| Analyte | Tube Type/Colour | No. of Tubes | Test Code | Notes |
|---|---|---|---|---|
| Glucose | Fluoride - Grey |
1 |
SGLU |
|
|
Insulin Growth Hormone Cortisol Beta Hydroxybutyrate (ketones) C-Peptide |
PST - Light Green Micro PST |
1 2 |
INSX HGH COR OHB CPSN |
|
|
Proinsulin Sulphonyl Urea Insulin Analog Test Insulin Antibodies |
Plain - Red Micro Plain |
2 3 |
GHYP |
Serum is to be separated and divided into 4 aliquots, frozen, and stored. If requested by a Pathologist, activate testing by adding the appropriate test code. The samples will be discarded after 3 weeks. |
The Fasting Hypoglycemia Test is performed by the Dept. of Endocrinology
The patient is fasted under observation for up to 72h , with frequent blood glucose checks and monitoring for symptoms of hypoglycemia. The following bloods are taken during hypoglycemia:
NOTE:
The tests in the last row are only rarely required and will not be performed unless specifically authorised by a chemical pathologist. Clinicians should contact the on-call chemical pathologist via email ( chemicalpathologist@adhb.govt.nz ) or Lablink (ACH ext 22000 or from outside 09-3078995).
Tests which do not need to be taken during hypoglycemia:
sulphonylurea drug screen
acylcarnitines (in children) : plain (red) tube
Interpretive notes
Cortisol and growth hormone should be elevated during hypoglycemia as part of the normal counter-regulatory response. The absence of elevated levels suggests the possibility of pituitary or adrenal disease.
A ketotic response (raised BHB) should be present if hypoglycemia is not due to hyperinsulinism. However, the full ketone response develops gradually over a few hours of fasting; it may not be present if hypoglycemia is of acute onset.
C-peptide helps to distinguish between exogenous insulin (low C-peptide) and endogenous insulin (high C-peptide).
Acylcarnitine profile: This can be performed on plasma (1.0 mL in a plain or heparin tube) or a blood spot on a Guthrie card. It is the most important test if a metabolic disorder is suspected, and should be performed on all children presenting with unexplained hypoglycaemia. A sample taken when the child is not hypoglycaemic is equally diagnostic.
Raised lactate is a feature of Type 1 Glycogen Storage Disease (glucose-6-phosphatase deficiency).
Glucagon response
A robust rise in blood glucose (>1.5 mmol/L) following intravenous glucagon given during hypoglycaemia suggests that the hypoglycaemia is due to hyperinsulinism. This is because insulin promotes glycogen storage; stores will be depleted if hypoglycaemia is not due to hyperinsulinism.
