ABSTRACT
BACKGROUND: Adenosine deaminase (ADA), an enzyme involved in purine metabolism, catalyzes the hydrolytic deamination of adenosine or 2-deoxyadenosine to inosine or 2-deoxyinosine. Human ADA consists of three molecular forms: ADA1, ADA1+CP, and ADA2. The two ADA isoenzymes represent two different gene products and have different tissue distributions, and their concentrations in serum appear to reflect different pathological conditions or physiological responses. Elevation of serum ADA activity has been described especially in leukemia and lymphoma. The purpose of this study was to evaluate the clinical utility of ADA isoenzyme determination in the diagnosis of leukemia. METHODS: We studied the activity of serum ADA and its isoenzyme in 44 leukemic patients. The study population consisted of 17 patients with acute lymphoblastic leukemia (ALL), 23 with acute myeloid leukemia (AML), and 4 with chronic myelogenous leukemia (CML). ADA isoenzyme was measured by erythro-9- (2-hydroxy-3-nonyl) adenine [EHNA] inhibitory assay using the Hitachi 7170 autoanalyzer. RESULTS: The rates of abnormally high total ADA activity were 100% for ALL, 60.8% for AML, and 50% for CML. In isoenzyme pattern, there was a clear difference between ALL and AML. High level of ADA1 activity was found in patients with ALL (P <0.01). The ADA1/ADA2 ratio was significantly higher (P <0.001) in ALL than AML. There was a correlation between ADA1 and absolute number of peripheral blasts in AML (r=0.840). CONCLUSIONS: It is concluded that the measurement of ADA isoenzyme may be a useful biochemical marker for leukemic diagnosis.