Rheumatoid Factor and ASO assessment by immunoturbidimetry and immunonephelometry

Rheumatoid Factor and ASO assessment by immunoturbidimetry and immunonephelometryT he utilization of specific protein tests to predict risks asso- ciated with infection and autoantibody presence has increased over the last few years.Antistreptolysin O (ASO) and rheumatoid factor (RF) tests are among the most requested tests.ASO antibodies are produced by the host after an infection with group A beta-hemolytic streptococcus.ASO is used as a serological marker to indicate a past infection, even though evidence of its usefulness is limited.ASO titers are frequently requested, especially in cases of acute tonsillitis in the pediatric population [1].RF is an autoantibody directed against gamma globulins.Rheumatoid arthritis (RA) patients have high RF levels in serum [2]; its titer mostly correlates with disease severity and predicts a poor prognosis [3,4].Specific proteins are analyzed using specialized methods such as radial immunodiffusion, immunoelectrophoresis, ELISA, dedicated immunonephelometers, or immunoturbidimeters [5].Nephelometry has traditionally been considered a reference method.The most frequently used methods for the routine measurement of serum ASO and RF are based on immunonephelometry or immunoturbidimetry.Turbidimetry and nephelometry are photometric assays commonly used to quantify immune-complex precipitates by their ability to interact with incident light [6].A special analyzer is required for nephelometric measurements, whereas turbidimetric measurements can be easily performed on a clinical chemistry analyzer.Thus, clinical laboratories may opt to shift some analyses Objectives: 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. 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.