Hemoglobin Mass Determination: Exploring Carboxyhemoglobin Stability and Analyzer Interchangeability

ABSTRACT Carbon monoxide (CO) rebreathing is frequently used to determine hemoglobin mass (Hb mass ) during hypoxic or heat training and high‐altitude research. Accurate and reliable carboxyhemoglobin (HbCO) determination is crucial for reliable Hb mass measurements. The aim was therefore to explore the stability of HbCO and interchangeability of two Radiometer analyzers in the determination of Hb mass . Twelve subjects performed a CO rebreathing test. Five capillary blood samples were taken before and after the CO rebreathing test and either analyzed immediately on site (three capillary tubes, Day 1, ABL 90) or stored at room temperature and sent to another laboratory for analysis 4–8 days later (two capillary tubes, ABL 825). Intraclass correlation coefficient (ICC) and relative typical error (TE) were calculated to compare both measurements. A paired sample t test was performed to detect potential differences between Day 1 (ABL 90) and Days 4–8 (ABL 825). A trivial mean difference was observed between the two measurements for ΔHbCO (0.05%, p = 0.01, d = −0.12) and Hb mass (7.7 g, p = 0.01, d = 0.10). High reliability (ICC > 0.98) and low TE (< 0.91%) were found for ΔHbCO and Hb mass . Immediate analysis with the same analyzer remains recommended despite trivial differences between measurements. However, when logistical issues (analyzer breakdown, extreme, and/or remote locations) do not allow optimal procedures, delayed analysis, potentially with a different analyzer, might be used as a viable alternative.