Osmotic Fragility Test

Laboratory testing is a very essential part of the clinical decision making process. The test result strongly influence medical diagnosis as well as the therapy applied (Lippi, 2006).Hematological results are often influenced by number of pre-analytical variables,these include the anticoagulants used, methods of analysis, the storage temperature and the time between when the samples were taken and when they were analyzed (Gulatietal., 2002).Delayed sample analysis could result in hematological changes in the measured parameter, which could complicate the interpretation of the resulting data (Lippi et al., 2005).

Whole blood is usually treated with anticoagulants to prevent them from clotting. Ethylenediamine tetraacetic acid (EDTA)salt sodium

The information obtained may furnish the diagnosis of many diseases, serve as guide to therapy and as an indicator of harmful effect of radiotherapy and chemotherapy (Tatsumi etal , 2002 )

The sooner hemolysis occurs , the greater the osmotic fragility of the cells ( Parpart etal. , 1947 ). The tests are based on the measure of red blood cell lysis as a function of osmotic stress. When erythrocytes are placed in hypotonic solutions, they begin to take on water osmotically. This results in swelling of the cell until the critical volume is reached, afterward the membrane at first leaks and then bursts releasing hemoglobin (Faulkner and king 1970 ).

The osmotic fragility test can be performed on freshly taken red cells. The susceptibility to osmotic lysis is primarily determined by the surface area to volume ratio of erythrocytes .Increased osmotic fragility typically occurs in hereditary spherocytosis. Because of their reduced surface membrane area in respect to the cell volume, spherocytes take up less water in a hypotonic solution before rupturing than do normal blood cells. They cannot expand as much as normal discoid erythrocytes and are osmotically more fragile ( Roper and Layton, 2012