There are many reasons why you may need to have a blood test. But it’s worth remembering that there are some limits to what a blood test can tell you about your health.
Common blood tests may include something called a complete blood count (FBC), sometimes also called a complete blood count (CBC). It is used by your doctor to establish the number, size and other details of red blood cells, white blood cells and platelets – which play major roles in blood clotting in your system.
However, the title of the test may mislead people, who may believe that it is a complete, comprehensive indication of your health status.
Dr Carol Cooper, GP, media doctor and medical journalist, explains that there is no test that can tell you there is nothing wrong with a person.
“You can take a fistful of blood and still not do it,” she says.
Instead, if your complete blood count indicates that a certain blood cell is abnormally high or low, it may indicate infection, anemia, or other serious illnesses. Depending on the results, your doctor may request more tests to confirm the diagnosis.
What is normal blood count?
The normal limits of a complete blood count can vary, depending on factors such as your age, gender, and whether you have other health conditions.
There are many things the FBC measures, but in general, it includes the results of these tests with normal ranges:
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white blood cell count (WBC) – 4,000 to 10,000 cells per microliter (mcL) (4.0 – 10 x109/l).
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red blood cell count (RBC) – 4.0 to 5.4 million cells per mcL (4.0-5.4 x1012/L) for women or 4.5 to 6.1 million cells per mcL (4.0-6.1 x10)12/l)f or male.
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The average size (MCV) of your red blood cells – 80 to 100 femtoliter (FL).
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platelet count – 150,000 to 400,000 cells per mcL (150 – 400 x109/l).
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Mean Platelet Size (MPV) – 7.0 fl to 9.0 fl.
Can cancer be detected by a complete blood count?
Complete blood count results can help diagnose cancer:
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having fewer red blood cells than normal – May be a sign of anemia. This is not usually caused by cancer, but it is a possible sign of bowel or stomach cancer.
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too many white blood cells (Leukocytosis) – Very rarely this may be a sign of leukemia, which is a type of blood cancer.
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too many platelets (Thrombocythemia) – This is associated with an increased chance of getting cancer somewhere in the body, although this is not confirmed.
Other common tests
Other routinely ordered tests include measuring kidney or liver function, blood glucose (sugar levels), or hormone tests, most commonly thyroid hormones. Increased readings on ESR and other tests called CRP indicate that there is inflammation going on somewhere—which could be caused by anything from a mild viral infection to an autoimmune condition like rheumatoid arthritis or even, rarely, cancer.
However, these are different from a complete blood count. Doctors also frequently test vitamin D levels in the blood, as many people become deficient in this so-called sunshine vitamin during the winter months. It is available only in some parts of the country. Cholesterol testing is also commonly used to measure levels in the blood and can provide useful information about a person’s likelihood of having a heart attack or stroke.
If you have been sent for a blood test for the first time, you may feel anxious. Rest assured, this is a very straightforward process, often taking less than a minute to do.
Blood is usually taken at a GP practice or your local hospital. Usually a nurse or phlebotomist will draw blood from your inner arm using a needle. For most, the process is not painful, and only lasts a short time.
To help blood flow, the nurse will often tie a band over your arm, and may ask you to clench and release your fist.
When your doctor orders the test it is important to ask if it is a fasting test. If so, you should not eat or drink anything except water for 8-12 hours before as this may affect the test results. Check the timing with your doctor.
Some people may welcome the idea of a blood test and the information or potential reassurance it may provide. Others may feel worried or apprehensive about the possible results if the doctor requests a blood test after the consultation.
It is important to remember that a blood test will only give a snapshot of your levels based on the test requested, and cannot provide complete assurance of general health.
Also, while some blood tests can flag significant problems, blood tests are routine and scheduling the test does not indicate that your doctor suspects something serious.
In fact, when you are sent for testing, you will have already gone through two stages of diagnosis that are just as important as measuring the levels in the blood.
Cooper explains that the doctor will initially talk to you to find out about your symptoms and lifestyle. They will then examine you for additional clues as to what may be causing your symptoms.
She adds, “Requesting a blood test is only part of the screening process – but tests are just tests, they don’t give the whole picture.”
If you are concerned about why the test has been ordered or you want more information about your health status, it is important that you talk openly with the doctor during your appointment. To help, it’s worth writing down a list of symptoms and concerns before making an appointment.
We all are worried about our health from time to time. But for some people these worries become overwhelming. It is not uncommon for people to request a blood test for reassurance, or to worry about symptoms despite a doctor’s examination.
It is important to remember that blood tests cannot provide complete assurance about the state of your health, and trust your doctor to decide whether testing is needed.
If you find that you are becoming overly concerned about your health, or about the blood tests you have scheduled, talk to your doctor. They will be able to provide support and guidance.
