Diagnostic value of the glycerol lysis test

The diagnostic value of the standard glycerol lysis test (GLT) has been evaluated by studying 95 cases of hereditary spherocytosis (HS), 513 beta- and 25 alpha-thalassemia trait (Th) carriers, 170 iron-deficient patients (ID), and 217 patients with miscellaneous hematological conditions. The sensitivity of the test, at 95% specificity, was 97% for beta-Th, 53% for ID, and only 36% for HS, so that the predictive value of a positive result is practically nil for HS, 50% to 85% for Th, and 10% to 35% for ID, depending on the prevalence ratio of the disease in the examined population. The technical variability of GLT, explored by a proper experimental design, was found to be rather high, its main components being repeatability and variability of reagent preparations. The dependence of the results on operators was negligible. It is concluded that GLT is not suitable as a laboratory test for the detection of abnormalities in red cell osmotic fragility because of its very low sensitivity toward increased fragility. For decreased red cell osmotic fragility, the sensitivity of GLT is high; however, it is less valuable than the traditional 0.35% NaCl method as mass screening test for the detection of beta-Th, giving more false positive results.