Approximately 9% of hepatitis C infections in HIV-positive
individuals are missed by some rapid hepatitis C testing assays, US
investigators report in the September 15th edition of the Journal of Infectious Diseases.
Three rapid tests were evaluated in the study. The
OraSure assay had a very low rate of false-negative results. However, the two
remaining assays had an overall false negative rate of 8.5% in HIV-positive
patients, a significantly higher rate than that observed in HIV-negative
Although the confidence intervals were wide and the estimate of the false-negative rate therefore imprecise, the investigators say that further evaluation is needed in a larger HIV-positive population.
However, overall the rapid assays performed well, having a
sensitivity of between 87% and 96% and a specificity of almost 100%.
“Anti-HCV [antibody hepatitis C virus] rapid assays could be
implemented in many settings,” suggest the investigators, “hard-to-reach, high-risk
populations, such as persons who inject drugs, are unlikely to be screened for
anti-HCV using conventional testing, and when they are, they are less likely to
return for their results.”
It is estimated that between 50% to 70% of the US’s 3.2
million hepatitis C infections are undiagnosed.
Guidelines recommend routine antibody testing for patients
at high risk of hepatitis C. However, many hepatitis C-infected individuals
belong to marginalised or hard-to-reach populations who do not access conventional
Rapid antibody tests are incorporated into HIV screening
services and research indicates that individuals receive their HIV test results
more often when they have a rapid test rather than a conventional test (83-100%
Investigators therefore evaluated three rapid hepatitis C
antibody tests capable of delivering a result in less than 40 minutes.
The Chembio DPP HCV Test screens for hepatitis C using whole
blood, serum, plasma, or oral fluid. The time required to perform the assay is
between 15 and 30 minutes.
The Multiplo Rapid HIV/HCV (MedMira) Antibody test uses
whole blood, serum or plasma samples and can deliver a result within three
The OraQuick HCV Rapid Antibody Test can detect antibodies
using blood samples from a finger stick, oral fluid collected using a swab, or
whole blood, serum or plasma obtained using a conventional blood test. This
assay has been licensed in the US.
Using 1100 stored blood samples obtained from injecting drug
users between 1997 and 1999 the investigators evaluated the reliability of the
Just under than half the samples (49.7%) were positive for
hepatitis C antibodies and the remaining 50.3% were negative.
Performance of the rapid tests was compared against the
standard antibody screening assay and the Centers for Disease Control (CDC)
Compared to standard antibody screening, the rapid assays
had a sensitivity of between 87% and 98%, and their specificity ranged from
99.6% to 99.8%.
Sensitivity of Orasure (97.8%) was significantly higher than
both Chembio (96.2%, p = 0.012) and MedMira (87%, p < 0.01).
Using the CDC testing approach, sensitivity ranged from 88%
to 99% and the specificity between 99.5% and 99.8%. Once again, sensitivity was
higher for OraSure (99.3%) compared to Chembio (97.8%, p = 0.021) and MedMira
(88%, p < 0.001).
Rates of false positives and false negatives varied between
the assays and reference approaches.
Chembio had 0.2% false positives and between 2.2% and 3.9%
The rate of false positives using MedMira was 0.2%, with
between 11.7% and13.4% being false negative.
OraSure had between 0.4% and 0.6% with a false positive result
and 0.7% to 2.2% had a false-negative result.
Infection with HIV was significantly associated with false
results for both the Chembio (p < 0.01) and MedMira (p < 0.01) assays,
but not OraSure.
“Controlling for all other variables, specimens from
HIV-positive persons were 11 times more likely to have a false result than
those from HIV-negative persons using the Chembio test, and 4 times more likely
using the MedMira test,” write the authors.
However, they note “the sample of HIV-positive specimens
(both anti-HCV positive and negative) was small (n = 43), and the associated estimates imprecise.”
They suggest, “anti-HCV rapid assays need to be evaluated
using an HIV-positive specimen panel to establish and expected proportion of
false-negative results. Also, demonstration projects should be conducted to see
how these assays would be implemented in HIV settings.”