A blood glucose measurement is part of the initial investigation of any patient presenting with disorientation or coma. Diagnosis is made by the measurement of blood glucose using arterialized capillary blood from a fingerprick. Whole-blood glucose measured in this way will be 10 to 15 per cent lower than corresponding plasma samples. If hypoglycemia is found, blood should be drawn for plasma glucose in a fluoride or oxalate tube, together with plasma insulin, C peptide, and cortisol. To assist future diagnosis, samples should be taken before treatment is initiated. A low ratio of C peptide to insulin suggests exogenous insulin administration, whereas a normal ratio suggests an endogenous source of insulin.
Given the wide range of 'normal' blood glucose values, diagnosis of pathological hypoglycemia depends on the clinical recovery from neuroglycopenic symptoms after an intravenous infusion of glucose.
Patients with hypoglycemia will usually present to critical care in one of the following groups.
1. Brittle diabetics who have missed a meal or taken an inappropriate dose of insulin; often these younger patients will have been found in coma, and may have already been treated in situ with intramuscular glucagon or a glucose infusion.
2. An older group or their relatives with access to oral hypoglycemic drugs who present in coma having intentionally or otherwise taken an overdose, sometimes in combination with additional prescribed agents and alcohol.
3. Alcohol-induced hypoglycemia; most, but not all, of these patients are chronic alcoholics. Hypoglycemia is an incidental but dangerous finding as these patients are often assumed to be in coma of alcoholic etiology. A significant proportion of custodial deaths are attributed to this misunderstanding. Paradoxically, the most severe cirrhotics rarely develop alcohol-induced hypoglycemia as their liver function is so poor that they cannot generate sufficient NADH to inhibit gluconeogenesis.
4. The hospital in-patient with an insulin-secreting tumor who is being prepared for surgery. Rarely, hypoglycemia is part of the initial presentation of this disease.
5. As part of the initial presentation of Addison's disease, where hypoglycemia is an additional finding in a patient with glucocorticoid deficiency.
6. As part of the symptomatology of a severe illness, such as fulminant liver disease, acute and chronic pancreatitis, malaria, or sepsis.
7. As an endstage in the symptoms of starvation, particularly in the edematous variety of kwashiorkor. Paradoxically, starvation is rarely associated with hypoglycemia in its early stages, despite exhaustion of glycogen stores, as ketone bodies can act as energy substrates for the brain. Hypoglycemia is occasionally seen and is a poor prognostic sign in anorexia nervosa.
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