Usefulness of cryohemolysis test in the diagnosis of hereditary spherocytosis

The clinical suspicion of hereditary spherocytosis (HS) must be confirmed at the clinical laboratory. The osmotic fragility test (OFT) and the autohemolysis test(AHT) are the worldwide accepted assays to establish a definite diagnosis of HS; however, they have some disadvantages. We describe herein our experience with the cryohemolysis test (CHT) as a tool to confirm the HS diagnosis. We included four groups of subjects, namely, patients with clinical HS, patients with mechanical heart valve prosthesis, malignant hematological diseases and healthy blood donors. CHT was carried out in all the groups, while OFT and AHT only in the HS patients and healthy individuals. OFT and AHT were performed according to previously described techniques. CHT was performed using red blood cells incubated in a hypertonic solution, preheated for 10 min and then transferred to an ice bath for an additional 10 min. The resulting cryohemolysis was determined measuring the free hemoglobin in the sample. There were no differences among the groups in terms of general characteristics. All HS suspicious patients had a positive OFT and AHT. CHT was positive in all patients from the HS group but in none of the subjects from the control groups (p < 0.001). We found that CHT is a faster and easier-to-perform assay compared with OFT and AHT. Moreover, using CBT, the zone between normal and abnormal results is wider than OFT or AHT. We propose 0.7 to 11% hemolysis as reference values for CHT.