Diffuse Alveolar Haemorrhage — Written Clinical Reasoning

Model answer — Part A: the haemoptysis-absent pulmonary-renal presentation

Frame the problem. Falling haemoglobin, new diffuse ground-glass infiltrates and worsening hypoxaemia are diffuse alveolar haemorrhage until proven otherwise — and the absence of haemoptysis does not argue against it, because up to a third of DAH presents without it. The active urine sediment makes this a pulmonary-renal syndrome, which shortens the differential to the immune causes: ANCA-associated vasculitis, anti-GBM disease and SLE [1] [2].

Confirm the bleeding. The diagnostic move is bronchoscopy with serial bronchoalveolar lavage: three sequential aliquots from the same segment becoming progressively bloodier confirms DAH, and haemosiderin-laden macrophages on Prussian blue staining confirm bleeding of at least 48–72 hours' duration. Lavage also samples for infection, the main mimic [1].

Hunt the cause in parallel, same day. ANCA by ELISA with MPO and PR3 specificity, anti-GBM antibody, ANA with dsDNA, complement C3/C4, and antiphospholipid antibodies if the story suggests; urine microscopy for dysmorphic red cells and red-cell casts with protein:creatinine ratio; creatinine trend; and an echocardiogram to exclude mitral stenosis before any idiopathic label. In a 28-year-old woman, SLE and MPO-ANCA disease (MPA) lead the pre-test probabilities [1] [7].

Renal biopsy once stable: pauci-immune necrotising crescentic GN (ANCA), linear IgG (anti-GBM) or full-house immune-complex GN (lupus) — the pattern determines both treatment and prognosis. Tissue must never delay emergency treatment in a deteriorating patient [7].

Close the loop: the differential also includes bland causes (coagulopathy, toxins) and idiopathic pulmonary haemosiderosis — but IPH is a diagnosis of exclusion and is untenable here because the urine is active [2].

Model answer — Part B: anti-GBM disease in the young smoker

Immediate management runs on two rails. Supportively: ICU, airway and breathing support with lung-protective ventilation if required, transfusion as needed, and correction of any coagulopathy. Definitively: start treatment on the serology without waiting for the biopsy — daily plasma exchange (typically 10–14 days or until the antibody clears) plus pulse methylprednisolone 500–1000 mg IV daily for 3 days and cyclophosphamide to suppress new antibody synthesis [3] [4].

Why plasma exchange is the cornerstone: it physically removes the pathogenic anti-GBM IgG. This is the one pulmonary-renal indication where apheresis is uncontested — contrast ANCA vasculitis, where PEXIVAS showed no overall death-or-ESKD benefit and plasma exchange is no longer routine [3] [6].

Counselling on prognosis follows the Johnson series logic: renal recovery correlates with creatinine at presentation — patients treated before dialysis dependence often recover renal function, while those dialysis-dependent with crescents in essentially all glomeruli rarely do. His creatinine of 520 micromol/L is ominous for the kidney, but the lung is treated regardless: pulmonary haemorrhage is itself the indication for full therapy even when renal salvage is unlikely [4].

Relapse risk and the smoking conversation: monotypic anti-GBM disease rarely relapses once the antibody is cleared, so prolonged maintenance immunosuppression is usually unnecessary — unless he is double-positive with ANCA (check), which converts him to the ANCA relapse pattern. Smoking cessation is therapeutic, not cosmetic: cigarette exposure unmasks the cryptic alveolar epitope that triggers lung haemorrhage, and continued smoking risks recurrent pulmonary bleeding [5] [3].

Finish the system: hepatitis and HIV screening before immunosuppression, PJP prophylaxis on combination therapy, fertility counselling before cyclophosphamide, vaccination planning, and documented smoking-cessation support — the marks are in the completeness, not just the apheresis [7].