Usefulness of P(50,std) for the Diagnostic Work-up of Patients with Erythrocytosis

ABSTRACT

High oxygen-affinity hemoglobin (Hb) variants and a 2,3-diphosphoglycerate (2,3-DPG) deficiency could cause congenital (familial) erythrocytosis. High oxygen-affinity Hb variants and a 2,3-DPG deficiency might result in low tissue oxygen tension left-shifted oxygen dissociation curves and reduction in the standard P₅₀ value (P(50,std), oxygen tension at which haemoglobin is 50% saturated). Hence, the P(50,std) value is considered while formulating diagnostic strategies for erythrocytosis. In this study, we established a reference range for P(50,std) using an International Federation of Clinical Chemistry and Laboratory Medicine-approved equation (Hill's equation) for individual single venous/arterial blood samples. Blood gas analysis results of 243 samples with oxygen saturation ranging from 40%–90% (Hb < 16 mg/dL) were selected. The reference range of P(50,std) was in the 2.5th–97.5th percentile, and was 25.9–27.3 mm Hg. Hill's equation is a simple approved method for evaluating the P(50,std) values. Only a single sample of venous or arterial blood and a blood gas analyser are required to obtain the P(50,std). Our study provides a useful tool for the diagnostic work-up of patients with erythrocytosis.