RBC osmotic fragility test, which mixes RBCs with varying concentrations of saline RBC autohemolysis test, which measures the amount of spontaneous hemolysis occurring after 48 hours of sterile incubation Direct antiglobulin (direct Coombs) test, to rule out spherocytosis due to autoimmune hemolytic anemia RBC fragility is characteristically increased, but in mild cases of either hereditary spherocytosis or hereditary elliptocytosis, it may be normal unless sterile defibrinated blood is first incubated at 37 ° C for 24 hours to deplete red cell ATP (adenosine triphosphate) stores.