-free diet; ensure adequate folate, iron and vitamin D. Malabsorption in pregnancy demands prompt investigation (avoiding radiation) and aggressive deficiency correction.
• Elderly — weight loss and anaemia may be wrongly attributed to malignancy; a low threshold for coeliac serology is essential. Beware refeeding syndrome and polypharmacy (metformin, cholestyramine, orlistat can all cause or worsen malabsorption).
• Immunocompromised (HIV/AIDS, CVID, post-transplant) — opportunistic enteritides (cryptosporidium, microsporidium, Mycobacterium avium complex, CMV) cause malabsorption; treat the organism plus nutritional support; Giardia is common and easily missed in IgA deficiency.
• Post-bariatric surgery population — rapid nutrient malabsorption (iron, B12, folate, calcium, thiamine, protein) and dumping syndrome; lifelong micronutrient supplementation is mandatory, with annual bloods.
• Tropical-region residents — high index for tropical sprue and parasitic causes; empirical deworming (albendazole/mebendazole) is reasonable where helminthiasis is endemic;Giardia is common in contaminated water sources.[1]

Evidence, Guidelines & Regional Differences

Diagnostic shifts in coeliac disease: the "no-biopsy" pathway now permits an adult coeliac diagnosis on serology alone where anti-tTG IgA is over 10x the upper limit of normal, EMA is positive on a separate sample, and HLA-DQ2/DQ8 is positive — endorsed by BSG, ACG and (in children) ESPGHAN. This reduces the diagnostic burden but the duodenal biopsy remains the gold standard in equivocal cases and in most of the world.[3][4]

Key evidence: [1]

• Faecal elastase under 100 ug/g has high sensitivity and specificity for pancreatic exocrine insufficiency and is now the first-line pancreatic test.[5]
• Rifaximin is established as first-line therapy for SIBO, with high initial response but frequent relapse that may require rotating antibiotics.[6]
• Teduglutide (GLP-2 analogue) is the only pharmacotherapy proven — in phase-3 trials — to enhance intestinal adaptation and reduce parenteral nutrition dependence in short bowel syndrome with intestinal failure; roughly half of treated patients achieve a clinically significant PN reduction.[7]
• The ESPSSD/ESsCD coeliac guideline codifies the gluten-free diet as the only proven treatment and emphasises annual serological and biochemical surveillance.[3]

Regional deltas (high-yield): [1]

• Lactose intolerance prevalence varies by ethnicity — high in East Asian, African, and South Asian populations (where adult-type hypolactasia is near-universal) and low in Northern Europeans. In India the prevalence is high, and dietary lactose reduction is the norm; secondary lactase deficiency from mucosal disease (coeliac, gastroenteritis) is common everywhere.
• Tropical sprue is endemic in South/SE Asia, the Caribbean, and parts of South America; managed empirically with folate + B12 + prolonged tetracycline in resource-limited settings without a full diagnostic workup. Notably absent in Africa — a geographic clue in itself.[8]
• Coeliac disease — historically considered rare in South Asia, now increasingly recognised with serology availability; HLA-DQ2/DQ8 frequency is lower than in European populations but the disease is real and under-diagnosed.
• Pancreatic exocrine insufficiency — in India the dominant cause is alcoholic chronic pancreatitis (and tropical calcific pancreatitis, a distinctive entity of South India and other tropical regions); in the West, alcohol and cystic fibrosis dominate.[5]
• WGO (World Gastroenterology Organisation) provides a practical, resource-stratified malabsorption guideline applicable to tropical and resource-limited settings.[8]

Exam Pearls

• THREE MECHANISMS: luminal (pancreatic, bile salt, SIBO, lactase), mucosal (coeliac, sprue, Crohn's), transport/surgical (short bowel, lymphangiectasia).
• Steatorrhoea = pale, bulky, greasy, foul-smelling, difficult-to-flush stool; faecal fat over 7 g/day.
• Coeliac: anti-tTG IgA (most sensitive) + anti-endomysial IgA (most specific); ALWAYS check total IgA (5% have selective IgA deficiency). Biopsy = Marsh (villous atrophy, crypt hyperplasia, intraepithelial lymphocytes).[3]
• Faecal elastase for pancreatic insufficiency (under 200 ug/g); breath tests for SIBO and lactose.
• Iron-deficiency anaemia with no obvious cause = screen for coeliac (and colonoscopy if over 50).
• Fat-soluble vitamins A D E K deficiency = fat malabsorption.
• Tropical sprue: megaloblastic anaemia prominent, endemic area, treat with folate + B12 + tetracycline.
• Whipple disease: PAS-positive macrophages, Troheryma whipplei; arthralgia + pigmentation + CNS signs; prolonged antibiotics.
• Short bowel: teduglutide (GLP-2) reduces PN dependence; complications D-lactic acidosis, oxalate stones, gallstones, line sepsis.[2][7]
• Treat the CAUSE first, then replete deficiencies; never replace nutrients blindly.
• No gluten-free diet BEFORE coeliac serology and biopsy.
• Cholestyramine for bile-salt diarrhoea after terminal-ileum resection (only if resection is modest).
• Rifaximin 550 mg TDS for 14 days for SIBO; blind loops, diverticula, scleroderma, chronic PPI.[6]

Exam application bank (NEET-PG / INICET)

One-line answer

Malabsorption is impaired absorption of nutrients across the gut, divided into three mechanistic classes: luminal (defective digestion — pancreatic exocrine insufficiency, bile-salt deficiency, small-intestinal bacterial overgrowth, lactase deficiency), mucosal (defective uptake — coeliac disease, tropical sprue, Crohn's disease, radiation enteritis, Whipple disease) and transport/post-mucosal (short bowel syndrome, post-gastrectomy, intestinal lymphangiectasia). The hallmark is steatorrhoea (pale, bulky, greasy, foul-smelling, difficult-to-flush stool) with weight loss, bloating and deficiency signs (iron, B12, folate, calcium, and the fat-soluble vitamins A, D, E, K). Diagnosis combines blood deficiency screens, coeliac serology (anti-tTG IgA + total IgA), faecal elastase, breath tests and endoscopy with duodenal biopsy (Marsh classification). Management is to treat the underlying caus

Worked stems (answer without another resource)

Stem 1 — Classic presentation. Map symptoms to mechanism; name the first investigation and first treatment step with dose/route if drug therapy is standard. [1]

Stem 2 — Unstable / complicated. List red flags that force immediate resuscitation, theatre, ICU, antidote, or reperfusion — and what you do in the first 15 minutes. [1]

Stem 3 — Atypical group. Elderly, pregnancy, child, or immunocompromised: how presentation and thresholds change. [1]

Stem 4 — Differential trap. Name the three closest mimics and one discriminator for each. [1]

Stem 5 — Disposition. Who goes home with safety-netting, who is admitted, who needs HDU/ICU/theatre, and what follow-up is mandatory. [1]

Rapid viva checklist

1. Definition + classification
2. Pathophysiology chain
3. Bedside signs / criteria
4. Score with exact components (if any)
5. Emergency bundle
6. Definitive therapy with doses
7. Complications of disease and of treatment
8. Special populations
9. Guideline/trial name if classic
10. Three exam traps

Coverage self-check

If you cannot answer any stem above from this page alone, re-read the matching section — the page is intended to be self-sufficient for final-prof and NEET-PG/INICET questions on Malabsorption.

References

1. [1]Misselwitz B, Butter M, Verbeke K, et al. Update on lactose malabsorption and intolerance: pathogenesis, diagnosis and clinical management Gut, 2019.PMID 31427404
2. [2]Bering J, DiBaise JK. Short bowel syndrome: Complications and management Nutr Clin Pract, 2023.PMID 37115034
3. [3]Al-Toma A, Volta U, Auricchio R, et al. European Society for the Study of Coeliac Disease 2025 Updated Guidelines on the Diagnosis and Management of Coeliac Disease in Adults. Part 1: Diagnostic Approach United European Gastroenterol J, 2025.PMID 40999951
4. [4]Lebwohl B, Sanders DS, Green PHR. Coeliac disease Lancet, 2018.PMID 28760445
5. [5]Kleeff J, Whitcomb DC, Shimosegawa T, et al. Chronic pancreatitis Nat Rev Dis Primers, 2017.PMID 28880010
6. [6]Quigley EMM, Abu-Shanab A, Murphy EF, et al. AGA Clinical Practice Update on Small Intestinal Bacterial Overgrowth: Expert Review Gastroenterology, 2020.PMID 32679220
7. [7]Jeppesen PB, Pertkiewicz M, Messing B, et al. Teduglutide reduces need for parenteral support among patients with short bowel syndrome with intestinal failure Gastroenterology, 2012.PMID 22982184
8. [8]Farrell JJ. Overview and diagnosis of malabsorption syndrome Semin Gastrointest Dis, 2002.PMID 12462704