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 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.
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 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.
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
Types of blood tests
Full blood count
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.
Urea and electrolytes
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.
If you have osteosarcoma, your doctor should measure your ALP level (alkaline phosphatase). This chemical is found in your blood and is a measure of bone activity. If you have a bone cancer, the levels of bone cell activity in the affected bone may be higher than normal. Not everyone with osteosarcoma has a raised ALP level.
For Ewings sarcoma your doctor should measure your LDH level (lactate dehydrogenase) as it may be raised and can affect the treatment you might have.