Glucose (Plasma)

General Information

Glucose is a vital metabolic fuel in the body whose concentrations are maintained within narrow limits by the action of various hormones, namely insulin and glucagon.  Glucose measurements are used to screen for, diagnose, and monitor diabetic states. Measurements are also undertaken to investigate hypoglycaemic states associated with metabolic and other conditions in adults and children.

Patient Preparation

Please state on the form if fasting specimen.

Notes

Glucose levels decline significantly in whole blood in vitro unless an inhibitor of glycolysis is present. Samples for glucose measurement must therefore be collected into a fluoride oxalate (grey-top) tube, since the fluoride inhibits glycolysis. Also, blood glucose concentrations tend to be 10-15% lower than serum or plasma glucose concentrations, and therefore different diagnostic cut-offs apply. 

Reference Range

There is no associated reference range for plasma glucose as the concentration should be assessed in conjunction with the fasting and diabetes status. Diabetes mellitus can be diagnosed based on random and fasting glucose. Various cut offs are quoted in the literature however the most commonly used are based on the WHO recommendations (2006) which states with symptoms of diabetes symptoms one requires:

• A random venous plasma glucose concentration ≥ 11.1 mmol/l or
• A fasting plasma glucose concentration ≥ 7.0 mmol/l (whole blood ≥ 6.1 mmol/l) or
• Two hour plasma glucose concentration ≥ 11.1 mmol/l two hours after 75g anhydrous glucose in an oral glucose tolerance test (OGTT).

Gestational diabetes should be diagnosed if the woman has either:

• A fasting plasma glucose level of 5.6mmol/l or above or
• A 2-hour plasma glucose level of 7.8mmol/l or above.