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Very low hepatitis C antibody levels predict false‐positive results and avoid supplemental testing
Author(s) -
Contreras Ana M.,
TorneroRomo Claudia M.,
Toribio José G.,
Celis Alfredo,
OrozcoHernández Axel,
Rivera P. Kristian,
Méndez Claudia,
HernándezLugo M. Isabel,
Olivares Laura,
Alvarado Martha A.
Publication year - 2008
Publication title -
transfusion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.045
H-Index - 132
eISSN - 1537-2995
pISSN - 0041-1132
DOI - 10.1111/j.1537-2995.2008.01886.x
Subject(s) - medicine , receiver operating characteristic , cutoff , gold standard (test) , hepatitis c virus , antibody , confidence interval , false positive rate , false positive paradox , viremia , hepatitis c , false negative reactions , gastroenterology , immunology , window period , serology , virus , statistics , mathematics , physics , quantum mechanics
BACKGROUND: False‐positive results for hepatitis C virus antibody (anti‐HCV) occur with unacceptable frequency in low‐prevalence populations. The purpose of the study was to determine whether signal‐to‐cutoff (S/CO) ratios of anti‐HCV assay–reactive samples could be used to discriminate false‐positive from true‐positive anti‐HCV results and avoid the need for supplemental testing. STUDY DESIGN AND METHODS: Using receiver‐operating characteristic curve, the cutoff point that identifies the major proportion (≥95%) of false‐positive results, with a minor proportion (<5%) of true‐positive anti‐HCV results, was determined. An anti‐HCV assay (VITROS, Ortho Clinical Diagnostics) was used to detect the antibodies. The third‐generation recombinant immunoblot assay and HCV RNA tests were performed on all included donors. Third‐generation RIBA is the gold standard for identifying false‐positive antibody results. RESULTS: A total of 649 anti‐HCV–positive blood donors were identified. A S/CO ratio of less than 4.5, defining very low levels in this value, was the optimal cutoff point to identify false‐positive results; 315 of 322 samples with very low levels were false‐positive anti‐HCV results (97.8%; 95% confidence interval [CI], 95.8%‐99.0%) and 7 were true‐positive (2.2%; 95% CI, 1.0%‐4.3%). Viremia was detected in none of them. A direct relationship was observed between positive supplemental testing and increased antibody levels in the other 327 samples. CONCLUSION: The high prediction rate of false‐positive anti‐HCV results using very low levels by the Ortho VITROS anti‐HCV assay safely avoids the need for supplemental testing.