Diagnosing Hairy Cell Leukemia

Doctors at NYU Langone are experts in diagnosing all types of leukemia, including hairy cell leukemia, a type of blood cancer.

Hairy cell leukemia originates in the bone marrow and affects white blood cells called B lymphocytes. Abnormal B lymphocytes, along with other blood cells, leave the bone marrow and circulate in the bloodstream and the spleen, an organ that is part of the immune system and that filters the blood. Because hairy cell leukemia is slow growing, some people may never experience any symptoms.

In people with hairy cell leukemia, the bone marrow produces abnormal B lymphocytes. These cells have tiny hair-like projections, giving the cancer its name. Abnormal B lymphocytes, along with other blood cells, leave the bone marrow and circulate in the bloodstream and the spleen, an organ that is part of the immune system and that filters the blood.

Because hairy cell leukemia is slow growing, some people may never experience any symptoms.

In others, as abnormal B lymphocytes, or leukemia cells, collect in the spleen, the organ enlarges, causing the abdomen to swell. The spleen may also trap normal blood cells, resulting in lowered numbers of red cells and platelets in the bloodstream. The enlarged spleen can press on the stomach, causing you to feel unusually full. Leukemia cells also sometimes collect in the liver, another organ that filters the blood, causing it to swell.

Abnormal B lymphocytes can also multiply and collect in the bone marrow and blood, crowding out and reducing the number of healthy blood cells.

Low levels of red blood cells, which normally carry oxygen to the body’s organs and tissues, can lead to anemia, a condition that causes fatigue, weakness, and shortness of breath. Low levels of healthy white blood cells increase the risk of infection and can cause fever, chills, or sweating. In addition, low levels of platelets, blood cells that stop bleeding, can interfere with blood clotting; people with hairy cell leukemia may notice more frequent nosebleeds or excessive bleeding if they cut themselves.

Although this is rare, B lymphocytes can collect in the body’s lymph nodes, causing them to enlarge. Lymph nodes are small immune system glands that trap viruses and bacteria. You may first notice swollen lymph nodes in your neck, armpits, or groin.

Hairy cell leukemia is a chronic condition, meaning it may never go away. However, NYU Langone hematologists—doctors who study and treat diseases of the blood—can usually treat this form of cancer so that it goes into remission, meaning the signs and symptoms of the condition subside or disappear.

The causes of hairy cell leukemia are not fully understood. But researchers recently found that a mutation in a gene called BRAF is present in nearly all people with the condition. Healthy versions of this gene help cells grow, divide, and eventually self-destruct, which is normal. When the BRAF gene mutates, cells may grow uncontrollably and become cancerous.

NYU Langone doctors conduct a physical exam to check for signs of the disease, such as shortness of breath or swelling of the abdomen, and ask about your medical history. They may also order several tests to diagnose hairy cell leukemia.

Blood Tests

Doctors use blood tests to check for low levels of red and white blood cells and platelets, which are telltale signs of hairy cell leukemia. They can also find out whether your blood contains hairy cell leukemia cells—the abnormal B lymphocytes with characteristic hairlike projections. Doctors determine how many of these cells are present. High levels of abnormal B lymphocytes indicate that the cancer is more advanced.

Hematopathologists, doctors who study diseases of the blood, may stain blood cells with a special dye and examine them under a microscope with a laser light to evaluate their size and shape. They may also stain lymphocytes with specific antibodies that recognize certain immune system proteins, called cell surface markers, typically found on hairy cell lymphocytes.

The antibody–cell mixture is then studied for the presence or absence of these cell surface proteins. Determining the presence or absence of these proteins distinguishes what kind of leukemia is present and leads to proper treatment.

If these analyses are inconclusive, doctors can test for BRAF gene mutations to help diagnose hairy cell leukemia.

Bone Marrow Biopsy

Because abnormal B lymphocytes develop in the bone marrow, your doctor may perform a bone marrow biopsy to confirm a diagnosis.

In this procedure, your doctor administers a local anesthetic and removes a tiny sample of bone and marrow from the back of the pelvis. The sample is evaluated under a microscope for signs of cancer and tested for mutations that indicate the presence of hairy cell leukemia.

CT Scans

If a doctor notices that your spleen or liver is enlarged during a physical exam, he or she may order a CT scan. This scan uses X-rays and a computer to create three-dimensional, cross-sectional images of the body. To enhance the images, your doctor may give you a contrast agent, a type of dye either injected into a vein or taken by mouth that highlights any abnormalities. A CT scan may also detect swollen lymph nodes.


A doctor may order an ultrasound, which uses sound waves to create detailed images of the spleen or liver. Because it doesn’t use radiation, doctors may prefer ultrasound to other tests if multiple scans are needed to monitor whether organs are enlarged as a result of abnormal B lymphocytes. Ultrasound may also detect swollen lymph nodes.

Next Steps

After our doctors have completed their testing, they can determine what type of medical care is needed. Sometimes, people who have hairy cell leukemia without any symptoms do best without treatment, an approach called watchful waiting, in which doctors monitor the condition without immediately treating it.

Hairy cell leukemia that is causing symptoms usually is treated with medications or, if the spleen becomes too large and is in danger of rupturing, with surgery.

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