Doctors use many blood and bone marrow tests to diagnose leukemia and to find out the extent to which it may have spread. Although a patient’s signs and symptoms may cause a doctor to suspect leukemia, it is diagnosed only by blood and bone marrow tests. Some tests may also determine which treatments may be the most effective. Your doctor may consider these factors when choosing a diagnostic test:

• Age and medical condition
• Type of cancer suspected
• Severity of symptoms
• Previous test results

The following tests may be used to diagnose PLL and HCL:

Blood tests [2]. The diagnosis of PLL or HCL begins with a blood test, called a complete blood count (CBC), that measures the numbers of different types of cells in a person's blood. If the blood contains many white blood cells, B-cell leukemia may be suspected. However, patients with HCL often have a very low level of white blood cells.

Bone marrow biopsy and aspiration [3]. These two procedures are similar and often done at the same time. Bone marrow has both a solid and a liquid part. A bone marrow biopsy is the removal of a small amount of solid tissue using a needle. An aspiration removes a sample of fluid with a needle. The sample(s) are then analyzed by a pathologist (a doctor who specializes in interpreting laboratory tests and evaluating cells, tissues, and organs to diagnose disease) to determine the number and type of abnormal cells. A common site for the bone marrow biopsy and aspiration is the pelvic bone, which is located in the lower back by the hip. The skin in that area is usually numbed with medication beforehand, and other types of anesthesia (medication to block the awareness of pain) may be used.

Molecular testing. Your doctor may recommend running laboratory tests on the leukemia cells to identify specific genes, proteins, and other factors unique to the leukemia. Immunophenotyping is the examination of antigens, a specific type of protein, on the surface of the leukemia cells. Immunophenotyping allows the doctor to confirm the exact type of leukemia. Cytogenetics is the examination of the leukemia cells for chromosome (long strands of genes) abnormalities. It helps the doctor confirm the diagnosis and may help to determine the person’s prognosis (chance of recovery). Results of these tests will also help decide whether your treatment options include a type of treatment called targeted therapy (see Treatment [4]).

Computed tomography (CT or CAT) scan [5]. A CT scan creates a three-dimensional picture of the inside of the body with an x-ray machine. A computer then combines these images into a detailed, cross-sectional view that shows any abnormalities or tumors. Sometimes, a contrast medium (a special dye) is injected into a patient’s vein to provide better detail. A CT scan also shows enlarged lymph nodes or a swollen spleen.

Find more about what to expect when having common tests, procedures, and scans [6].

After these diagnostic tests are done, your doctor will review all of the results with you. If the diagnosis is leukemia, these results also help the doctor describe the cancer. Learn more about the first steps to take after a diagnosis of cancer [7].