What Your CBC Blood Test Results Say About Your Health

female doctor taking blood sample
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A CBC, also known as a complete blood count, is a blood test commonly performed before and after surgery. This test measures the types of blood cells that are in your blood and how many appear, allowing your provider to see if your blood is normal or if there are signs of a problem.

The CBC is very useful because it can indicate many different common problems that occur in surgery patients during surgery and during their recovery. For this reason, a CBC may be drawn prior to surgery to "establish a baseline" for comparison with labs drawn after surgery. This way, it will be more obvious if there is a large change after surgery, or if something very serious like bleeding is happening during the hours and days after surgery. This test may reveal signs of infection, dehydration, anemia, the need for a post-surgery transfusion and even chronic conditions, such as blood cancers. 

While these tests are often done before and after surgery, they are also done frequently as part of a routine physical when there is no apparent health problem. This is considered a screening, and is done to catch problems in the early stages, before they become serious. A CBC is one of the most common blood tests done in healthcare, and is almost always a part of routine blood work.

How a CBC is Done

Blood can be drawn from a vein, or if you have a special IV inserted for surgery, it may be drawn from that line. Blood is typically drawn from a blood vessel directly into a special type of test tube, which is then sent to a lab for processing.

Abnormal Values

Keep in mind that "normal" values can vary slightly based on simple changes such as the elevation at which you live. The information and potential diagnosis listed for high and low levels in the following paragraphs is just a list of possible causes--it doesn't mean you have any of these problems. Do not assume anything about your blood tests without speaking to your provider as interpreting the results is both an art and a science and this article cannot replace the extensive education that providers receive.

Red Blood Cell Count (RBCs)

Red blood cells carry oxygen to the body.

Normal Values:

Men: 4.7 to 6.1 million cells per microliter.

Women: 4.2 to 5.4 million cells per microliter

Low results can indicate blood loss, problems with the bone marrow, leukemia and malnutrition. High results can indicate heart problems, kidney disease, over transfusion and dehydration.

White Blood Cell Count (WBCs)

These cells are the infection-fighting portion of the blood and play a role in inflammation.

Normal Values: 4,500 to 10,000 cells/mcl

A low count can indicate bone marrow problems or other issues preventing the body from making enough of these blood cells, chemical exposure, autoimmune disease, and problems with the liver or spleen. High levels can indicate the presence of tissue damage (burns), leukemia and infectious diseases.

Hematocrit

This is the percentage of the blood that is composed of red blood cells.

Normal Values:

Men: 40.7% to 50.3%

Women: 36.1% to 44.3%

Low hematocrit levels can indicate anemia, blood loss, bone marrow problems, malnutrition and more. High levels can indicate dehydration, polycythemia vera, smoking, living at a high altitude and heart diseases that are present at birth.

Hemoglobin

Hemoglobin is a protein on red blood cells that carries oxygen. Too few red blood cells is called anemia.

Normal Values:

Men: 13.8 to 17.2 grams/deciliter

Women: 12.1 to 15.1 grams/deciliter.

Low levels may indicate blood loss, caused by trauma, surgery, injury or possibly a long term but small amount of bleeding in the body, such as an ulcer in the stomach. It can also indicate an inability to make enough blood, which is often caused by a deficiency in iron, B12 or folate.

Platelet Count (thrombocytes)

Platelets are the part of the blood that makes the blood clot.

Normal Values: 150,000 to 400,000 per mm3.

Low levels may indicate the person is receiving chemotherapy, hemolytic anemia, the presence of a replacement heart valve, leukemia or a recent blood transfusion. High levels can be caused by anemia, specific types of cancer, polycythemia vera, a recent surgery to remove the spleen and other health issues.

A Word From Verywell

The CBC is a very useful test, but not as easy to interpret as you may believe, as there are many things to take into account when determining if there is a problem and what should be done about it. For example, a lower hemoglobin after surgery than before may indicate blood loss, but it takes a full understanding of the procedure that was done to know how much blood loss likely occurred during surgery, and if the changes on the labs indicate a major problem or a routine recovery.

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