Rejection of prospective blood donors due to systematic errors in hematocrit measurement.

Following a change from earstick to fingerstick hemoglobin estimations, donor deferrals increased from 8.8% to 13.6%. Coincident with the change to fingersticks, hematocrit measurement with miniature centrifuges was begun as the reference method to verify donor rejection by the copper sulfate test. A study of 525 donors deferred for fingerstick hematocrits showed that 46.7% were deferred inappropriately as determined by venous hematocrit measurements. The difference between fingerstick and venous hematocrits persisted even after an intensive staff inservice on technique. In further studies, no significant difference was found between venous and fingerstick hematocrits measured on the same centrifuge, but there was a significant difference between measurements on the miniature centrifuges versus a standard laboratory microhematocrit centrifuge. This small error resulted in the loss of 3.8% of presenting donors during the study period. Hematocrit measurements have now been replaced by a fingerstick cyanmethemoglobin method.