Significance of leukocyte alkaline phosphatase in hairy cell leukemia

Peripheral blood samples of 23 patients who had hairy cell leukemia were examined for leukocyte alkaline phosphatase scores. Leukocyte alkaline phosphatase levels were elevated in seventeen patients (74%), were normal in six (26%), and were not decreased in any patient. The mean leukocyte alkaline phosphatase score was 166 (normal range, 11-95). High leukocyte alkaline phosphatase scores correlated inversely with the absolute number of neutrophils in peripheral blood and were unrelated to other clinical factors, including age and time since splenectomy. High leukocyte alkaline phosphatase scores were also associated with a shift to more immature forms of neutrophil differentiation. These findings are consistent with the view that high leukocyte alkaline phosphatase levels in hairy cell leukemia are secondary to decreased marrow granulocyte reserves and do not necessarily indicate the existence of primary abnormalities of multiple bone marrow cell lines, including the granulocytes, in hairy cell leukemia. The role of the leukocyte alkaline phosphatase assay in the differential diagnosis of hairy cell leukemia with respect to non-Hodgkin's lymphoma, chronic lymphocytic leukemia, and other lymphoid malignancies is discussed.