Blood Tests

What it involves

A blood test examines a sample of blood in a laboratory to measure substances such as blood cells, sugar, cholesterol or markers of organ function. A trained clinician takes the sample from a vein, usually in the arm, with a small needle.

Who it is for

Blood tests are used to help diagnose conditions, monitor long-term conditions and check general health. A doctor chooses the tests according to your symptoms and history. Some tests are available without a request in some places.

How long it usually takes

Taking the sample takes a few minutes. Results can take from hours to several days, depending on the test.

What to expect

You may be asked to fast for some tests, and the clinic will tell you if so. The clinician cleans the skin, applies a tourniquet and takes the sample. You may feel a sharp scratch. Pressure on the site after helps prevent bruising.

Aftercare

Keep a plaster on for as long as advised and avoid heavy lifting with that arm for a short while. Tell the clinician if you feel faint during or after the test. Ask how and when you will receive results, and who will explain them.

When to seek it

Have a blood test when your doctor advises it, as part of a health check or to monitor a condition. A test result should be interpreted by a doctor who knows your history.

What affects the cost

Cost depends on the tests requested, whether they are sent to an outside laboratory, urgency and any consultation to explain results. HealthNaro shows a price only where a clinic has supplied a figure with a source and date.

Read more in our guide: Blood tests: how they are done, how to prepare and how to read your results.

This page is general information and not medical advice. In an emergency, contact your local emergency number.

Sources: NHS; World Health Organization.