CPT® Code 85540

The CPT® Code 85540 refers to a laboratory test that measures leukocyte alkaline phosphatase (LAP), which is an enzyme found in white blood cells (WBCs), also known as leukocytes. This enzyme plays a role in various physiological processes, and its levels can provide important diagnostic information. Although the use of this test has diminished due to the advent of more advanced diagnostic techniques, it remains relevant in specific clinical scenarios. The LAP test is particularly useful in differentiating chronic granulocytic leukemia from a leukemoid reaction, which is characterized by an elevated white blood cell count that is not due to infection or malignancy. Additionally, this test can aid in the evaluation of patients with conditions such as polycythemia vera, myelofibrosis, aplastic anemia, pernicious anemia, and essential thrombocytopenia. To perform the test, a blood sample is collected through a venipuncture, which is a separately reportable procedure. The whole blood sample is then analyzed under a microscope, utilizing enzyme assays and/or cytochemical stains to assess the levels of leukocyte alkaline phosphatase.