WHITE BLOOD CELL ENZYMES

WBCs in peripheral blood samples retain enzymatic
activity and can alter substrates added in the laboratory. The presence of enzymatic activity is useful in
studying cells that are so morphologically abnormal
on stained smear that it is difficult to determine their
cell line of origin (see Fig. 1–2). The two most
common WBC enzyme tests are the test for leuko-
cyte alkaline phosphatase, an enzyme found in
neutrophils, and the periodic acid–Schiff stain,
which tests for enzymes found in granulocytes and
erythrocytes. Both tests are used to diagnose hema-
tologic disorders, especially leukemias. Specific
causes of alterations in WBC enzymes are presented
in Table 1–12. Another WBC enzyme test, tartrate-
resistant acid phosphatase (TRAP), is performed to
diagnose hairy cell leukemia, because this enzyme
activity is present in the lymphocytic cells of this
type of leukemia. Additional details for each test are
briefly discussed subsequently.