Rheumatoid Factor and ASO assessment by immunoturbidimetry and immunonephelometry

INTRODUCTION: In this study, ASO and RF immunoturbidimetric assays determined on the Roche Cobas analyzer were evaluated against an immunonephelometric method
METHODS: ASO and RF assays were performed with the immunonephelometric method using the Beckman Coulter Immage 800 analyzer and the immunoturbidimetric method using the Cobas c501 analyzer. Precision values of both assays were calculated using internal quality control (IQC) samples provided by the test manufacturers. In addition, to assess bias, IQC and external quality control (EQA) data were used. Method comparison studies were performed using serum specimens randomly selected from routine hospital orders.
RESULTS: Both assays demonstrated good precision for ASO, with precision values of 3.2% CV in the immunoturbidimetric assay and 5.0% CV in the immunonephelometric assay. Although the immunoturbidimetric assay for RF showed good precision, the precision of RF exceeded the desired limits in the immunonephelometric assay. Bias obtained from EQA data was excellent in both ASO and RF for the immunoturbidimetric assay. The Passing–Bablok regression equation was obtained as y=1.65x - 20, r=0.98 for ASO, and as y=1.02x - 10.9, r=0.85 for RF.
DISCUSSION AND CONCLUSION: In conclusion, ASO and RF tests on the Cobas analyzer are suitable for routine use because they meet the requirements for accuracy and precision. The imprecision of the RF assay should be improved, especially for the immunonephelometric assay.