Learn About Leukemia Testing Options and Procedures

Understanding Leukemia and Why Testing Matters

Leukemia is a cancer that starts in blood-forming cells, usually in the bone marrow. Unlike solid tumors, leukemia cells circulate through the bloodstream and can affect multiple organs. The disease comes in several types based on how fast it grows and what type of blood cell it involves. Acute leukemias develop quickly over days or weeks, while chronic leukemias develop slowly over months or years. Common types include acute lymphoblastic leukemia (ALL), acute myeloid leukemia (AML), chronic lymphocytic leukemia (CLL), and chronic myeloid leukemia (CML).

Testing plays a crucial role in leukemia diagnosis and treatment planning. When a person shows symptoms like unexplained bruising, bleeding, fatigue, recurring infections, or bone pain, doctors use various tests to determine whether leukemia is present. Testing also helps doctors identify which specific type of leukemia someone has, which directly affects treatment decisions. Additionally, tests monitor how well treatment is working and watch for signs of cancer returning after treatment ends. According to the American Cancer Society, about 60,650 new cases of leukemia were expected to be diagnosed in 2023, making accurate testing essential for the large number of people affected.

Different tests provide different information. Some tests look at the overall number and appearance of blood cells. Others examine the genetic makeup of cells to identify specific mutations that determine prognosis and guide treatment selection. Some tests check whether leukemia cells have spread to the brain or spinal fluid. Understanding what each test does helps patients and families work with their medical team and know what to expect during the diagnostic process.

Practical Takeaway: Leukemia testing involves multiple procedures because each test provides different information about the disease. Knowing why your doctor is recommending specific tests helps you understand your diagnosis more clearly.

Complete Blood Count (CBC) and Blood Smear Tests

The Complete Blood Count, or CBC, is usually the first test performed when leukemia is suspected. This test measures the number of different types of blood cells in your blood: white blood cells, red blood cells, and platelets. In leukemia, the bone marrow produces too many immature white blood cells called blasts, which crowds out healthy cells. A CBC shows if these numbers are abnormal. The test also measures hemoglobin (the protein that carries oxygen) and hematocrit (the percentage of red blood cells), both often low in leukemia patients.

The results come back with specific numbers. For example, a normal white blood cell count ranges from 4,000 to 11,000 cells per microliter of blood. In acute leukemia, this count can jump to 100,000 or higher, though some leukemia patients have normal or low counts. The CBC is a quick test—blood is drawn from a vein and analyzed by a machine within hours. No special preparation is needed, though some doctors prefer patients fast beforehand, which means not eating for 8 to 12 hours before the test.

A peripheral blood smear is performed alongside the CBC. A small drop of blood is spread on a glass slide, stained, and examined under a microscope. This allows a specialist called a hematopathologist to look at the actual appearance and shape of blood cells. In leukemia, blast cells look different from normal cells—they are larger and have more cytoplasm. The smear can reveal immature cells, abnormal shapes, or other clues suggesting leukemia. Sometimes the smear alone suggests leukemia, but it cannot confirm the diagnosis on its own.

Practical Takeaway: CBC and blood smear tests are non-invasive screening tools that usually trigger further testing if abnormal results appear. These tests take little time and require only a standard blood draw.

Bone Marrow Biopsy and Aspiration Procedures

When initial blood tests suggest leukemia, doctors perform a bone marrow biopsy and aspiration to confirm the diagnosis. This procedure is more involved than a blood draw but provides critical information. During the procedure, a doctor inserts a needle into the hip bone (iliac crest) to remove a small sample of bone marrow—the soft tissue inside bones where blood cells are made. Most doctors use local anesthesia to numb the skin and area around the bone, though patients may feel pressure and brief discomfort when the needle enters the bone.

The aspiration removes liquid marrow through a thin needle, while the biopsy removes a small solid core of bone and marrow tissue. Both samples go to a laboratory where specialists examine the cells under a microscope and perform additional testing. The bone marrow contains many more immature cells than peripheral blood, making it easier to see abnormalities. In leukemia, the marrow is often packed with blast cells, sometimes comprising 80% or more of all cells, compared to a normal level of less than 5%.

The procedure typically takes 15 to 30 minutes. Patients sit or lie on their side while the doctor cleans the skin with antiseptic and injects local anesthesia. Some patients receive sedation to reduce anxiety, though this is not required. After the procedure, patients may feel soreness at the needle site for a few days and should avoid strenuous activity for 24 hours. Serious complications like infection or excessive bleeding are rare, occurring in less than 1% of procedures. Results usually come back within a few days to a week, depending on what additional testing the laboratory needs to perform.

Practical Takeaway: A bone marrow biopsy is essential for confirming leukemia diagnosis. Although it causes brief discomfort, it provides the detailed cell information doctors need to determine the specific type of leukemia and plan treatment.

Cytochemical Stains and Immunophenotyping Tests

Once bone marrow or blood samples are collected, laboratory tests identify exactly what type of leukemia is present. Cytochemical stains are chemical reactions applied to cells on microscope slides that reveal specific markers. Different types of leukemia react differently to these stains, helping narrow down the diagnosis. For example, myeloperoxidase (MPO) staining is positive in AML but negative in ALL, helping distinguish between these two acute leukemias. These stains have been used for decades and remain part of standard testing protocols.

Immunophenotyping is a more advanced test that uses special antibodies to identify protein markers on the surface of leukemia cells. A technique called flow cytometry applies fluorescent-labeled antibodies to the cells and then passes them through a laser. Each cell produces a distinctive light pattern based on which proteins it has. This test can identify dozens of different markers and classify cells with precision. Immunophenotyping distinguishes between lymphoblastic and myeloid leukemias and can identify subtypes within each category. Results typically show a percentage breakdown of cells and their characteristics.

These tests take several days to a week to complete because they require specialized equipment and training. The information they provide is crucial for treatment planning. Different types of leukemia respond to different chemotherapy drugs and protocols. For instance, patients with ALL containing a specific genetic marker called the Philadelphia chromosome may benefit from targeted therapies like tyrosine kinase inhibitors. Without immunophenotyping and genetic testing, doctors would not know which treatments would be most effective for each patient.

Practical Takeaway: Immunophenotyping and cytochemical stains pinpoint the specific subtype of leukemia, which directly determines which medications and treatment approaches doctors will recommend.

Cytogenetics and Molecular Genetic Testing

Cytogenetics examines the chromosomes inside leukemia cells to identify structural abnormalities. In a normal person, cells contain 23 pairs of chromosomes. In leukemia, chromosomes may be missing, duplicated, or rearranged. Some of these changes are very common in specific leukemia types. For example, the Philadelphia chromosome—a rearrangement between chromosomes 9 and 22—occurs in nearly all cases of chronic myeloid leukemia and in about 20% of adult acute lymphoblastic leukemia cases. Detecting this abnormality changes treatment recommendations significantly.

Cytogenetics uses a technique called FISH (fluorescence in situ hybridization) where fluorescently labeled probes attach to specific chromosomes or genes. Under a microscope, these probes glow, revealing abnormalities. Another approach