Leukemia is a cancer that begins in the blood-forming tissues of the body, specifically the bone marrow, involving the uncontrolled growth of abnormal blood cells. A complete blood count (CBC) is a common blood test used to assess overall health. It helps identify a wide range of conditions, including infections, anemia, and certain blood disorders. The central question often arises whether a CBC test alone can reliably detect leukemia.
What a Complete Blood Count Measures
A complete blood count (CBC) measures the different components circulating in a person’s blood. These include red blood cells, white blood cells, and platelets.
Red blood cells transport oxygen throughout the body. White blood cells are a central part of the immune system, fighting infections and foreign invaders. There are several types of white blood cells, each with specialized functions, including neutrophils, lymphocytes, monocytes, eosinophils, and basophils.
Platelets are small cell fragments that play a crucial role in blood clotting. The CBC provides counts of each of these cell types, along with measurements of hemoglobin and hematocrit.
How Leukemia Impacts Blood Cell Counts
Leukemia affects the production of healthy blood cells in the bone marrow, leading to abnormal counts of red blood cells, white blood cells, and platelets.
It can cause a significant increase in white blood cells, though these cells are often immature and do not function correctly. Leukemia can also lead to abnormally low white blood cell counts, a condition known as leukopenia.
The proliferation of abnormal cells in the bone marrow can crowd out healthy red blood cell production, resulting in low red blood cell counts and anemia. Leukemia can also suppress platelet production, leading to low platelet counts (thrombocytopenia), which can cause easy bruising and bleeding.
Why Leukemia May Not Appear on a CBC
While a CBC is a valuable screening tool, it is not a definitive diagnostic test for leukemia. In early stages, blood count changes might be minimal or subtle, making detection difficult. Counts might fall within a normal reference range or be attributed to other conditions, such as infections or inflammation.
Some types of leukemia, including chronic or “aleukemic” leukemia, may not release a large number of abnormal cells into the bloodstream. In these instances, cancerous cells might primarily remain in the bone marrow, leading to a CBC that appears relatively normal despite the disease.
Blood counts can fluctuate, and a single CBC might not capture the full picture of what is happening in the bone marrow. Therefore, while a CBC can raise suspicion for leukemia, a normal result does not always rule out the disease, especially in its initial phases.
Confirming a Leukemia Diagnosis
When leukemia is suspected due to abnormal CBC results or concerning symptoms, additional specialized tests are necessary to confirm the diagnosis. A peripheral blood smear involves microscopic examination of a blood sample to identify abnormal cell shapes, sizes, or immature cells (blasts) that may indicate leukemia.
The definitive test for most types of leukemia is a bone marrow biopsy and aspiration. This procedure involves collecting a small sample of bone marrow, typically from the hip bone, for detailed analysis to detect cancerous cells and assess the bone marrow’s health.
Flow cytometry analyzes cells to identify specific markers, helping to classify the exact type of leukemia present. Genetic and molecular testing detects chromosomal abnormalities and gene mutations characteristic of different leukemia subtypes. These comprehensive tests provide the detailed information required for an accurate diagnosis, classification, and to guide treatment decisions.
When to Consult a Doctor
It is important to pay attention to persistent or concerning symptoms, as they can be early indicators of leukemia, even if a recent CBC was normal. Common symptoms include persistent fatigue and weakness, unexplained weight loss, and recurring fevers or night sweats.
Other potential signs are increased susceptibility to infections, easy bruising or bleeding, and tiny red spots on the skin (petechiae). Swollen lymph nodes in the neck, armpits, or groin, as well as an enlarged liver or spleen, can also occur.
If these symptoms are experienced, especially if they are persistent or worsen, consult a healthcare professional. A doctor can evaluate symptoms, consider medical history, and determine if further diagnostic tests are warranted, even if initial blood work appears normal.