Evaluation of the IRMA TRUpoint and i-STAT creatinine assays

The i-STAT (Abbott Diagnostics, East Windsor, NJ) and IRMA TRUpoint (ITC, Edison, NJ) POCT analyzers were evaluated in an oncology center.

Precision and agreement with our core laboratory creatinine was judged by comparison of 50 consecutive chemotherapy patient results against the Roche rate-blanked Jaffe and enzymatic creatinine methods. Glomerular filtration rate (GFR) was estimated using the Cockroft-Gault (CG) calculation and Modification of Diet in Renal Disease Study (MDRD) equation.

Precision varied from 1% (enzymatic)-6.1% (TRUpoint). Correlation was good (r>0.9948) with slopes within 5% of the Jaffe and enzymatic methods. Intercepts were <15.9 micromol/l (<0.18 mg/dl), and statistically significant bias (p<0.0025) was noted between the mean of patient specimens for i-STAT correlations to both the Jaffe and enzymatic laboratory creatinine methods. There was statistically significant concordance of estimated GFR between all methods, however, the agreement of estimated GFR to either the Jaffe or enzymatic creatinine laboratory methods was better for the TRUpoint (by either MDRD or CG estimation) and i-STAT (by MDRD equation) (Kappa>0.60) than the i-STAT (by CG estimation) (Kappa=0.41-0.60).

Small biases in the calibration of analytical creatinine methods can lead to differences in clinical concordance using estimated GFR. Selecting an optimal POCT method depends on the institution's current creatinine method and tolerance for analytical performance and clinical concordance.