C-reactive protein (CRP) is a widely recognized indicator of inflammation. Prospective studies have shown that CRP can be used to predict the risk of future cardiovascular events in apparently healthy subjects. Clinical and laboratory studies have also shown that inflammation has an important role in the inititation, progression and destabilization of atheromas, which makes high-sensitivity CRP determinations valuable in cardiovascular risk assessment. Innotrac Aio! is a fully automated random-access immunoanalyzer using a unique all-in-one (Aio!) dry reagent concept and time-resolved fluorometric detection. In this study, the analytic performance of the Innotrac Aio! ultrasensitive CRP assay (usCRP) was evaluated. The analytical detection limit was 0.003 mg/L, the limit of quantification was <or= 0.03 mg/L and the carry-over result was within acceptable limits. Within-assay CVs obtained in lithium-heparin plasma at five concentrations ranged within 3.2 and 24.9%. Inter-assay precision using lithium-heparin plasma pools and commercial controls was 6.2-8.6% at concentrations of 0.17-33.3 mg/L. The inter-assay precision at a concentration of 0.04 mg/L using the serum pool was 67%. Regression analysis between Aio! usCRP and Cobas Integra CRP latex (Roche Diagnostics) using lithium-heparin plasma samples yielded the following results: correlation coefficient 0.983, slope 1.17 (< 50 mg/L) and correlation coefficient 0.974, slope 1.137 (< 10 mg/L). The correlation coefficient between Integra and Aio! usCRP assays using serum samples was 0.979 and the slope 1.106. Regresssion analysis between Aio! usCRP and Hitachi CRP (Latex) HS using serum samples revealed the following results: correlation coefficient 0.942, slope 0.879 (< 20 mg/L) and correlation coefficient 0.973, slope 0.983 (< 10 mg/L). EDTA whole blood samples correlated well with the corresponding plasma samples. Innotrac Aio! usCRP assay was found to be linear in the CRP concentration range of 0.09-62 mg/L. In the first quartile (0-25th percentile), 2nd quartile (25th-50th percentile), 3rd quartile (50th-75th percentile) and 4th quartile (75th-100th percentile), the mean CRP values were 0.16 mg/L, 0.52 mg/L, 1.24 mg/L and 4.39 mg/L, respectively.