Osmotic Fragility, Erythrocytes
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Spherocytes are osmotically fragile cells that rupture more easily in a hypotonic solution than do normal RBCs. Because they have a low surface area:volume ratio, they lyse at a higher osmolarity than do normal discocyte (RBCs). Cells that have a larger surface area:volume ratio, such as target cells or hypochromic cells are more resistant to lysing. After incubation, an increase in hemolysis is seen in spherocytes. Hereditary spherocytosis typically has greater number of spherocytes than other causes of spherocytosis. Therefore, the degree of lysis is usually more pronounced, but this is not always the case. Some rare disorders can also cause marked fragility and hereditary spherocytosis cases can display moderate fragility.
Confirming or detecting mild spherocytosis
An interpretive report will be provided.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Spherocytosis of any cause will result in increased osmotic fragility. Infrequently, other congenital hemolytic disorders may also be associated with positive results, as in patients with congenital nonspherocytic hemolytic anemia due to RBC enzyme deficiencies.
Patients with an immunohemolytic anemia, or who have recently received a blood transfusion may also have increased RBC lysis.
The shipping control specimen is required to adequately interpret these cases, as temperature extremes can increase the fragility of the specimen and cause false-positive results.
Osmotic fragility results will be reported if the shipping control is normal.
If the shipping control is abnormal and the osmotic fragility results on the patient are within normal range, the results will be reported; however, a comment will be added to the report indicating that the shipping control was not entirely satisfactory.
The test will be cancelled if the patient specimen and shipping control are both abnormal.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
> or =12 months:
0.50 g/dL NaCl (unincubated): 3-53% hemolysis
0.60 g/dL NaCl (incubated): 14-74% hemolysis
0.65 g/dL NaCl (incubated): 4-40% hemolysis
0.75 g/dL NaCl (incubated): 1-11% hemolysis
Reference values have not been established for patients who are <12 months of age.
Clinical References Provides recommendations for further in-depth reading of a clinical nature
Palek J, Jarolin P: Hereditary spherocytosis. In Hematology. Fourth edition. Edited by WJ Williams, E Beutler, AJ Erslev, MA Lichtman. New York, McGraw-Hill Book Company, 1990, pp 558-569