What is indicated by an elevated LAP score in a patient?

An elevated leukocyte alkaline phosphatase (LAP) score is indicative of a reactive process, particularly in cases of a leukemoid reaction. This reaction is characterized by a significant increase in white blood cell count, typically in response to an infection, inflammation, or other stressors in the body. In this context, the LAP score rises because alkaline phosphatase is an enzyme associated with mature neutrophils, which are elevated during such reactions.

Leukemoid reactions can present similarly to leukemias but generally reflect a physiological response rather than a malignancy. Patients commonly have a high count of mature neutrophils, and the elevated LAP score serves as a marker of the functional activity of these neutrophils, confirming that the increase is a response to stress rather than a neoplastic process.

In contrast, conditions such as chronic myelogenous leukemia typically lead to a low LAP score due to the presence of immature cells like myeloblasts that lack high alkaline phosphatase activity. Other conditions, like polycythemia vera and acute leukemia, also do not correlate with an elevated LAP score. Hence, the elevated LAP score specifically aligns with leukemoid reactions, distinguishing it from other hematological disorders.