Blood test

What is a blood test?

A blood test involves taking a small sample of your blood for testing in the lab.

Your doctor or nurse may take your blood sample, or sometimes a phlebotomist (someone who is trained to take blood samples) will perform the test. You can have your blood test done at the hospital or at your local general practice clinic.

How is the blood collected?

Your blood will be drawn through a needle which is inserted through your skin into a vein. The most common places to draw blood are from a vein on the inside of your elbow or a vein on the back of your hand since your veins are closer to the surface there.

A tight band (tourniquet) is placed around your arm just above the area where the blood will be drawn. This brings the vein closer to the surface of the skin, making it easier to collect the blood sample. The area will be cleaned with an antiseptic wipe or cotton swab before the test is performed.

The needle is usually attached to a syringe or a plastic device called a vacutainer and the blood is placed in a blood collection container called a vial so that once the blood sample is taken it can be easily sent to a laboratory doctor for analysis. Vials often contain small amounts of chemicals that prevent blood from clotting during transport.

Collecting a blood sample usually only takes a few minutes.

Does a blood test hurt?

You may feel a slight tingling sensation as the needle enters your skin, but it shouldn't be painful.

If you don't like the needles, tell the person taking the sample so they can reassure you. If you feel anxious about your blood test, ask a family member or friend to come with you. You may be able to apply a numbing cream to the area before you get tested, but this will take some time to be effective, so it may be a good idea to apply it before you get tested.

Rarely, some people feel dizzy during a blood test. This is more likely to happen if you're dehydrated, so try drinking some water before having your blood test. Tell your doctor or health care professional if you tend to pass out before the test, as they may suggest that you lie down while your blood is drawn.

What happens after a blood test?

After the sample is taken, you will be asked to apply pressure to the area for a few minutes. You can remove any bandage as soon as you feel able.

You may still have a small bruise or swelling where the needle went into your skin, but this is nothing to worry about and should go away in a few days.

Different types of blood tests.

The most common types of blood tests used to assess heart disease are:

• Cardiac enzyme tests (including troponin tests): help diagnose or rule out a heart attack.

• Complete blood count (BCF): measures different types of blood levels and can show, for example, if there is an infection or if you have anemia.

• Thyroid function tests: These show whether you have an underactive or overactive thyroid gland, which produces a hormone called thyroxine. If the levels are abnormal, they may be linked to certain heart conditions and symptoms related to slow or fast heartbeat or palpitations.

• Lipid profile: measures the cholesterol level and the distribution of good and bad fats present in the blood.

• Liver tests: The liver is a vital organ with many functions. This test gives a breakdown of liver function, which if not working well can have a huge impact on the rest of the body.

• Coagulation test: measures the rate at which blood clots. This is important if you are taking blood thinners like warfarin.

• BNP (B-type natriuretic peptide) tests: These show the level of a hormone in the blood, which, if high, may be a sign of heart failure.

• U and Es test: represents urea (a protein found in the blood) and electrolytes, which measure the levels of sodium, potassium and other important chemicals in the blood, such as magnesium and calcium. These chemicals are important for the general functioning of your heart and also help assess kidney function. Imbalances in the blood may be related to medications you are taking.