Supernatant hemoglobin determinations after prolonged blood storage.

Measurement of extracellular hemoglobin is useful for assessing the relative success of different blood storage strategies. The test is now also included in routine quality assurance procedures. With the recent trend towards transfusion of concentrated red cells resuspended in "additive" solutions, a safe and efficient method for the estimation of hemoglobin in these units is required. We have developed a method suitable for this purpose, based on the formation of cyanomethemoglobin. Tetramethylbenzidine (TMB) methods were also investigated and shown to detect hemoglobin and hemoglobin derivatives quantitatively when present in packed cell supernatants. A close correlation was recorded between the estimates of supernatant hemoglobin using the 2 techniques with 68 stored red cell concentrates. Because of its simplicity, adequate sensitivity and avoidance of carcinogenic benzidine derivatives, we recommend the cyanomethemoglobin method for routine use in the measurement of supernatant hemoglobin in stored modified red cell concentrates.