The Correlation between the S/CO Ratio of Anti-HCV ELISA, and the Results of the RIBA and RNA Test

Oh, Deok Ja

Abstract

BACKGROUND: Recombinant immunoblot assay (RIBA) or RNA test is considered to be a supplemental test for confirming a HCV infection. A correlation has been reported between the signal-to-cutoff (S/CO) ratios of a third generation HCV enzyme-linked immunosorbent assay (ELISA) and a confirmed HCV infection. This study examined the results of an evaluation of domestic anti-HCV EIA and immunoblot kit (RIBA) in Korean donors.
METHODS
A total of 375,576 donor samples were tested for anti-HCV using the LG third generation HCV ELISA (LG HCD 3.0 TMB, LGphD, Korea) and HCV RNA by NAT (Biomerieux/Roche RT-PCR, 24 pool). The anti-HCV repeat reactive samples were further tested by third generation RIBA (LG HCD Confirm, LGphD, Korea). A positive result by either the nucleic acid amplification test (NAT) or RIBA was interpreted as a confirmed HCV infection.
RESULTS
There were 506 out of the 375,576 donor samples (0.13%) that were anti-HCV repeat reactive (RR) by routine screening ELISA. The confirmed HCV prevalence in the donors was 0.01% (RIBA 42/375,570, RNA 36/375,570). 443 samples from the 506 repeat reactive samples in ELISA (87.6%) showed a S/CO ratio <3.0 but did not show positivity in the RIBA and RNA test. The rate of RIBA positivity in the RR specimens was 8.3% (42/506). The RNA detection rate in the RIBA positive samples was 85.7%(36/42). All 36 samples showing a positive result in both the RIBA and RNA test showed a significantly high S/CO ratio, >3.6 (mean 4.40+/-0.80), compared with the negative group (mean 1.54+/-0.64).
CONCLUSION
There was a good correlation between a high S/CO ratios and a confirmed HCV infection. In addition, samples showing a low S/CO ratio with an ID (Indeterminate) or negative RIBA result suggest a high probability of nonspecific reactivity in ELISA.