Wednesday, April 25, 2012

Basic knowledge

Hepatitis C may be clinically silent for years and many people
have been infected with hepatitis C virus (HCV) for decades
without knowing it. Effective screening should focus on
populations at-risk for HCV infection. Hepatitis C is diagnosed by
simple blood tests (Dufour 2000) (Table 2.1):
Detection of HCV antibodies is done by enzyme immunoassay
(screening tests) and immunoblot (confirmation tests). A new
HCV rapid test device (OraQuick® HCV Rapid Antibody Test), was
approved recently in Europe for use with venous or fingerstick
blood, serum, plasma or oral fluid (Lee 2011). This may help
address the problem of under-diagnosis, by increasing testing
outside of traditional clinical settings. However, all these
techniques have a window-period limitation (due to the late
seroconversion), which can last 70-82 days, considerably
reducing their usefulness in the diagnosis of acute HCV
infection. Testing for anti-HCV may be performed at 18 months
of age or older (before this age there is a high rate of false
Patients’ monitoring during and after treatment | 31
positive results, due to passive antibodies transfer from the
mother).
Nucleic acid testing (NAT) – detection of presence and/or
amount (viral load – VL) of HCV RNA in the blood, reflects the
actual viral replication. These tests are the hallmark of HCV
diagnosis in both antibody-positive and negative patients, with
unexplained ALT elevations or liver disease documented by liver
biopsy (LB). A high VL is a negative predictor of therapeutic
success. Sequential VL measurements with the same method
during treatment (at weeks 4, 12, 24/48) and 6 month after
treatment completion inform response-guided therapy (RGT).
Table 2.1 – Blood tests for hepatitis C
Test/Type Application Comments
EIA
(enzyme immunoassay)
Indicates past or present
infection
Does not differentiate
between acute and
chronic infection
All positive EIA results should be checked with a supplemental HCV RNA
assay:
HCV RNA qualitative
(RT-PCR)
Detects virus as early as 1-2
weeks after infection.
Useful for reduction of
residual risk associated to
transfusions*
Presence of circulating
HCV RNA might be
intermittent
A single negative RT-PCR is not conclusive
HCV RNA quantitative
(Real-time PCR)
Determines concentration
of HCV RNA (VL)
Useful for assessing the
response to therapy
HCV RNA genotyping Groups isolates of HCV
based on major genetic
types and subtypes
Determines the length
of treatment and
prediction of SVR rate
* screening by Versant™ (Siemens Health Care Diagnostics) and Procleix™ HIV-
1/HCV assays (Gen-Probe).
Determination of HCV genotype. The molecular
characterization of genotypes and subtypes of HCV is
particularly important for the response to treatment and disease
prognosis (Scott 2007). There are 6 major genotypes of HCV and
more than 50 subtypes.

No comments:

Post a Comment