Glucose - plasma, serum, or whole blood

Last updated: Thursday, 25, March, 2010

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Item Process

5 mL blood in fluoride-oxalate tube is the preferred specimen.

Collection in plain or lithium heparin tubes is only satisfactory if the specimen is delivered promptly to the laboratory.


Spectrophotometry; glucose-specific electrode.

Reference Interval

Venous plasma or serum
Fasting: 3.0-5.4 mmol/L
>2 hour post-prandial
'Random': 3.0-7.7 mmol/L.

(whole blood meters are now routinely calibrated to give plasma equivalent results)

Detection of hyperglycaemia and hypoglycaemia.

Diagnosis and as a screening test for diabetes mellitus.

Monitoring glycaemic control.

See also Glucose test strips - blood.


In a patient with symptoms suggestive of diabetes mellitus, the finding of a fasting plasma glucose of >7.0 mmol/L, or a plasma glucose of >11.1 mmol/L at least two hours following a meal, is diagnostic of diabetes mellitus. The finding of either of these levels on two occasions, even in the absence of symptoms, is also diagnostic of diabetes mellitus.

In patients with fasting plasma glucose levels between 5.5-6.9 mmol/L or random plasma glucose levels between 7.8-11.0 mmol/L, an oral GTT should be performed if the patient is at high risk for diabetes.

Irrespective of any GTT results, a fasting plasma glucose 6.1 – 6.9 mmol/L indicates Impaired Fasting Glucose.

Fasting plasma glucose levels <5.5 mmol/L and/or random levels <7.8 mmol/L make diabetes mellitus unlikely, and a GTT is not indicated.


Rumbold AR and Crowther CA. Aust N Z J Obstet Gynaecol  2001; 41(1): 86-90.

Colman PG et al. N Z Med J 1999; 112(1086): 139-141.

RCPA - AACB Position Statement on IFG. Pathology, 2008;40:627-8.