Does an abnormal blood test mean cancer?

You open the result and see a mark or red colour beside a few numbers. Your family doctor has said you should see a blood specialist. The first thought that comes to most people is cancer. If that is how you feel, know this first: your fear is natural. Many abnormal results have a cause other than cancer, but the cause has to be found.

What does a blood test measure?

The most common test, the complete blood count (CBC), counts the number and size of three groups of cells:

• Red blood cells and haemoglobin, which carry oxygen around the body
• White blood cells, which protect against infection
• Platelets, which help the blood clot

Each laboratory writes its own normal range on the sheet. Go by that range, not by a number from a book or the internet.

Why might a number be abnormal?

Sources say that if some levels are abnormal, it does not necessarily mean a disease that needs treatment. Diet, activity level, medicines, periods and dehydration also affect the result. A few examples:

• Low haemoglobin may be a sign of anaemia. The most common cause of anaemia is iron deficiency, and bleeding is its main cause, for example heavy periods. Vitamin deficiencies, long-term conditions such as kidney problems or inflammation, and bone marrow problems are causes too.
• A high white cell count is mostly related to infection or a reaction to a medicine, but sometimes it is a sign of a blood disease. If the number is very high or does not come down, show it to a doctor soon.
• A low white cell count may be related to an autoimmune disease, a bone marrow problem or cancer.
• A low platelet count has many causes: a bone marrow problem, destruction of platelets by the immune system, some medicines, infections, autoimmune diseases and an enlarged spleen. A mildly low platelet count often has no symptoms.

So an abnormal number is a “question”, not an “answer”.

How is cancer diagnosed?

The important point is that a blood test alone does not confirm cancer. The NCI says an abnormal blood test result is not a definite sign of cancer, and doctors use it together with a biopsy and scans. In blood cancers too, the blood count may raise suspicion, but to decide the type, a biopsy of the bone marrow or a lymph node is usually needed.

When is it more worrying?

The doctor looks more closely when:

• The abnormal number does not change on a repeat test
• There are symptoms such as fever for no reason, night sweats, severe tiredness, weight loss for no reason, repeated infections, easy bruising or bleeding, or an enlarged lymph node

These symptoms are seen in simpler illnesses too. Having them does not mean cancer, but it is a reason for a closer look.

About a lymph node, the NHS says the cause is usually a common infection and it settles within one to two weeks. If it is getting bigger, has not shrunk after a week, is hard and does not move, or comes with fever and night sweats, you should show it to a doctor. Rarely, the cause is a blood cancer or lymphoma.

What is the next step?

• Write down your symptoms and medicines so you can tell the doctor. Do not stop or start any medicine until the doctor says so.
• Find your earlier test results. The trend of the numbers matters more than a single number.
• If your family doctor has referred you to a blood specialist, do not put off the appointment, and take your papers. See the page “Your first visit”.
• Make a list of your supplements and medicines.
• Before the visit, do not diagnose yourself by searching the internet.

When should you get urgent help?

If, along with an abnormal test, you have bleeding that does not stop with pressure, sudden shortness of breath, chest pain, fainting or confusion, or if your white cell count is low and you have a fever, do not wait for an appointment. Call 115 (the emergency number inside Iran) or go to the emergency department.

Your test result must be interpreted by your treating doctor. This article only helps you ask better questions and be less afraid.