The diagnosis of leukopenia can be done with a simple blood draw. This blood test is called a complete blood count (CBC) and measures the number of white blood cells. This test determines the amount of white blood cells in the bloodstream; depending on the number of white blood cells, the severity of the problem is determined.
Another technique is flow cytometry (to rule Leukemia ). In this technique, cells and chromosomes are counted and examined for their suspension in a fluid stream, and passing through an electronic detection apparatus.
If not diagnosed by the CBC, you can perform a bone marrow biopsy.