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Blood tests

Information on having blood tests and the types of blood tests you might have.

Blood tests can:

  • check your general health, including your liver, kidneys and heart function
  • check numbers of blood cells
  • help diagnose cancer and other conditions

Your blood sample is sent to the laboratory. A blood doctor can look at your sample under a microscope.

They can see the different types of cells and can count the different blood cells. They can also test for different kinds of chemicals and proteins in the blood.

Preparing for your blood tests

You can eat and drink normally before most blood tests. For fasting blood tests you need to stop eating and drinking beforehand. Your doctor will tell you for how long.

What happens

You sit or lie down to have the test.

A nurse or person specialised in taking blood (a phlebotomist) chooses the best vein to use. This is usually from your hand or arm. 

They put a tight band around your arm above the area where they take the sample. Then they put a small needle into your vein. Next, they attach a syringe or small bottle to the needle to draw out some blood. They might fill several bottles.

Once they have all the samples, they release the band around your arm. Then they take the needle out and put a cotton wool ball or small piece of gauze on the area. Pressing down on the cotton wool or gauze for a few minutes helps to stop bleeding and bruising.

Look away when they’re taking the blood if you prefer. Tell your nurse or phlebotomist if you feel unwell.

Getting your results

Ask the phlebotomist or your doctor or nurse when you will get your results, and who will give them to you.

Some results might be available quickly, for example full blood count results.

Some other tests might take several weeks.

Possible risks

Blood sampling (phlebotomy) is a safe test. There is a possibility of:


You can bleed if you’re taking medicines to thin your blood (anticoagulants) such as aspirin. Pressing hard when the needle is removed helps to stop it.


Sometimes blood leaks out of the vein and collects under your skin. This can look like a small dark swelling under the skin (haematoma).

Pressing hard once the needle is removed can help.


The site of the test can be tender for a few minutes. Tell the person taking the blood if you have a tingling or shooting pain.

Swelling (oedema)

You should avoid whenever possible having blood taken from an arm that is swollen or has a risk of swelling: for example, after surgery or radiotherapy to the lymph nodes on that side. Ask your nurse to use the opposite arm to take the sample.

Types of blood tests

Full blood count

A full blood count measures the number of red cells, white cells and platelets in your blood.

  • Red cells carry oxygen around our bodies. Haemoglobin is the part of the cell that carries oxygen. If you have a low red cell count, your doctor might say you’re anaemic (pronounced a-nee-mic). This can make you feel tired, short of breath and dizzy.
  • White cells fight infections. There are several different types of white cells, including neutrophils and lymphocytes.
  • Platelets help clot the blood. Symptoms of a low platelet count include abnormal bleeding, such as bleeding gums and nosebleeds.

There isn’t an exact range of normal for blood counts. The range of figures quoted as normal varies slightly and also differs between men and women.

Table showing the normal values of men and women

Urea and electrolytes

These blood tests show how well your kidneys are working. Urea is a waste chemical produced from digesting protein.

Our kidneys remove urea from the blood and get rid of it in the urine.

Electrolytes are substances such as sodium, potassium, chloride and bicarbonate.

Liver function tests (LFTs)

Liver function tests (LFTs) check how well your liver is working. LFTs look for levels of enzymes and proteins made by the liver. They include:

  • alanine aminotransferase (ALT)
  • aspartate aminotransferase (AST)
  • alkaline phosphatase (ALP)
  • gamma-glutamyl transferase (Gamma GT)

They might be raised if you have a blockage in your liver or bile duct, or if you drink a lot of alcohol.

LFTs also look at the amount of bilirubin in the blood. This is a chemical in bile. 

Bilirubin can be raised if you have a problem with your liver or gallbladder. Bilirubin can cause yellowing of your skin and eyes (jaundice). 

LFTs also measure albumin. This is a protein in the blood that can be low in some types of cancer. You can also have low albumin if you’ve been eating small amounts and are malnourished.

Tumour markers blood test

Tumour markers are substances that either the tumour or your body produces as a response to a cancer. They’re usually proteins.

Some tumour markers are only produced by one type of cancer. Others can be made by several types. Some markers are found in non cancerous conditions as well as cancer.

Doctors might use tumour markers to help diagnose a cancer.

More information

We have more information on tests, treatment and support if you have been diagnosed with cancer.

Information and help

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