Leukemia is a group of cancers that begins in the blood-forming tissues, most often in the bone marrow. It involves the rapid production of abnormal blood cells that can crowd out healthy blood cells. While blood tests are frequently the first step in diagnosing leukemia, they are not always diagnostic. This article explores why initial blood tests might not always detect leukemia and outlines further diagnostic steps.
Understanding Blood Tests for Leukemia
Routine blood tests, primarily a Complete Blood Count (CBC), are often the initial assessment for suspected leukemia. A CBC measures red blood cells, white blood cells, and platelets. Abnormalities in these counts, such as unusually high or low white blood cell counts, low red blood cell counts (anemia), or low platelet counts, can signal an issue with blood cell production. For instance, a high white blood cell count, especially with immature cells, can indicate some types of leukemia.
A peripheral blood smear is also performed. This involves examining a drop of blood under a microscope to visualize the appearance, size, and shape of blood cells. A pathologist can identify immature cells, known as blasts, or other abnormal cell shapes indicative of leukemia, even if overall cell counts are not dramatically altered. This examination provides more detailed information than the automated CBC alone.
When Blood Tests May Not Detect Leukemia
Blood tests can sometimes miss leukemia, especially in its early stages. In its nascent phase, the number of abnormal cells circulating in the blood might be too low for detection by standard tests. The disease may primarily reside within the bone marrow, with subtle or no signs in the bloodstream.
Another scenario is “aleukemic leukemia,” a rare form where leukemic cells are present in the bone marrow but their number in the peripheral blood is relatively low or even normal. In such cases, a blood test might show normal or decreased white blood cell counts, despite cancerous cells in the bone marrow. Some rare leukemia subtypes may not show typical blood count abnormalities. Other conditions or normal blood cell fluctuations can also mask or mimic leukemia signs, potentially delaying diagnosis.
Beyond Blood Tests: Comprehensive Diagnosis
If blood tests suggest leukemia, or if symptoms persist despite normal initial results, further diagnostic procedures are necessary to confirm the diagnosis and classify the specific type. A bone marrow biopsy and aspiration is the primary method for confirming leukemia. During this procedure, a small bone marrow sample, often from the hip, is removed and examined to assess blood-forming cells for cancerous changes and determine the percentage of abnormal cells.
Specialized laboratory tests are performed on blood or bone marrow samples. Flow cytometry identifies specific cell markers, helping differentiate between healthy and cancerous cells and classify the exact subtype. Cytogenetic and molecular genetic testing examine chromosomes and genes for abnormalities or mutations. Identifying these genetic changes is important for precise classification and guiding treatment, as different subtypes respond to different therapies. Imaging tests (X-rays, CT scans, MRIs) are not for primary diagnosis but can check for spread to other organs or identify complications like enlarged lymph nodes or spleen.
Recognizing Symptoms and Seeking Further Evaluation
Even if initial blood tests do not indicate leukemia, recognizing persistent symptoms is important for seeking further medical evaluation. Leukemia symptoms can be vague and non-specific, often resembling other common illnesses.
Common symptoms include:
- Unexplained fatigue or weakness
- Frequent or severe infections
- Easy bruising or bleeding
- Recurrent nosebleeds
- Tiny red spots on the skin (petechiae)
- Fever
- Night sweats
- Unexplained weight loss
- Bone pain
- Swelling in the lymph nodes, liver, or spleen
If symptoms are persistent, worsening, or unusual, discuss them with a healthcare provider. A doctor’s clinical judgment, combined with a patient’s symptoms and medical history, guides the diagnostic process. Advocating for thorough investigation based on sustained symptoms helps ensure an accurate and timely diagnosis.