RESUMO
Patients with hepatitis C virus (HCV) infection are detected by testing for the presence of antibodies to HCV (Anti-HCV). A positive Anti-HCV test represents a true positive result only in a variable proportion of subjects (35 to 95%). The qualitative interpretation as positive or negative Anti-HCV report is associated with a general lack of understanding regarding the interpretation of results, when more specific testing should be performed, and which tests should be considered for this purpose. Therefore, a substantial variation in supplemental testing practices exists among laboratories and physicians. This guideline was developed on the basis of the best available evidence to classify positive antibody in two (low and high) or three levels (very low, low and high) according to the signal to cutoff (S/CO) ratio: the very low level of the Anti-HCV identifies false-positive results and further diagnostic testing is not necessary. The low antibody level is frequently related with false-positive results and testing with Immunoblot is recommended; only Immunoblot-positive subjects require HCV RNA testing because of a low possibility of being viremic. The high Anti-HCV level is an accurate serological marker for predicting viremia and denotes the need of routine HCV RNA testing in order to efficiently confirm hepatitis C. Cost-effectiveness analysis, based on the Anti-HCV level, recommends the use of the two or three-levels to choose the confirmatory test of positive antibody. This approach can be implemented without increasing test costs because the S/CO ratio is automatically generated in most laboratory analyzers and would provide health care professionals with useful information for counseling and evaluating patients, to eliminate unwarranted notifications in cases of false antibody reactivity, and correctly identifying those Anti-HCV-positive patients who are infected and need antiviral treatment. The written report should include the antibody level (S/CO ratio), the type of the immunoassay applied and interpretation guideline. Anti-HCV testing is performed in multiple settings including blood banks or health department facilities; adoption of this Guideline for interpretation and report of the antibody to hepatitis C virus by laboratories and its implementation by clinicians will improve the accuracy for interpreting antibody result to determine the next step on hepatitis C diagnosis.
