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Single ELISA is Adequate, Even When Results are Weak
A single enzyme linked immunosorbent assay (ELISA) determination is all
that is needed for the diagnosis of hepatitis C virus infection, according
to a report from France.
Researcher Jean-Michel Pawlotsky and colleagues suggest that, due to
advances in the assay, confirmation of positive or weakly positive ELISAs
with immunoblot-based confirmatory assays is not needed.
The first-generation group of anti-hepatitis C virus (HCV) ELISAs lacked
sensitivity as well as specificity, and for this reason confirmatory assays
based on immunoblot testing were developed and systematically used to
confirm positive samples.
Since the early 1990s, however, ELISA assays have considerably improved,
and the second- or third-generation tests available today are both highly
sensitive and specific. Second- or third-generation immunoblot tests are
still used for confirmation in most laboratories, however.
The aim of this study was to determine whether a double ELISA determination
and confirmation of positive ELISA results with immunoblot assays are
still useful in clinical laboratories performing routine diagnosis of
HCV infection ("What Strategy Should Be Used for Diagnosis of Hepatitis
C Virus Infection in Clinical Laboratories?" Hepatology, June 1998;27(6):1700-1702).
Anti-HCV antibodies were sought in 3,014 consecutive unselected samples
with two different ELISAs. An immunoblot-based confirmatory assay (RIBA3.0)
was performed in the samples with at least one ELISA positive or weakly
positive. HCV RNA was evaluated using HCV polymerase chain reaction (PCR)
in the samples with a weakly positive ELISA, discrepant results of the
two ELISAS, or an indeterminate RIBA3.0 pattern.
The two ELISAs gave concordant results in 2,957 (98.1 percent) of the
3,014 samples (negative in 87.9 percent, positive in 11.8 percent, and
weakly positive in 0.3 percent), and discrepant results in 57 (1.9 percent).
RIBA3.0 was positive in 338 of the 350 ELISA-positive samples (96.6 percent)
and indeterminate in 12. Six of them were PCR-positive.
Among the eight weakly positive samples, one was RIBA3.0-positive, six
were RIBA3.0-indeterminate, and one was RIBA3.0-negative; all were PCR-negative.
Among the 57 samples with discrepant ELISA results, four were RIBA3.0-positive
(none were PCR-positive), 22 were RIBA3.0-indeterminate (one was PCR-positive),
and 31 were RIBA3.0-negative (six were PCR-positive). In these cases,
the clinical context and PCR detection of HCV RNA allowed for definitive
classification.
Pawlotsky et al. proposed the adoption of a cost-saving diagnostic procedure
for patient suspected of having HCV infection or for those with a risk
for parenterally acquired viral infections. They suggested that:
† Screening should be based on one single second- or third-generation
ELISA.
"Confirmation of positive ELISAs by ELISA on a second different sample
might be useful to avoid false-positive results owing to sampling or processing
errors," they wrote.
†No immunoblot-based confirmatory assay is needed.
† HCV RNA detection by PCR should be performed in the samples with
an OD ratio in ELISA between 1 and 2, or when knowing the replicating
status of HCV is needed for clinical decisions. This includes the classical
indications of qualitative HCV RNA PCR, i.e., seronegative acute or chronic
hepatitis of unknown cause, chronic liver disease with several possible
causes including the presence of HCV antibodies, chronic hepatitis C with
repeatedly normal alanine aminotransferase activity, diagnosis of HCV
infection in babies born to HCV infected mothers, and antiviral therapy
monitoring.
"This diagnostic procedure has been recently recommended by the French
Consensus Conference on HCV," Pawlotsky et al. wrote. "In our laboratory,
where about 8,000 HCV serological tests are performed every year, this
would allow a savings of U.S. $65,000 in reagent costs per year, not including
materials and lab work. Similar evaluations of diagnostic strategies in
the setting of blood donation screening are now needed."
The corresponding author for this study is Jean-Michel Pawlotsky, Service
de Bacteriologi-Virologie, Hopital Henri Mondor, 51 avenue du marechal
de Lattre de Tassigny, 94010 Creteil, France. - by Salynn Boyles, Senior
Editor
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