Diagnosis of the hemolytic state using serum levels of erythrocyte adenylate kinase

Red cell hemolysis is classically diagnosed by a combination of nonspecific laboratory tests, including serum bilirubin, LDH, and the reticulocyte count. None of these tests alone or in combination has the specificity to reliably ascertain the presence of hemolysis. We have previously demonstrated that erythrocyte adenylate kinase (EAK) is a red cell specific enzyme released from damaged red cells. Its activity can be measured in serum by rapid electrophoresis or immunological methods and correlates linearly with the degree of hemolysis in vitro. We now report on a clinical study comparing EAK levels in patients with and without hemolysis. The clinical diagnosis of hemolysis was established in hospitalized patients with anemia by the combined elevation of the bilirubin, LDH, and reticulocyte count in the absence of liver disease and demonstrable blood loss. The normal range of serum EAK was determined in 30 healthy nonanemic voluntary blood donors and was 0-3.5 Units (mean = 0.5). In 25 patients with hemolytic anemia due to sickle cell disease, hemolytic transfusion reactions, or TTP, the mean EAK level was 62.4 with a range 0-298 Units (P < 0.001 compared to normals). Levels of EAK exceeded the normal range in 24 of 25 patients (96%). In a control group of 44 hospitalized patients with liver disease or myocardial infarction and no clinical evidence of hemolysis, the mean EAK level was 0.12 with a range of 0-3.2 (P = 0.1, NS compared to normals and P < 0.001 compared to patients with hemolysis). None of the control patients had EAK levels that exceeded the normal range. The diagnostic sensitivity of the EAK assay for hemolysis, as calculated according to Baye's algorithm, was 96%, with a specificity and accuracy of 97%. Measurement of serum EAK represents a highly sensitive and specific test for the diagnosis of hemolytic anemia. (C) 2000 Wiley-Liss, Inc.