ROC-Based Assessment of ELISA System Used to Detect IgM-RF, IgG-RF and IgA-RF among Iraqi Rheumatoid Arthritis Patients

Mohanad Ahmed, Khalid Al-Ruhaimi, Suhad Mohammed, Hassan Al Saadi, Shawahd Al-Yassiri, Nidahl Abdul-Ameer, Salah Al-Ali
Serological tests are mainly evaluated by determining the sensitivity and specificity of the test. These test characteristics were originally meant to be used in making diagnoses. For evaluative purposes their usefulness is weakened by their susceptibility to selection and their dependence on the cutoff points that are used for test positivity. The plotting of a receiver operating characteristic (ROC) curve might be a solution to these problems. The ROC curve yields a measure for the diagnostic
more » ... for the diagnostic power of the test expressed in one number instead of two, namely the area under the curve (AUC). Furthermore, the ROC curve and its AUC permit easy comparison of different tests and the performance of different interpreters of one test. In this study, for direct comparison of the diagnostic values of IgM-RF, IgG-RF and IgA assay in the diagnosis of Rheumatoid Arthritis (RA), we performed an ROC analysis. The calculated areas under curves (AUCs) have shown that each of the three RF-subtypes has a different discriminative value because their curves were located at different distances above the diagonal line. However, the IgG-RF subtype has the highest discriminative value because of that its AUC was 0.937 and, thus, it has a very high clinical value. IgM-RF subtype has a moderate discriminative value (AUC= 0.848), whereas IgA-RF has showed the least discriminative power (AUC= 0.709) that may make it the least clinically useful RF as a diagnostic test. These results clearly demonstrate the superiority of IgG-RF ELISA system as a diagnostic test for RA over the other RFs. Using ROC to determine cutoff values has yielded several cutoff values with variable sensitivities and specificities for each RF subtype. This may allow the choice of the desired cutoff according to the clinical setting in which the test might used. ‫ﺍﻟﺨﻼﺼﺔ‬ ‫ﻨﻔﺴﻬﺎ‬ ‫ﻋﻥ‬ ‫ﺘﻌﺭﺏ‬ ‫ﻭﺍﻟﺘﻲ‬ ‫ﻟﻼﺨﺘﺒﺎﺭﺍﺕ‬ ‫ﺍﻟﺘﺸﺨﻴﺼﻴﺔ‬ ‫ﻟﻠﻘﻭﺓ‬ ‫ﻗﻴﺎﺴﺎ‬ ‫ﻴﻨﺘﺞ‬ ‫ﺍﻟﻤﺼﻠﻴﺔ‬ ‫ﻟﻸﺨﺘﺒﺎﺭﺍﺕ‬ ‫ﺍﻟﻤﺘﻠﻘﻲ‬ ‫ﺘﺸﻐﻴل‬ ‫ﻤﻨﺤﻨﻰ‬ ‫ﺭﺴﻡ‬ ‫ﺍﻥ‬ ‫ﺍﺜﻨﻴﻥ‬ ‫ﻤﻥ‬ ‫ﺒﺩﻻ‬ ‫ﻭﺍﺤﺩ‬ ‫ﺒﺭﻗﻡ‬) ‫ﻭﺍﻟﻨﻭﻋﻴﺔ‬ ‫ﺍﻟﺤﺴﺎﺴﻴﺔ‬ (‫ﺍﻟﻤﺨﺘﻠﻔﺔ‬ ‫ﻟﻸﺨﺘﺒﺎﺭﺍﺕ‬ ‫ﺍﻟﻤﻘﺎﺭﻨﺔ‬ ‫ﺴﻬﻭﻟﺔ‬ ‫ﻴﺘﻴﺢ‬ ‫ﻤﻤﺎ‬ ‫ﺍﻟﻤﻨﺤﻨﻰ‬ ‫ﺘﺤﺕ‬ ‫ﺍﻟﻭﺍﻗﻌﺔ‬ ‫ﺍﻟﻤﻨﻁﻘﺔ‬ ‫ﻭﻫﻲ‬ ‫ﻟ‬ ‫ﺍﻟﺘﻔﺴﻴﺭﺍﺕ‬ ‫ﻤﺨﺘﻠﻑ‬ ‫ﻭﺃﺩﺍﺀ‬ ‫ﺍﻟﻭﺍﺤﺩ‬ ‫ﻸﺨﺘﺒﺎﺭ‬. ‫ﺍﻟﻌﻭﺍﻤل‬ ‫ﻤﻥ‬ ‫ﻟﻜل‬ ‫ﺍﻟﺘﺸﺨﻴﺼﻴﺔ‬ ‫ﻟﻠﻘﻴﻡ‬ ‫ﻤﺒﺎﺸﺭﺓ‬ ‫ﻤﻘﺎﺭﻨﺔ‬ ‫ﻷﺠﺭﺍﺀ‬ ‫ﺍﻟﻤﺘﻠﻘﻲ‬ ‫ﺘﺸﻐﻴل‬ ‫ﺨﺎﺼﻴﺔ‬ ‫ﻤﻨﺤﻨﻰ‬ ‫ﺘﺤﻠﻴل‬ ‫ﺍﻟﺩﺭﺍﺴﺔ‬ ‫ﻫﺫﻩ‬ ‫ﻓﻲ‬ ‫ﺃﺠﺭﻴﻨﺎ‬ ‫ﺍﻟﺭﺜﻭﻴﺔ‬ IgG ‫ﻭ‬ IgM ‫ﻭ‬ IgA ‫ﺍﻟﻌﺭﺍﻕ‬ ‫ﻓﻲ‬ ‫ﺍﻟﺭﺜﻭﻱ‬ ‫ﺍﻟﻤﻔﺎﺼل‬ ‫ﺍﻟﺘﻬﺎﺏ‬ ‫ﻤﺭﻀﻰ‬ ‫ﻓﻲ‬. ‫ﺍﻟﻤﻨﺤﻨﻴـﺎﺕ‬ ‫ﺘﺤـﺕ‬ ‫ﺍﻟﻭﺍﻗﻌﺔ‬ ‫ﺍﻟﻤﻨﺎﻁﻕ‬ ‫ﺃﻅﻬﺭﺕ‬ ‫ﺘ‬ ‫ﻗﻴﻤﺔ‬ ‫ﺭﺜﻭﻱ‬ ‫ﻋﺎﻤل‬ ‫ﻟﻜل‬ ‫ﺃﻥ‬ ‫ﺍﻟﻤﺤﺴﻭﺒﺔ‬ ‫ﻤﺨﺘﻠﻔﺔ‬ ‫ﻤﻴﻴﺯﻴﺔ‬. ‫ﺫﻟﻙ‬ ‫ﻭﻤﻊ‬ ، ‫ﻨﻭﻉ‬ ‫ﺍﻟﺭﺜﻭﻱ‬ ‫ﺍﻟﻌﺎﻤل‬ ‫ﻓﺄﻥ‬ IgG ‫ﺘﻤﻴﻴﺯﻴـﺔ‬ ‫ﻗﻴﻤـﺔ‬ ‫ﺍﻋﻠـﻰ‬ ‫ﺃﻅﻬﺭ‬) ‫ﺍﻟﻤﻨﺤﻨﻰ‬ ‫ﺘﺤﺕ‬ ‫ﺍﻟﻤﻨﻁﻘﺔ‬ = 0.937 (، ‫ﻭﺒﺎﻟﺘﺎﻟﻲ‬ ‫ﻓ‬ ‫ﺠﺩﺍ‬ ‫ﻋﺎﻟﻴﺔ‬ ‫ﺍﻟﺴﺭﻴﺭﻴﺔ‬ ‫ﻘﻴﻤﺘﻪ‬. ‫ﻨﻭﻉ‬ ‫ﺍﻟﺭﺜﻭﻱ‬ ‫ﺍﻟﻌﺎﻤل‬ ‫ﺃﻤﺎ‬ IgA ‫ﻗﻴﻤـﺔ‬ ‫ﺍﻗـل‬ ‫ﺃﻅﻬـﺭ‬ ‫ﻓﻘﺩ‬