What is a complete blood count test, and when do doctors recommend getting it done?

After learning how to read the report of a ‘lipid profile’ test and a ‘routine and culture blood (or stool)‘ test, let’s deep dive into a ‘complete blood count’ test. Commonly known as CBC, it encompasses an investigation of hemoglobin, white blood cell count, and platelets. It also includes other parameters that indicate the nature of the red blood cells, white blood cells, and platelet morphology. But that’s not all, according to Dr Suchismitha Rajamanya, lead consultant and HOD, internal medicine, Aster Whitefield Hospital, Bengaluru a CBC further includes a differential count, which provides information about the proportion of the various types of white blood cells, such as neutrophils, lymphocytes, monocytes, and eosinophils.

“A complete blood count cannot be performed without including all these vital parameters. We can request separate tests for hemoglobin, white blood cell counts, and platelets. However, a complete blood count encompasses all of these tests. White blood cells are essential for helping the body fight against infections and maintaining immunity. Typically, when we have a bacterial infection, the white blood cell count tends to increase. In contrast, during a viral infection or sometimes even in typhoid infection, their count shows a decreasing trend,” explained Dr Rajamanya.

In certain cases of leukemia or lymphoma, the white blood cell count can increase tremendously or decrease significantly. Based on the white blood cell and the differential counts, experts consider many differential diagnoses, which help evaluate a patient further.

Some symptoms such as fatigue, weakness, fever, inflammation, bruising, and bleeding may require doctors to suggest CBC for their patients. It may also be advised for general health monitoring during routine checkups or treating chronic conditions. “In contrast, a doctor may suggest a White Blood Cell (WBC) count test when specifically assessing for infection or inflammation, monitoring immune-related conditions or treatment efficacy, or during post-surgical or trauma recovery,” said Dr Rajamanya.

Here’s what doctors suggest (Source: Getty Images/Thinkstock)

For a layperson, interpreting a CBC report can be challenging. “A non-medico can read the report as nowadays most reports come with the normal range of values. But what a non-medico should not do is self-diagnose or Google search his or her findings based upon the report. There are a lot of things which go into the interpretation of a report beyond the normal values,” cautioned Dr Pruthu Dhekane, consultant infectious disease, Manipal Hospital, Baner, Pune.

Certain other parameters apart from absolute cell counts help give a head start direction for evaluating a suspected disease. “In short, we can say that a CBC is a vital diagnostic tool that provides essential information about a person’s health. Abnormal results should prompt immediate medical consultation to determine the underlying cause and appropriate treatment,” said Dr Arora.

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