TY - JOUR T1 - Does venous blood gas analysis provide accurate estimates of hemoglobin oxygen affinity? JF - European Respiratory Journal JO - Eur Respir J VL - 38 IS - Suppl 55 SP - 4880 AU - Fabienne Huber AU - Tsogyal D. Latshang AU - Jeroen Goede AU - Konrad E. Bloch Y1 - 2011/09/01 UR - http://erj.ersjournals.com/content/38/Suppl_55/4880.abstract N2 - Background: Polycythemia occurs in conditions with chronic hypoxemia including lung and heart disease, polycythemia vera, hemoglobinopathies and in certain neoplasms. Arterial blood gas analysis and assessment of hemoglobin oxygen affinity by the PO2 with oxygen saturation of 50% (P50) are used to evaluate potential causes of secondary polycythemia. We investigated accuracy of a simplified estimation of P50 from venous blood in comparison to tonometry, the gold standard for measurement of P50.Methods: In 50 patients referred for evaluation of polycythemia pH, PO2 and SO2 were measured in venous blood (ABL 700 series, Radiometer, Copenhagen) and P50v was derived by standard equations (Severinghaus, J Appl Physiol 1979;46:599). Tonometry was performed to obtain P50t (Hemoxanalyzer, TCS, New Hope, PA). Agreement of P50v and P50t was analyzed.Results: The mean P50t was 25.8 (range 17.4-34.1) mmHg. The mean difference (bias) of P50v and P50t was 0.5 mmHg, the limits of agreement (95% CI) were -5.15 to +6.09 mmHg. The sensitivity and specificity of P50v to identify patients with P50t outside the normal range (23-27 mmHg) were 5 and 77%, respectively.Conclusions: Estimates of P50 based on venous blood gas analysis and standard equations have a low bias compared to tonometry. However, the precision of P50v is not sufficiently high to replace P50t in the evaluation of individual patients with suspected disturbances of hemoglobin oxygen affinity. ER -