ROC-Based Assessment of ELISA System Used to Detect IgMRF,
IgG-RF and IgA-RF among Iraqi Rheumatoid Arthritis
Patients
Abstract
Serological tests are mainly evaluated by determining the sensitivity and specificity of the
test. These test characteristicswere 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
cut-off 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 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.
