The evaluation of validity a portable clinical analyzer for the determination of blood ionized calcium concentration in cattle

Information on reliability of the i-STAT, a point-of-care (POC) device, to determine blood ionized calcium (iCa2+) concentration is limited. Rapid determination of blood iCa2+ concentration can help evaluation of calcium status and delivery of effective therapy in field conditions. The goal of this study was to evaluate reliability of the i-STAT (Abbott Point of Care, Abbott Laboratories, Chicago, IL) in measuring blood iCa2+ concentration in cattle. In this prospective study 121 cattle with various diseases were used. Venous blood samples were run the i-STAT and the Radiometer ABL 800 (Radiometer, Copenhagen, Denmark) analyzer for determination of blood iCa2+ concentration. Data were subjected to paired Student t-test, concordance analysis, Passing-Bablok regression and Bland-Altman plots for comparison, accuracy, agreement and reliability. The Radiometer ABL 800 was reference method however the i-STAT was the test method. The i-STAT performance was also evaluated at two different cut-off values for blood iCa2+ concentration (< 1 mmol/L; <1.18 mmol/L) using the receiver operating characteristics (ROC) curve. The mean blood iCa2+ concentration measured by the i-STAT was similar to the mean blood iCa2+ concentration measured by the Radiometer ABL 800 (1.09 versus 1.09 mmol/L; P = .82). The i-STAT results were highly correlated with the Radiometer ABL 800 results (r= 0.98, P < .0001). Regression equation fitting blood iCa2+ concentration measured by the i-STAT (Y) and blood iCa2+ concentration measured by the Radiometer ABL 800 (X), was Y= -0.108276+1.103448× X, with a residual deviation (RSD) of 0.02. The deviation from the identity line was not significant (P = .64). The Bland-Altman difference plot revealed that the mean bias was zero. The i-STAT had Se of 100 % (95% CI, 87,7 - 100,0) and Se of % 94.8 (95 % CI, 87.2-98.6) at the cut-off blood iCa2+ concentration < 1 and < 1.18 mmol/L, respectively. The i-STAT yielded precise and accurate blood iCa2+ results in cattle. The i-STAT especially predicted hypocalcemia with high sensitivity. Key Words: calcium, dairy cow, point-of-care (POC), sensitivity.