Reference interval, longitudinal variability and reliability of activated clotting time in healthy dogs using a point‐of‐care analyser

Abstract Background Activated clotting times (ACTs) are used to screen for coagulopathies and monitor heparin therapy. Objectives To determine a reference interval (RI) for ACT in dogs using a point‐of‐care analyser, to quantify intra‐subject within‐ and between‐day variability, to quantify analyser reliability and inter‐analyser agreement and to study the influence of a delay in measurement. Methods Forty‐two healthy dogs were included. Measurements were performed on fresh venous blood using the i‐STAT 1 analyser. The RI was determined using the Robust method. Intra‐subject within‐day variability and between‐day variability were quantified between baseline and 2 h ( n = 8) or 48 h ( n = 10) later. Analyser reliability and inter‐analyser agreement were studied by duplicate measurements ( n = 8) on identical analysers. The influence of measurement delay was studied before and after a delay of one analytical run ( n = 6). Results Mean, lower and upper reference limits for ACT were 92.9 ± 9.1, 74.4 and 111.2 s, respectively. Coefficients of variation of intra‐subject within‐ and between‐day variability were 8.1% and 10.4%, respectively, resulting in a significant between‐day measurement difference. Analyser reliability assessed by the intraclass correlation coefficient and coefficient of variation were 0.87% and 3.3%, respectively. Significantly lower ACT values were observed after a measurement delay compared to direct analysis. Conclusions Our study provides an RI for ACT in healthy dogs using the i‐STAT 1 and suggests low intra‐subject within‐ and between‐day variability. Analyser reliability and inter‐analyser agreement were good; however, analysis delay and between‐day differences could significantly influence ACT results.