Blood glucose i.e. blood sugar

Blood sugar is the plasma glucose level taken either as a venous blood sample or capillary sample from a fingertip.

In a laboratory the blood sugar level is measured from a blood sample, and the result is given as the plasma glucose level (P-gluk, fasting glucose abbreviation fP-gluk). In blood sugar self-monitoring, the samples are normally taken from a fingertip, in which case it is a capillary sample. The blood sugar limit values are slightly different for laboratory tests compared to self-monitoring tests from the fingertip.

Units of blood sugar

In Finland and Europe in general, the unit used for blood sugar is mmol/l. However, in the United States and some other countries, the unit used is mg/dl. The conversion factor between the units is 18. For example, if the blood glucose in the unit used in Finland is 5.6 (mmol/l), it can be converted to mg/dl by multiplying by 18, i.e. 5.6 x 18 = 101 mg/dl. Similarly, if the blood sugar in the US unit of measurement is 180 (mg/dl), it can be converted into mmol/l by dividing it by 18, i.e. 180 / 18 = 10 mmol/l.

This information may be needed, for example, if a person moving to Finland, from for example from the United States, needs to learn to understand blood glucose readings in a new unit of measurement.

Hint

The UK Diabetes Federation has a handy calculator to help with the conversion of the units of blood sugar.

Blood Sugar Converter (diabetes.co.uk)

Normal blood sugar

A healthy person’s morning blood sugar level after a fast (a minimum of 10 hours without eating) is 4,0–6,0 mmol/l (millimol in litre).

After a meal, the blood sugar level does not usually increase more than 2–3 mmol/l compared with the level before the meal. When blood sugar is tested from the fingertip, for a healthy person, it remains under 8,9 mmol/l.

In a glucose tolerance test, where person drinks a glucose solution containing 75 g of sugar, the blood glucose level measured by a laboratory blood test remains under 7,8 mmol/l after two hours from drinking the glucose solution.

Impaired blood glucose regulation

If your blood sugar rises too high without exceeding the diabetes limit, it is a case of impaired glucose regulation, also called pre-diabetes. It entails:

high fasting blood sugar, where the blood sugar level range is 6,1–6.9 mmol/l after fasting

and

impaired glucose tolerance, where the blood sugar in the venous blood sample level in glucose tolerance test is 7,8–11,0 mmol/l after 2 hours from drinking the 75 g solution of sugar.

In the fingertip capillary blood sample, the impaired glucose tolerance range is 8,9–12,1 mmol/l.

Blood sugar level in diabetes

You have diabetes if

your morning blood sugar level after a fast (fP-gluk i.e. fasting plasma glucose) measured in a laboratory is ≥ 7,0 mmol/l on at least two different days

if your blood sugar level in a venous sample in a glucose tolerance test is over 11,0 mmol/l 2 hours after drinking 75 g glucose solution. For a fingertip capillary sample, the diagnostic limit of diabetes is 12,2 mmol/l.

In theory, it is enough to diagnose diabetes in a person with the classic high blood sugar symptoms of increased urinary excretion and thirst, involuntary weight loss and fatigue, if the result of the venous blood test is 11,1 mmol/l or more once, regardless of the time of the test. Even then, the diagnosis is verified with a new test.