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Blood tests

You might have blood tests to help diagnose stomach cancer. 

Blood tests can:

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

Your blood sample is sent to the laboratory and a specialist looks 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 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.

Photograph of a blood test

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.

Types of blood tests

Full blood count information

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.

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.

Tumour markers blood test

As well as blood tests to check your general health, your doctor may test for cancer markers. Markers are chemical substances that can show up in the bloodstream in some types of cancer. 

For example, the markers CEA (carcinoembryonic antigen) and CA 19-9 (cancer antigen) are sometimes raised in stomach cancer, as well as other cancers. But some people with stomach cancer do not have raised levels in their blood and they can be raised in non cancerous conditions. 

If your tumour markers are raised at diagnosis, your doctor might check the levels again after treatment and as part of your follow up.

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: 
05 May 2018
  • Oxford handbook of clinical medicine (10th edition)
    M Longmore, IB Wilkinson, A Baldwin and E Wallin
    Oxford University Press, 2017

  • Cancer: Principles and Practice of Oncology (10th edition)
    VT DeVita , TS Lawrence, SA Rosenberg
    Lippincott, Williams and Wilkins, 2015

  • Gastric cancer: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up 
    E Smyth and others, 
    Annals of Oncology, 2016. Volume 27, Pages v38–v49

  • Biomarkers for gastric cancer: Progression in early diagnosis and prognosis (Review)
    Z Jin and others, 
    Oncol Lett, 2015. Volume 9, Pages 1502–1508.

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