Comparison of potassium ISFETs with the Radiometer KNA1 and the Corning 902 ion selective electrode analysers for whole blood potassium ion estimation

Clinical evaluation of sodium ion selective field effect transistors for whole blood assay

Sodium ion selective field effect transistors (ISFETs) were evaluated for their performance in measurement of sodium ions in whole blood for 'near patient' analysis in operating theatres and intensive care units. Performance was evaluated in comparison with a standard clinical laboratory sodium/potassium ion analyser (Radiometer KNA1) and with sodium and potassium assays using flame photometry on the plasma from each whole blood specimen. The imprecisions (coefficients of variation) of three ISFETs for sodium ion assay were 1.08, 1.56 and 1.10%, respectively. Robust bivariate linear regression (reweighted least squares preceded by least median of squares) of the ISFET versus KNA1 sodium ion activity yielded a regression coefficient of 1.08 and an intercept of -18.2 mM. The influence of potassium, protein and lipid on the measurement of sodium ions by both ISFETs and the KNA1 was assessed using robust multiple regression (also based on reweighted least squares preceded by least median of squares). In the regression versus flame photometry, protein was found to be more influential for the KNA1 (glass sodium ion selective electrode) than for the ISFET. Potassium had no influence on assays using the ISFET, but had a weak negative influence on assays using the KNA1. Two ISFETs lasted for more than 200 assays each demonstrating their robustness in the assay of whole blood.

Performance evaluation of ISFETs and other ISE sensors for whole blood ion assay

Performance evaluations of ion-selective field-effect transistors (ISFETs) have been carried out using both quality-control materials and whole arterial blood samples. Comparison of the results from these evaluations suggests that the whole blood evaluation may be more useful when assessing the value of particular sensors for clinical applications. The effect of outliers on the imprecision estimates is demonstrated for ISFETs and ISEs, both graphically and in the calculation of the estimates with and without the outliers present. Estimates of constant and proportional bias, against an alternative sensor, determined from the intercept and slope of the linear regression vary according to the regression method used. The bias estimates obtained for the K + ISFET against the Radiometer KNA1 using ordinary least squares regression are compared with the Deming/Mandel method and the three-group resistant line method of Tukey. The Thorn EMI ISFETs are demonstrated to have acceptable imprecision and only a small bias compared with direct ISE instruments for whole blood assay and can be considered suitable for incorporation into clinical instrumentation.