Does a complete blood count (CBC) test require any special preparation?

Usually, a complete blood count (CBC) test does not require any special preparation on your part. You may eat and drink normally before the test [1].

However, if your healthcare provider has requested additional blood tests at the same time as the CBC sample collection, you may need to fast (refrain from eating and drinking) for several hours before the test. Your doctor will inform you if there are any special instructions to follow [1].

What is a complete blood count (CBC)?

A complete blood count is a set of blood tests that measures the number and size of various types of cells in your blood. This test includes measuring red blood cells that carry oxygen, white blood cells that fight infection and disease, and platelets that help stop bleeding by clotting the blood [1].

The test also measures hemoglobin, an iron-rich protein in red blood cells that carries oxygen, and hematocrit, which is the proportion of red blood cells in the total blood volume, in addition to the mean corpuscular volume (MCV) [1].

Why might you need a CBC test?

A complete blood count is a common part of a comprehensive routine examination. It is also used to monitor certain health conditions or treatments that may affect blood cell counts, such as infection, anemia, immune system disorders, and blood cancers [1]. Your healthcare provider may order it to help diagnose blood diseases, infections, immune system disorders, or other medical conditions, or to check for changes in a pre-existing blood disorder [1].

What happens during the test?

A healthcare professional will take a blood sample from a vein in your arm using a small needle. After inserting the needle, a small amount of blood will be collected into a test tube or vial. You may feel a slight pinch when the needle goes in or out. This process usually takes less than five minutes [1].

Are there any risks to the test?

There are no significant risks to having a blood test. You may feel slight pain or notice a small bruise at the site where the needle was inserted, but most of these symptoms disappear quickly [1].

Understanding results and next steps

A complete blood count is just one tool your doctor uses to evaluate your health. If any of your values are abnormal, it does not always mean you have a medical condition requiring treatment. Factors such as diet, activity level, medications, menstrual cycle, and not drinking enough water can affect the results [1].

It is important to discuss your results with your healthcare provider to understand their implications in the context of your medical history, symptoms, and other factors. You may also need additional tests to confirm a diagnosis or determine the cause. For more information on interpreting CBC results, you can visit Complete Blood Count Tests: Reading Results and Understanding Their Health Implications (Arabic).

For example, a high platelet count (thrombocytosis) may indicate an infection or inflammation, or even some types of cancer such as lung or gastrointestinal cancer [2]. In rare cases, a high platelet count may be the first sign of cancer [2]. If you suffer from symptoms such as chronic headaches, dizziness, or burning pain and tingling in the hands and feet, especially with a high platelet count, it may indicate the formation of blood clots [2]. In these cases, it is essential to consult a doctor to evaluate the situation and determine if treatment is needed to prevent serious complications such as a stroke or heart attack [2].

Medical references

• Complete Blood Count (CBC)
• Platelet Disorders Thrombocythemia and Thrombocytosis