The diagnostic significance of a prolonged erythrocytic glycerol lysis time (GLT50).

The predictive value of a prolonged glycerol lysis time (GLT50) was assessed by analysis of case records of 100 consecutive subjects with values greater than 73 seconds (normal = 26--73 seconds) reported by the clinical laboratory of The New York Hospital. There were 72 cases of hemoglobinopathy: 65 thalassemia trait, four sickle-thalassemia, and one each of Hb D-thalassemia, sickle-C disease, and sickle-cell anemia. Nine of the remaining subjects had iron-deficiency anemia, three had chronic renal disease, and seven had miscellaneous disorders. Four subjects were apparently normal, and in five cases there was insufficient information for a diagnosis. Of 78 patients who had both a prolonged GLT50 and microcytosis, 67 (86%) had thalassemia trait and seven (9%) had iron-deficiency anemia. In 74 patients with GLT50 greater than 100 seconds, thalassemia trait was found 16 times as often as uncomplicated iron-deficiency anemia. All 31 subjects with GLT50 greater than 180 seconds had hemoglobinopahy. A prolonged GLT50 strongly suggests thalassemia trait, especially when greater than 100 seconds or associated with microcytosis.