Evaluation of the i-STAT system: a portable chemistry analyzer for the measurement of sodium, potassium, chloride, urea, glucose, and hematocrit.

OBJECTIVE

To evaluate the analytical performance of the i-STAT system, which is designed for point of care testing and employs a hand-held chemistry analyzer and disposable cartridges, which in the configuration tested, are capable of measuring sodium, potassium, chloride, urea, glucose, and hematocrit in approximately 65 microL of blood in 90's.

METHODS

Linearity and imprecision in hematocrit measurement were assessed using whole blood, while that for the other analytes were evaluated with aqueous solutions. The accuracy of the i-STAT system was judged by assay of patient specimens obtained both by venipuncture and fingerprick and correlated with the Kodak Ektachem 700XR and the microhematocrit methods.

RESULTS

Linearity was obtained over the clinically relevant range for all analytes. Total imprecision as expressed by the coefficient of variation (CV) was less than 3.5% for all analytes at both high and low concentration except for a low concentration of urea where a CV of 9.4% was obtained. Linear regression analysis revealed minimal systematic errors. The standard error about the regression line (Sy/x) ranged from 0.017 for hematocrit to 2.262 for chloride in the assay of venous blood, whereas in the assay of capillary blood the Sy/x ranged from 0.018 for hematocrit to 0.755 for glucose.

CONCLUSIONS

The analytical performance of the i-STAT was deemed acceptable by calculation of total error and comparison with published performance standards. Our study has shown the i-STAT system to be reliable, robust, and simple to operate. Moreover, the compactness of the analyzer and the requirement for only small volumes of whole blood will make it a valuable diagnostic tool in point of care settings.