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29. Clinical biochemistry of hypoglycaemia and hyperglycaemia

Hypoglycaemia

Hypoglycaemia is defined as a serum glucose level below 3.5 mmol/L. It most frequently occurs in diabetics in association with taking too much insulin or other antidiabetic (glucose-lowering) drugs. It may also occur in chronic alcoholics. Rare causes include beta blockers and insulinomas. It’s most characteristic for type 1 diabetics.

Types of hypoglycaemia

Postprandial (or reactive) hypoglycaemia refers to any hypoglycaemia that occurs after food intake. It may occur due to:

Late dumping syndrome involves a rapid emptying of carbohydrates into the intestine, which triggers a massive insulin response. This insulin response may cause postprandial hypoglycaemia.

Fasting hypoglycaemia is any hypoglycaemia that occurs unrelated to food intake. It may occur due to:

  • Increased glucose usage
  • Decreased glucose production
    • End-stage of starvation
    • Premature babies – they don’t have sufficient glycogen stores
    • Acute liver failure
    • Adrenal, pituitary, glucagon insufficiency
    • Alcohol intoxication

Symptoms

The symptoms of hypoglycaemia can be divided into two groups: those that occur due to increased adrenergic activity and those that occur due to decreased glucose supply to the brain:

  • Adrenergic symptoms – appear around 3.0 mmol/L
    • Sweating
    • Tachycardia
    • Palpitation
    • Aggressiveness
    • Hunger
  • Neuroglycopaenic symptoms – appear around 2.8 mmol/L
    • Headache
    • Weakness
    • Dizziness
    • Confusion
    • Convulsions
    • Coma

Death may occur in severe cases.

Beta-blockers may mask the adrenergic symptoms of hypoglycaemia.

Hyperglycaemia

Hyperglycaemia refers to higher-than-normal blood glucose level. The upper limit of "normal" glucose level depends on whether there is fasting or not. When fasting, the upper normal level is 7.0 mM.

Chronic hyperglycaemia is a defining feature of diabetes mellitus.