This is a medical question of type : exams and tests 
 How to diagnose Hairy Cell Leukemia ? 
 Tests that examine the blood and bone marrow are used to detect (find) and diagnose hairy cell leukemia. The following tests and procedures may be used:         -   Physical exam and history : An exam of the body to check general signs of health, including checking for signs of disease, such as a swollen spleen, lumps, or anything else that seems unusual. A history of the patients health habits and past illnesses and treatments will also be taken.     -   Complete blood count (CBC): A procedure in which a sample of blood is drawn and checked for the following:                - The number of red blood cells, white blood cells, and platelets.      - The amount of hemoglobin (the protein that carries oxygen) in the red blood cells.      - The portion of the sample made up of red blood cells.             -   Peripheral blood smear : A procedure in which a sample of blood is checked for cells that look "hairy," the number and kinds of white blood cells, the number of platelets, and changes in the shape of blood cells.    -   Blood chemistry studies : A procedure in which a blood sample is checked to measure the amounts of certain substances released into the blood by organs and tissues in the body. An unusual (higher or lower than normal) amount of a substance can be a sign of disease.    -   Bone marrow aspiration and biopsy : The removal of bone marrow, blood, and a small piece of bone by inserting a hollow needle into the hipbone or breastbone. A pathologist views the bone marrow, blood, and bone under a microscope to look for signs of cancer.    -   Immunophenotyping : A laboratory test in which the antigens or markers on the surface of a blood or bone marrow cell are checked to see what type of cell it is. This test is done to diagnose the specific type of leukemia by comparing the cancer cells to normal cells of the immune system.    -   Flow cytometry : A laboratory test that measures the number of cells in a sample, the percentage of live cells in a sample, and certain characteristics of cells, such as size, shape, and the presence of tumor markers on the cell surface. The cells are stained with a light-sensitive dye, placed in a fluid, and passed in a stream before a laser or other type of light. The measurements are based on how the light-sensitive dye reacts to the light.    -   Cytogenetic analysis : A laboratory test in which cells in a sample of tissue are viewed under a microscope to look for certain changes in the chromosomes.     -   Gene mutation test: A laboratory test done on a bone marrow or blood sample to check for mutations in the BRAF gene. A BRAF gene mutation is often found in patients with hairy cell leukemia.    -   CT scan (CAT scan): A procedure that makes a series of detailed pictures of areas inside the body, taken from different angles. The pictures are made by a computer linked to an x-ray machine. A dye may be injected into a vein or swallowed to help the organs or tissues show up more clearly. This procedure is also called computed tomography, computerized tomography, or computerized axial tomography. A CT scan of the abdomen may be done to check for swollen lymph nodes or a swollen spleen.