A Modification of the ‘Pink Test’ May Improve the Diagnosis of Hereditary Spherocytosis

Prof. L. Pinto, Department of Pediatrics, University of Naples, Via San Andrea delle Dame 4, 1-80138 Napoli (Italy) Several tests for the laboratory diagnosis of hereditary spherocytosis (HS) have been proposed as screening tests for the detection of spherocytes in the peripheral blood, but at present none of them is a single and unequivocal test for HS. In 1984 Vettore et al. [1] proposed a quantitative determination of hemo-lysis of small blood samples in a solution containing glycerol at pH 6.66, called ‘pink test’. This test showed a high diagnostic sensitivity (100%) whereas the specificity was 97 %. Judkiewicz et al. [2] proposed a modification requiring only 10 μl of blood taken by fing-erprick without anticoagulant, thus eliminating the necessity of venipuncture. In their report the threshold value of hemolysis for suspecting HS was still lower (18 versus 28.5 %) and there was no overlap between HS and control subjects (100% of specificity and sensitivity). We have carried out an investigation aimed to evaluate the reproducibility of the ‘pink test’ and the effect of storage time of the sample on its results. We examined 50 healthy subjects and 15 patients affected with HS, whose diagnosis was established on the basis of red cell morphology, osmotic fragility, autohemo-lysis, clinical signs, blood values and family studies. We performed the ‘pink test’ with the hemolyzing medium according to Vettore et al. [1], at pH 6.66 and Table 1. Percent hemolysis of blood from healthy controls and HS patients in the original version of the ‘pink test’ and in the proposed modification after 24 h of incubation (24 °C)