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A routine blood test may seem like a simple health check, but it can sometimes reveal several important clues. A complete blood count (CBC) measures red blood cells, white blood cells and platelets, and is one of the most commonly performed blood tests. While it is not designed specifically to detect cancer, changes in these blood components can sometimes be among the earliest signs of a blood-related disorder. In some cases, leukaemia and other bone marrow disorders may cause abnormalities in blood counts before a person develops other symptoms.
Dr Rahul Bhargava, Principal Director & Chief - Hematology, Hemato Oncology & Bone Marrow Transplant, Fortis Memorial Research Institute, Gurgaon, says that unexplained changes in a CBC should not be ignored, especially when they persist or worsen over time. "What becomes clinically important is a pattern that is persistent, unexplained, or progressively worsening," said Dr Bhargava.
However, an abnormal blood count does not automatically mean cancer. Infections, nutritional deficiencies, inflammation, medicines and several other conditions can also affect blood counts.
What Can A CBC Reveal?
A CBC gives information about three major types of blood cells: red blood cells, white blood cells and platelets. Changes in any of these can be a sign that further evaluation is required. In blood cancers such as leukaemia, the bone marrow may start producing abnormal blood cells. This can disturb the normal balance of healthy blood cells and lead to unusual CBC results. Some changes that may need attention include:
Unexplained increase or decrease in white blood cells: A significantly high or low white blood cell count can have several causes, but persistent or unusual changes may require further investigation.
- Persistent anaemia: A low red blood cell or haemoglobin level without an explanation can sometimes be linked to a problem affecting the bone marrow.
- Low platelet count: Platelets help the blood clot. A persistent drop in their numbers may need medical evaluation.
- Combination of abnormalities: Anaemia occurring along with low platelets or an abnormal white blood cell count may be more concerning.
- Abnormal or immature cells: Sometimes, a laboratory report may mention abnormal or immature cells in the peripheral blood.
What Happens After An Abnormal Blood Count?
If a CBC shows concerning changes, a doctor may first recommend repeating the test to confirm whether the abnormality persists. The next step may include a peripheral blood smear, in which a blood sample is examined under a microscope to look at the size, shape and appearance of blood cells.
Depending on the findings, a haematologist may recommend additional tests. These can include flow cytometry, which can help identify abnormal blood cell populations. Imaging may also be advised in selected cases. If there is a concern about a problem originating in the bone marrow, a bone marrow examination may be required. This allows doctors to directly examine the cells being produced inside the marrow and can help establish the cause of abnormal blood counts.
The exact tests depend on the person's CBC results, symptoms, medical history and physical examination. "When such abnormalities are identified, a haematologist may recommend repeating the CBC, reviewing a peripheral blood smear and, depending on the findings, conducting additional tests such as flow cytometry, imaging or a bone marrow examination," said Dr Bhargava.
Blood Cancer Can Have Subtle Signs
Some blood cancers can develop without obvious symptoms in their early stages. A person may not necessarily have severe fatigue, frequent infections, unexplained bleeding or other classic warning signs when a blood count first becomes abnormal. This is why persistent unexplained changes in routine blood tests should be discussed with a doctor. Early evaluation does not mean that cancer will be diagnosed, but it can help identify the actual reason behind the abnormal result.
At the same time, people should not panic after seeing a single abnormal number on their CBC report.
A complete blood count is a screening and diagnostic tool, not a cancer test. It cannot confirm blood cancer on its own. Its importance lies in helping doctors recognise patterns that may require additional investigation. An abnormal result needs to be checked along with other symptoms, medical history, examination and previous blood reports. If a blood count is persistently abnormal, unexplained or progressively changing, timely medical evaluation is important. "People should not be alarmed by an isolated abnormal blood count. The result needs to be interpreted in the context of the person's symptoms, medical history, examination and previous blood reports," added Dr Bhargava.
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