Reliability of the i‐STAT for the determination of blood electrolyte (K+, Na+, and CI −) concentrations in cattle

BACKGROUND Rapid determination of blood electrolyte concentrations can help determine electrolyte status and delivery of effective volume of electrolyte solutions in field conditions. OBJECTIVE To evaluate reliability of the i-STAT, a point-of-care (POC) device, in measuring blood K(+), Na(+), and CI(-) concentrations in cattle. ANIMALS Ninety-eight cattle with various diseases. METHODS In this prospective study, blood samples collected from the jugular vein were processed for determination of K(+), Na(+), and CI(-) concentrations in blood and plasma using the i-STAT and auto-analyzer (Cobas C501), respectively. Blood and plasma electrolyte data were subjected to student t-test for comparison, the concordance analysis for agreement, accuracy, and precision, the Passing-Bablok regression and the Bland-Altman plot for reliability, and receiver operating characteristics curves for sensitivity (Se) and specificity (Sp). RESULTS Plasma concentrations of K(+) (4.39 versus 4.2 mmol/L; P < .0001) and CI(-) (100.30 versus 99.4 mmol/L; P < .04) were greater than their concentrations in blood. Plasma and blood Na(+) concentrations were similar (136.95 versus 136.8 mmol/L). The i-STAT results were highly correlated with the Cobas C501 results (r = 0.970, 0.922, and 0.866 for K(+), Na(+), and CI(-), respectively). Regression equations fitting blood (Y) and plasma (X) concentration did not deviate from the identity line for K(+) (Y = -0.10 + 0.98 × X), Na(+) (Y = X), and CI(-) (Y = 3.04 + 0.96 × X). The mean bias (blood concentration - plasma concentration) was -0.20 for K(+) (P = .03), -0.16 for Na(+) (P = .12), and -0.87 for CI(-) (P = .93). The i-STAT had 76-100% Se and 87.7-100% Sp for assessing electrolyte statuses. CONCLUSIONS AND CLINICAL IMPORTANCE The i-STAT yielded results that were in agreement with the auto-analyzer, with negligible biases in measurement of plasma K(+), Na(+), and CI(-) concentrations. The i-STAT is a reliable POC device and can be used in field condition to assess electrolyte status in cattle.