A complete blood count (CBC) is a common blood test. When leukemia, a cancer of the blood and bone marrow, is present, a CBC can reveal important clues. While this test provides indications of potential issues, it is not a standalone diagnostic tool for leukemia. Instead, abnormal CBC results often serve as a screening mechanism, prompting the need for further, more specialized investigations.
Understanding the Complete Blood Count
A complete blood count measures several components of the blood. The test quantifies and assesses red blood cells (RBCs), white blood cells (WBCs), and platelets. It also measures hemoglobin, the protein in red blood cells that carries oxygen, and hematocrit, the percentage of blood volume made up of red blood cells.
White blood cells (leukocytes) are part of the immune system, fighting infections. There are five main types: neutrophils, lymphocytes, monocytes, eosinophils, and basophils, each with specific roles. Red blood cells (erythrocytes) transport oxygen from the lungs to tissues and carry carbon dioxide back to the lungs.
Platelets (thrombocytes) are cell fragments that stop bleeding by forming clots at damaged blood vessels. These blood components are continuously produced in the bone marrow, a spongy material inside bones. The CBC provides a snapshot of these cells, indicating if their numbers or characteristics fall outside typical ranges.
How Leukemia Impacts CBC Results
Leukemia affects blood cell production in the bone marrow, leading to specific abnormalities detectable on a CBC. One noticeable change often involves white blood cells. Leukemia generally causes an overproduction of immature white blood cells that do not function properly.
In some cases, especially with acute leukemia, the white blood cell count can be extremely high, sometimes reaching 100,000 to 400,000 cells per microliter, significantly above the normal range of 4,000 to 11,000. The presence of immature or abnormal white blood cells, known as blasts, is a significant indicator of leukemia. These cancerous cells can crowd out healthy blood-forming cells in the bone marrow, hindering the production of normal white blood cells, red blood cells, and platelets.
This crowding can lead to a paradoxically low white blood cell count in some types of leukemia, as immature cells may get trapped in the bone marrow and not circulate. Leukemia also frequently results in abnormalities in red blood cell counts, leading to anemia. This reduction in healthy red blood cells can cause symptoms such as fatigue, weakness, and pale skin. The CBC would show low red blood cell counts, as well as reduced hemoglobin and hematocrit levels.
Platelet counts are also commonly affected, often resulting in abnormally low numbers. The crowding out of healthy cells suppresses platelet production, leading to thrombocytopenia. A low platelet count can lead to symptoms such as easy bruising, frequent nosebleeds, and tiny red spots on the skin called petechiae. These changes serve as warning signs for further medical investigation.
The Need for Further Diagnostic Tests
Abnormalities seen in a CBC, such as unusual cell counts or the presence of blasts, indicate the need for more specialized diagnostic procedures. These tests are important for confirming leukemia, identifying its specific type, and guiding treatment strategies.
One primary follow-up test is a bone marrow biopsy and aspiration. This procedure involves collecting a small sample of bone marrow to examine the cells directly. Pathologists analyze the marrow for abnormal cells, assess cellularity, and confirm the presence and type of leukemia. This direct examination provides important information that a peripheral blood sample cannot.
Flow cytometry is another advanced diagnostic tool used to analyze the surface markers of cells. This technique helps identify specific types of leukemia cells by recognizing unique proteins on their surfaces. It can accurately classify the lineage and maturity of abnormal cells, which is important for determining the exact subtype of leukemia.
Genetic and chromosomal analyses, including cytogenetics and Fluorescence In Situ Hybridization (FISH), are also performed. These tests look for specific genetic mutations or chromosomal abnormalities within the leukemic cells. Identifying these genetic changes helps classify the leukemia subtype, predict its behavior, and inform targeted treatment approaches. Together, these comprehensive tests provide the detailed information necessary for an accurate diagnosis and personalized treatment plan.