Understanding the Complete Blood Count

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Not everyone likes getting their blood drawn at the doctor’s. There’s a needle in the arm, it’s pumped into vials, and then sent off to a mysterious lab. What really happens there, and what do doctors look at to examine your blood and review your health? One of the most common blood tests done that will help answer this question is the Complete Blood Count.

The Complete Blood Count, or CBC test, that test that all the doctor’s on TV yell for. This test evaluates the proportions and patterns of different parts of your blood. CBCs are often ordered as a part of a routine check-up, because they provide a useful indicator of overall health. CBCs are also important because they detect abnormalities in blood composition, help to diagnose disease, and monitor progress of treatments or medications.

components of blood graphic

Analyzing a blood sample to obtain CBC results only takes a few hours. When blood is drawn from the patient, it is collected in a test tube that contains an anticoagulant, which prevents blood clots from forming in the sample. At the lab, dyes are added to identify different parts of the blood when the sample is put under a microscope. The counting and analysis of the blood is done automatically by a machine called a hematology analyzer.

A standard CBC includes a red blood cell count, which simply counts the number of these cells present in the given blood sample. CBCs evaluate red blood cells carefully because abnormalities in red blood cells play a large role in diagnosing diseases such as anemia and leukemia, which is cancer of the blood. CBC tests measure the physical attributes of red blood cells and analyze the amount of hemoglobin (a protein that carries oxygen) within the cells. An important part of the CBC is evaluating hematocrit, which measures the proportion of red blood cells relative to the volume of blood in the body. Low or high levels of hematocrit can signal dehydration, anemia, or problems with bone marrow, where red blood cells are created.

CBCs perform white blood cell counts and differentials, which tracks the proportions of different types of white blood cells. The white blood cell count of CBCs are used to detect infections, tissue damage, and autoimmune problems. CBC tests also count the number of platelets in the sample, which can be useful in predicting the risk of dangerous blood clots.

The Complete Blood Count test is a simple yet effective way for doctors to evaluate health and it can lead to more rapid and accurate diagnoses. Understanding how the CBC is done and how doctors use the results can make appointments and blood tests seem like a lot less of a mystery!

Mayo Clinic: https://www.mayoclinic.org/tests-procedures/complete-blood-count/about/pac-20384919
Scripps: https://www.scripps.org/news_items/6595-what-do-common-blood-tests-check-for
Leukemia and Lymphoma Society: https://www.lls.org/managing-your-cancer/lab-and-imaging-tests/blood-tests