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Blood tests

Get information on having blood tests. A blood test can help measure how well your kidneys are working. 

Blood tests can:

  • check your general health, including how well your liver and kidneys are working
  • check numbers of blood cells
  • help diagnose cancer and other conditions

Your blood sample gets sent to the laboratory. Specialist technicians and doctors 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.

Types of blood tests

Full blood count (FBC)

A full blood count (FBC) 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 between laboratories and also differs between men and women.

A FBC will tell your doctor if the blood in your urine is affecting your level of red blood cells going around your body. 

Diagram of table showing the normal values of men and women

Urea and electrolytes information

These blood tests show how well your kidneys are working. Waste chemicals called urea and creatinine are produced by the body. Our kidneys remove them from our blood and get rid of them in our 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 or which are cleared 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.

In bladder cancer an increased level in ALP could mean the bladder cancer has spread to the bones. Usually your doctor would also send you for a bone scan to check for this. 

Glomerular filtration rate (GFR)

You might have this test to measure how well your kidneys are working and how quickly they remove waste products from the blood. You have an injection that contains a dye. Then you have a number of blood samples taken over a few hours to show how well the kidneys are filtering out the dye.

You might have this test if you need chemotherapy treatment.
 

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 doctor, nurse or phlebotomist (person specialised in taking blood) chooses the best vein to use. This is usually from your arm or hand. Let them know if you are afraid of needles, get unwell with the sight of blood or are allergic to plasters or latex. 

They put a tight band (tourniquet) around your arm above the area where they take the sample. You may need to clench your fist to make it easier to find a vein.

They clean your skin and then put a small needle into your vein. Next, they attach a small bottle or syringe to the needle to draw out some blood. They might fill several small bottles.

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

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

Getting your results

Ask the phlebotomist, doctor or nurse when and how you will get your results. Some results might be available quickly, such as a full blood count. But some other tests might take several weeks.

Possible risks

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

  • bleeding and bruising - pressing hard when the needle is removed can help to stop it
  • pain - this is normally mild and can last for a few minutes
  • swelling (oedema) - ask your nurse, doctor or phlebotomist to avoid an arm that is swollen or has a risk of swelling
  • feeling faint or fainting - tell the person doing your blood test if you're feeling lightheaded or dizzy at any time
  • infection - this is very rare
Last reviewed: 
07 Jun 2019
  • Oxford handbook of clinical medicine (10th edition)
    M Longmore and other
    Oxford University Press, 2017

  • Bladder cancer: overview and disease management. Part 1: non-muscle-invasive bladder cancer
    B Anderson
    British Journal of Nursing, 2018. Volume 27, Issue 9, pages 27 – 37

  • Bladder cancer: ESMO Practice Guidelines for diagnosis, treatment and follow-up
    J Bellmunt and others
    Annals of Oncology, 2014. Volume 25, Issue 3, Pages 40-48

  • BMJ Best Practice. Bladder Cancer
    D Lamm
    BMJ Publishing Group, (Updated June 2018)

  • The Royal Marsden Manual of Clinical Nursing Procedures (9th edition)
    L Dougherty and S Lister
    Wiley Blackwell, 2015

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