
A leukocyte alkaline phosphatase (LAP) test is a laboratory test that can be conducted on a sample of your blood. Your doctor can order it to measure the amount of alkaline phosphatase, a group of enzymes, in certain white blood cells. Before the advent of more advanced tests, the LAP test was commonly use to diagnose chronic myeloid leukemia (CML). This is a type of cancer than affects white blood cells. If you have CML, the level of alkaline phosphatase in your white blood cells will be lower than normal. Some doctors still order the LAP test to check for signs of CML. It can also help them rule out other disorders. But it’s now generally accepted that a cytogenetic test (a test of your cells and chromosomes) is needed to confirm a CML diagnosis. As a result, the LAP test is used less often now than in the past.