Glucose

Glucose can be measured in different sample types. However, the concentration of glucose in any sample begins to decrease immediately after collection because of the glycolytic action of red blood cells and white blood cells. For this reason, if there is likely to be any delay in sample analysis, eg a blood sample taken at a GP surgery and then transported to the main hospital laboratory, blood samples for measurement of glucose are collected into tubes containing fluoride oxalate (yellow top tube) to stop this occuring.

Another thing that you need to be aware of in interpreting glucose results is that values in plasma (lab measurement of glucose) are slightly higher (a bit over 10%) than in whole blood (point of care measurement from a glucose meter).


High glucose

High glucose is due to too little insulin or a resistance to its action.  This is called diabetes. Diabetes (Type 2) is common and should be screened for. See flowchart for high glucose.


Low glucose

A low glucose (biochemically defined as <2.5 mmol/L although symptoms of hypoglycaemia may occur at higher glucose levels) is usually due to an excess of insulin in a diabetic. If persistent occurrence and cause not clear then refer to Endocrinology.

Some possible causes of hypoglycaemia in adults are


Drugs - Insulin / sulphonylureas / alcohol - check glucose and insulin

Organ failure - Liver / Adrenal / Pituitary - check LFT, 9am cortisol, GH, TSH, fT4, LH,     FSH, prolactin

Reactive - refer to Endocrinology as may require prolonged GTT

Insulinoma / other tumour - rare - refer to Endocrinology