Investigation of hypoglycaemia in infancy
It is most important to ensure that appropriate samples are collected at the time of the hypoglycaemia. Certain tests should be performed as soon as practically possible, including:
- fluoride oxalate blood: free fatty acids, 3 hydroxybutyrate, lactate
- urine: organic acids
Other tests should then follow as indicated either by the clinical presentation or the results of the earlier tests.
- The baby’s age, gestational age and birthweight are important considerations. Transient hypoglycaemia is common in low birthweight babies in the first 2 or 3 days of life. This is largely due to inadequate glycogen stores.
- Maternal diabetes is also an important cause of neonatal hypoglycaemia.
- Plasma concentrations of metabolic intermediates may be difficult to interpret in very low birthweight babies, due to a naturally impaired ketotic response. These babies also often have disproportionately high activities of circulating insulin. The most reliable indication of inappropriate hyperinsulinism is the glucose infusion rate required to maintain normoglycaemia. Usually this does not exceed 10 mg/kg/min
- Urine sugar analysis must be interpreted with caution. Children with a carbohydrate intolerance will only have an increased urinary excretion if there has been recent ingestion.
- Ketonuria is not a reliable guide to the the presence of ketosis: ketosis can occur when urine strip tests for ketones are negative. This may occur when there is a relative predominance of 3 hydroxybutyrate over acetoacetate as a result of the hepatic redox state and/or intracellular acidosis.