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Dependence of hemoglobin mass estimation with the optimized CO‐rebreathing method on different spectrophotometers

The assessment of total hemoglobin mass (tHb‐mass) with the optimized carbon monoxide‐rebreathing procedure (oCOR) is discussed as a promising method to detect blood doping. The method requires repeated measurements of the carboxyhemoglobin fraction (%HbCO) using spectrophotometers (CO oximeters). In order to determine whether %HbCO measurements with different spectrophotometers yield similar tHb‐masses, the results of 57 tHb‐mass calculations from simultaneous %HbCO measurements with two different spectrophotometers (RapidLab, OSM3) were analyzed. For the comparison of longitudinal tHb‐mass alterations (ΔtHb‐mass), 3 tHb‐mass measurements were obtained at 6‐month intervals (33–37 subjects). Because of significant differences in %HbCO measurements, the limits of agreement for tHb‐massOSM3 and tHb‐massRapidLab were 11.2% (95% reference range −6.8 to +15.6%) and the correlation of ΔtHb‐masses as determined with the two spectrophotometers over two time intervals was weak (r: 0.28–0.66). In only about 70% of all ΔtHb‐mass estimations did ΔtHb‐massOSM3 and ΔtHb‐massRapidLab show the same direction of change. Apparently, the analytical variation in tHb‐mass determination with oCOR increases considerably with the use of different spectrophotometers. Therefore, agreement on the use of one spectrophotometer that accurately measures low %HbCO values is needed if oCOR should be used in an anti‐doping setting.