Accuracy of point-of-care-testing (POCT) for determining hemoglobin concentrations

Background: While point‐of‐care testing (POCT) is being used increasingly as a basis for deciding on perioperative erythrocyte transfusion, no valid standards currently exist concerning the accuracy of Hb concentration measurements. For clinical employment, however, the confidence limits (±2 SD) of these measurements should lie close to 5 g/l. The aim of the present study was to evaluate the accuracy and precision of point‐of‐care testing for blood hemoglobin concentration (cHb in g/l) measurements in critically ill patients. Methods: Fifty blood samples from 50 postoperative patients requiring intensive care treatment were withdrawn from a cannula in the radial artery into a 2‐ml heparinized syringe (containing wet sodium heparinate in the conus), in a 2‐ml Monovette with 50 IE lithium heparinate, and into a 2.7‐ml cuvette with 1.6 mg potassium EDTA/ml blood. The POCT battery consisted of two blood gas analyzers (ABLTM 625 and 725, Radiometer, Copenhagen), the HemoCue® system (Mallinckrodt Medical, Germany), and an automated hematology analyzer (M‐2000®, Sysmex, Germany). The cyanmethemoglobin method served as the reference ‘gold standard’ procedure. The blood gas analyzer and HemoCue® systems were tested using dry and wet heparinized blood samples. Results: Hemoglobin concentrations of the reference measurements ranged from 73.9 to 159.4 g/l. The automated hematology analyzer method did reveal a small but systematic deviation for higher cHb values. For the blood gas analyzer and HemoCue® system procedures there was no systematic deviation of bias for either the first measurement or the averaged data. Bland & Altman analysis revealed a larger scattering for the wet heparinized samples. Conclusions: The above‐stated requirement for POCT systems, i.e. that the confidence limits should lie close to 5 g/l cHb, held true for the dry heparinized samples of the blood gas analyzer (1st measurement and mean of 2), the HemoCue® system (mean of 3) and the automated hematology analyzer.