Roles of Malondialdehyde, Glutathione Peroxidase and N-Acetyl-ß-D-glucosaminidase in Serum of Urolithiasis

Abstract EN

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 adiagnostic 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 use.