Estimated and determined P50 values in erythrocytosis

Actual determination of the position of the oxygen-hemoglobin dissociation curve (P50) was compared to three methods of estimating P50 in 20 patients with erythrocytosis. There was a significant correlation between determined and estimated P50 values for each of the methods studied. Furthermore, four patients with high affinity hemoglobins were readily distinguished from the other patients by estimating P50. The data suggest that calculating P50 is reliable and may replace the need for actual measurement.