Hematocrit estimates comparing centrifugation to a point-of-care method in beef cattle living at high altitude

Background: The hematocrit (Hct) or packed cell volume (PCV) reflects the blood volume occupied by red blood cells. The development of point-of-care (PoC) instruments can accelerate the ease of measuring Hct/PCV compared with traditional capillary centrifugation (TCC) methods. However, no studies have compared Hct/PCV levels in cattle at high elevation with other measurement methods. Objectives: In this study, we aimed to compare methods to estimate Hcts/PCVs of rangeland cattle at high elevation. We specifically wanted to determine if Hct/PCV levels measured with a commercial PoC instrument (i-Stat with CHEM8+ cartridges [PoCi]) were comparable to Hct/PCV levels measured with traditional laboratory methods. Methods: We assessed the Hct/PCV of 94 mature beef cattle (black Angus; Bos taurus) at similar to 2195 m above sea level using paired analyses of the PoCi and TCC methods from each animal. We used paired samples t-tests to compare mean Hct/PCVs. Correlation analyses relative to the line of identity and Passing-Bablok regression were used to assess systematic and proportional differences, respectively, and Bland-Altman plots were used to assess agreement between the two methods. Results: The PoCi estimated a Hct of 28.2% +/- 0.7% (SE), which was lower than the TCC estimated PCV of 39.2% +/- 0.5%. The Bland-Altman plot revealed poor agreement between the two methods in addition to a -11% bias for the PoCi. The Passing-Bablok regression revealed both systematic and proportional bias between the two methods. Conclusions: Point-of-care blood instruments were not comparable to TCC methods for quantifying Hct/PCVs of cattle living at high elevations.