There are minor differences in arterial, venous and capillary blood glucose(CBG) levels but these do not cause practical treatment difficulties in the ED.

Capillary blood samples are not reliable when the circulation to the area is impaired e.g. in shock, and when the haematocrit is low. In these circumstances venous or arterial samples are preferable.

If there is any doubt, or the result does not fit with the clinical picture, the test should be repeated and a laboratory sample sent.

In patients with normal circulation, point of care capillary blood glucose measurements are reliable, providing the equipment is used according to the instructions, within the approximate range 4-10 mmol/L. In the setting of diabetes this provides results we can act upon as glucose levels below 4 mmol/L indicate hypoglycaemia and need treatment.

Learning Bite

In non diabetic patients hypoglycaemia should only be diagnosed on the basis of clinical symptoms and a serum or plasma glucose measured in the laboratory.