Differential Diagnosis for Leukemoid Reaction vs. Leukemia

The leukocyte alkaline phosphatase (LAP) stain is a useful diagnostic tool to differentiate between a leukemoid reaction and certain types of leukemia. Here's a categorized differential diagnosis:

• Single most likely diagnosis:
  • A. Chronic myelocytic leukemia (CML): CML typically has low LAP scores, whereas a leukemoid reaction usually has high LAP scores. This distinction makes CML the most likely diagnosis to be differentiated from a leukemoid reaction using the LAP stain.
• Other Likely diagnoses:
  • D. Acute myelocytic leukemia (AML): While AML can sometimes present with variable LAP scores, it is less commonly distinguished from a leukemoid reaction by LAP stain alone compared to CML. However, it remains a consideration in the differential diagnosis due to its potential to mimic a leukemoid reaction in clinical presentation.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.):
  • None specifically fit this category in the context of LAP stain differentiation, as the primary use of LAP is to distinguish between CML and a leukemoid reaction. However, all forms of leukemia should be considered in a broad differential diagnosis for any patient presenting with signs of a leukemoid reaction, due to the critical importance of early diagnosis and treatment of leukemia.
• Rare diagnoses:
  • B. Chronic lymphocytic leukemia (CLL) and C. Polycythemia vera: These conditions are less likely to be directly differentiated from a leukemoid reaction using the LAP stain. CLL is a lymphoproliferative disorder and would not typically be confused with a myeloid leukemoid reaction based on LAP scores. Polycythemia vera is a myeloproliferative neoplasm that can cause an increase in white blood cells but is diagnosed based on other specific criteria, including an increase in red blood cells and often, an increase in platelets.