Agreement between hematocrits measured with electrical conductivity on the i‐STAT analyzer and manual packed cell volume measurements in 148 chelonian patients

Abstract

Point-of-care (POC) analyzers are increasingly used for diagnostic testing in exotic animals. A few studies with small sample sizes, evaluating agreement between hematocrit (Hct) and packed cell volume (PCV) measurements in chelonians, showed conflicting results. We aimed to assess the agreement between Hct values measured with a POC analyzer and manual PCV measurements in venous samples from 148 chelonians. All chelonians that underwent bloodwork for clinical reasons had Hct measured with an analyzer employing electrical conductivity (i-STAT, Abbott), PCVs measured using centrifugation, and total solids (TS) measured with refractometry. Bland-Altman plots were built to assess agreement between the measurements. Generalized linear mixed models were used to determine the effect of different variables on the difference between Hct and PCV. Of 192 chelonians sampled during this period, 148 had Hct, PCV, and TS results. Hct significantly underestimated PCV, with a mean difference between the techniques of -3.8% (95% CI: -4.5 to -3.2; LoA: -11.5 to 3.8). There was a negative correlation between the value of TS and the difference between the methods. Controlling for other factors, the magnitude of the disagreement was not affected by the sex of the chelonian but was smaller in red-eared sliders (Trachemys scripta elegans). Hct values measured with electrical conductivity in chelonians significantly underestimated manual PCVs by about 4%. This difference should be considered whenever an Hct measured on a POC analyzer using electrical conductance is used in chelonian patient assessments.