Hypoglycaemia Workup in Children
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Direct answer
Hypoglycaemia in a child is a number plus a context: a plasma glucose below 70 mg/dL that triggers evaluation, with values below 54 mg/dL clinically significant and any symptomatic level an emergency. The diagnostic strategy rests on Whipple's triad — symptoms consistent with hypoglycaemia, a laboratory-verified low glucose at the time, and relief after glucose — because a single low fingerstick value in a well child means nothing. The core discipline is the critical sample drawn at the moment of hypoglycaemia: glucose, insulin, C-peptide, beta-hydroxybutyrate, free fatty acids, lactate, ammonia, growth hormone, cortisol and acylcarnitines, which together separate the three great families — hyperinsulinaemic (insulin measurable with suppressed ketones), ketotic (counter-regulatory hormone deficiency, ketotic hypoglycaemia, inborn errors) and hypoketotic defects of fat metabolism. Treatment follows the cause, from a dextrose bolus and infusion to diazoxide for congenital hyperinsulinism.
What you must remember
- Thresholds to quote: below 70 mg/dL warrants evaluation in any child at risk; below 54 mg/dL is clinically significant by international consensus; in the neonate, values below 45 mg/dL in the first 24 hours and below 50 to 60 thereafter demand action — with symptomatic neonates treated instantly regardless of the exact number.
- Whipple's triad: symptoms (autonomic — sweating, trembling, pallor; neuroglycopenic — confusion, seizures, drowsiness), a confirmed laboratory low value during symptoms, and resolution with glucose — all three before committing to a diagnosis.
- Hyperinsulinaemic hypoglycaemia signature: detectable insulin (commonly ≥3 mIU/L) with C-peptide inappropriately present, suppressed beta-hydroxybutyrate and free fatty acids, and a glucose rise above 30 mg/dL after glucagon — the glucagon response is the bedside proof. A sample not drawn at the moment of hypoglycaemia is a lost diagnostic opportunity.
- Hyperinsulinism causes: perinatal stress and maternal diabetes (commonest, transient), congenital hyperinsulinism from ABCC8 or KCNJ11 mutations (severe, diazoxide-unresponsive, focal lesions curable by surgery), and Beckwith-Wiedemann syndrome with macroglossia and omphalocele.
- Ketotic causes: ketotic hypoglycaemia of toddlerhood (commonest in children 1 to 5 years, thin build, long fast or illness, outgrown with age), growth hormone or cortisol deficiency, and fructose or aminoacid metabolism errors; fatty acid oxidation defects, by contrast, cause hypoketotic hypoglycaemia with dicarboxylic aciduria — never fast these children.
- Treatment arithmetic: 2 mL/kg of 10 per cent dextrose as a bolus, then 6 to 8 mg/kg/min infusion; for hyperinsulinism add diazoxide 5 to 15 mg/kg/day (first line) with chlorothiazide, then octreotide for diazoxide failures; uncooked cornstarch at bedtime prevents recurrent ketotic episodes. In Indian district hospitals without bedside ketone meters, saving a spun serum sample at the time of hypoglycaemia lets insulin, cortisol and beta-hydroxybutyrate be sent later.
Reading one hypoglycaemic child correctly
A nine-month-old, admitted at 6 a.m. after a vomiting illness with skipped dinner, has glucose 34 mg/dL and is drowsy. The team draws the critical sample before treating: insulin undetectable, beta-hydroxybutyrate high (4.5 mmol/L), free fatty acids raised, cortisol and growth hormone appropriately elevated, acylcarnitines normal. This is the physiology of correct fasting — ketotic hypoglycaemia, the most common form in childhood. Treatment is glucose now, then prevention: regular meals, a bedtime snack, cornstarch during illness and a written sick-day plan; most children outgrow it by 5 to 6 years.
Now the counter-case: a two-month-old, large at birth with macroglossia and an umbilical hernia, has repeated fasting hypoglycaemia with insulin 12 mIU/L, beta-hydroxybutyrate suppressed, and a 60 mg/dL jump after glucagon. Congenital hyperinsulinism is at the table; diazoxide is started, and failure to respond points to a KATP-channel mutation — imaging to separate a focal lesion (curable by limited surgery) from diffuse disease. The two infants shared a number; the critical sample divided their worlds.
Where students slip
The commonest error is treating the number and losing the diagnosis — giving dextrose before any sample is drawn converts a once-in-a-lifetime diagnostic window into a permanent question mark; the answer is to draw whatever is possible in 60 seconds, or at minimum save serum. The second error is calling every fasting low value "hypoglycaemia disorder" — Whipple's triad exists precisely to filter this. The third is the ketone logic reversed: assuming ketones mean something sinister, when in fact the dangerous hypoglycaemias are the hypoketotic ones (hyperinsulinism, fatty acid oxidation defects), because ketones are the brain's alternative fuel and their absence starves it twice over. Finally, in the neonate who fits, remember that hypoglycaemia plus micropenis or midline defects means pituitary deficiency until excluded.
Frequently asked questions
What constitutes Whipple's triad in a child?
Symptoms consistent with low glucose, a laboratory-confirmed low value at that moment, and prompt relief after glucose administration.
Which samples are collected during a hypoglycaemic episode?
Glucose, insulin, C-peptide, beta-hydroxybutyrate, free fatty acids, lactate, ammonia, growth hormone, cortisol and acylcarnitines — the critical sample that defines the cause.
What laboratory signature indicates hyperinsulinaemic hypoglycaemia?
Measurable insulin and C-peptide with suppressed ketones and free fatty acids, and an exaggerated glucose rise (over 30 mg/dL) after glucagon.
What is the first-line drug for congenital hyperinsulinism?
Diazoxide, 5 to 15 mg/kg/day in three divided doses, with chlorothiazide; diazoxide failure suggests a KATP-channel mutation requiring further therapy and possible surgery.
Why are fatty acid oxidation defects dangerous during fasting?
Impaired beta-oxidation blocks ketone production, so fasting deprives the brain of both glucose and ketones, producing hypoketotic hypoglycaemia with risk of Reye-like illness or sudden death.