Most standard laboratory tests do not require you to fast. When the tests are being arranged, remember to find out whether they require you to fast, i.e. eat nothing for 10 hours. Usually, a test that requires you to fast is indicated with the letter f (fasting) in the laboratory referral.
Going to laboratory tests
Before a lab visit, check if the planned tests require you to fast or take a sample before a specific time.
In terms of the normal follow-up tests of a person with diabetes, fasting is only required if the specific objective is to check your blood sugar or blood fat levels in the morning after a period of fasting. If you monitor your own blood sugar, the fasting blood sugar test is not normally necessary. You can also check your blood fat levels after light breakfast, unless a fasting test is specifically requested.
You do not need to fast for a glycated haemoglobin HbA1c test.
In the morning before the lab visit, you can take your normal tablets, unless you have been otherwise instructed by the care provider.
In other words, laboratory tests can in most cases be conducted in such a way that a person in insulin therapy can take their basal insulin as usual. In the case of multiple daily injections (MDI) therapy, you can have light breakfast in the morning and take a corresponding rapid-acting insulin dose.
If the test requires you to fast, you can take your normal day or evening basal insulin the day before. For example, the tests are due to take place between 07 and 09. You must fast for at least 10 hours before the tests, although you are allowed a glass of water in the morning.
You can eat breakfast and have the corresponding bolus insulin only after the laboratory tests are finished. If you normally take basal insulin in the morning, you can take it after the test. The same applies to your blood sugar tablets: you can only take them after the test.
If your blood sugar easily drops too low in the morning in the absence of nutrition, check that your basal insulin dose is not too high in the first place. If necessary, you can reduce the previous basal insulin dose by approximately 10–20% with a view to travelling to a laboratory or waiting for the test, for example. Bear in mind, though, that for some basal insulins (such as insulin glargine 300 units/mL or insulin degludec), there is a delay of several days before the effect of reducing the dose becomes evident.
For some laboratory tests, the sample needs to be taken at a specific time. For instance, the thyroid test P-TSH must be performed before 10 in the morning and before taking the potential thyroid medication.
Updated 25.5.2022