Neonatal hypoglycaemia — formative SAQs

SAQ 1 (10)

A two-hour-old 39-week infant of a gestational diabetic mother is jittery. A bedside pre-feed glucose is 1.6 mmol/L after a breastfeed. The infant is plump and plethoric with disproportionate truncal adiposity. [4] [2]

1. Define neonatal hypoglycaemia and state the commonly used operational thresholds by postnatal age. (3) [3]
2. Explain the mechanism by which this infant became hypoglycaemic. (3) [4]
3. Describe your stepwise management of his hypoglycaemia. (4) [2] [1]

Model answer

1. Neonatal hypoglycaemia is best defined as a blood glucose below the operational threshold at which intervention is warranted, rather than a single fixed number. Commonly used thresholds rise with age: below 2.0 mmol/L in the first 24 hours, below 2.6 mmol/L from 24 to 48 hours, and below 3.0 mmol/L beyond 48 hours; the symptomatic infant is treated at any low value. Local policy (AAP, PES, NICE, ADIPS) varies. [3]
2. Maternal glucose crossed the placenta freely but maternal insulin did not, so chronic intrauterine hyperglycaemia drove fetal pancreatic hyperinsulinaemia. At cord clamping the maternal glucose supply stops abruptly, but insulin persists — driving glucose into cells and suppressing ketogenesis, so the blood glucose falls steeply in the first hours and the brain loses both glucose and ketone fuel. [4]
3. Feed early and frequently (breast milk first, at least 2–3 hourly), check pre-feed glucose on a schedule, and treat low glucose up the ladder: first feed, then buccal 40% dextrose gel 200 mg/kg with a feed and recheck in 30 minutes, then intravenous 10% dextrose 2 mL/kg bolus and an escalating infusion titrated to a glucose infusion rate of 6–8 mg/kg/min, with glucagon or hydrocortisone reserved for refractory cases. Treat the infant and the trend, not the number alone. [2] [1]

SAQ 2 (10)

A 4-day-old term infant has recurrent hypoglycaemia requiring a glucose infusion rate of 14 mg/kg/min. A critical sample at glucose 1.4 mmol/L shows insulin 30 mU/L with low free fatty acids and low beta-hydroxybutyrate, and a brisk glucose rise after glucagon. [5] [6]

1. What is the most likely diagnosis, and what features of the critical sample support it? (4) [5]
2. List four pathological causes of persistent neonatal hypoglycaemia to exclude when hypoglycaemia lasts beyond 48–72 hours. (2) [5]
3. Outline your initial management and the investigations and referrals you would arrange. (4) [6]

Model answer

1. Hyperinsulinaemic hypoglycaemia (congenital hyperinsulinism). The critical sample shows an inappropriately non-suppressed insulin at the time of hypoglycaemia, with suppressed free fatty acids and ketones (insulin suppresses them), and a brisk glucose rise after glucagon (a glycogen-rich liver with insulin blocking release). The high glucose requirement (>10–12 mg/kg/min) and persistence beyond 72 hours support the diagnosis. [5]
2. Congenital hyperinsulinism; inborn errors of metabolism (fatty-acid oxidation defects, galactosaemia, glycogen storage disease, organic acidaemias); endocrine deficiency (hypopituitarism, adrenal insufficiency, hypothyroidism); and sepsis. [5]
3. Stabilise with an escalating intravenous dextrose infusion titrated to maintain normoglycaemia, and add glucagon or hydrocortisone if refractory. Take the critical sample and a metabolic and endocrine workup (free fatty acids, beta-hydroxybutyrate, lactate, ammonia, cortisol, growth hormone, plasma amino acids, acylcarnitines, urine organic acids). Refer urgently to paediatric endocrinology and genetics for a diazoxide trial and possible 18-FDOPA imaging and surgery, because early diagnosis and treatment change the neurological outcome. [6]