Cytochemistry of tartrate-resistant acid phosphatase: 15 years' experience.

Tartrate-resistant acid phosphatase (T-AcP) has been used in the past 15 years as a specific test for the diagnosis of hairy cell leukemia (HCL). However, enzyme activity has been reported to be absent from the hairy cells of rare cases of HCL and to be present in the neoplastic cells of diseases other than HCL. In order to fully utilize T-AcP for the diagnosis of HCL, it is necessary to maximize the sensitivity and specificity of the staining method, to have adequate quality control to ensure technical and interpretative accuracy, and to prepare optimal cytologic and histologic materials for study. In blood, only the presence of cells with intense T-AcP activity is diagnostic of HCL (positive T-AcP test). In tissues other than blood, the presence of cells with intense enzyme activity may not be diagnostic for HCL; assessment of cell morphology and appreciation of the pattern of enzyme localization are also important. In studying the blood of over 1,000 patients, we have found a negative T-AcP test in two of 200 cases of HCL and a positive T-AcP test in three of 800 patients with diseases other than HCL. We believe that the T-AcP test, when performed and interpreted properly, is a useful diagnostic test for HCL.