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Several blood tests, outlined below, can determine whether a patient has been infected with HCV. Often, a patient will need to undergo more than one of these tests to confirm an HCV diagnosis.
When a person is infected with a virus, the body responds by producing antibodies specific to that virus. The presence of HCV antibodies means that the person has been exposed to HCV at some point, although the body may have cleared (eradicated) the virus. However, as only 10 to 50 per cent of those infected are able to clear the virus themselves,1 HCV infection should be confirmed using other tests.2
HCV RNA Tests
This blood test can find genetic material (RNA) unique to HCV that indicates infection. HCV RNA can be detected in the blood for up to 2 weeks after exposure to the virus. Genotype testing is an additional component of the HCV RNA test. Genotyping may be important in determining treatment options and also in predicting how the virus will respond to therapy.
There are two types of HCV RNA tests:
Liver Biopsy
If hepatitis C is diagnosed, a liver biopsy can be used to grade the severity of liver damage as well as rule out other causes of liver disease (such as alcohol or iron overload). A small sample of liver is removed and then assessed under the microscope.
Non invasives alternative methods to evaluate the severity of liver damage methods use biochemical parameters to calculate the fibrosis score (e.g. Fibrotest, Fibrometer, Forns, APRI, Sud, Leroy, ELF, Fibrospect) or measure the stiffness of the liver in vivo (e.g. Fibroscan, Echosens, France)
The combination of fibroscan plus fibrotest may help avoid a liver biopsy in many patients.
Raised Liver Enzymes
Levels of the liver enzyme ALT are often measured as part of a routine blood test. Raised ALT levels are a sign of liver inflammation and therefore viral hepatitis C and B has to be excluded if ALT levels are elevated.
New research has revealed that approximately 80 per cent of people with ‘normal’ ALT levels have some level of liver damage and up to 25 per cent have seriously damaged livers.3 Hence patients with 'normal' ALT should not be excluded from treatment with PEGASYS, the only approved drug for the treatment of 'normal' ALT patients.
Molecular assays such as the AMPLICOR and COBAS AMPLICOR HCV MONITOR® tests, as well as the recently introduced High Pure/COBAS TaqMan HCV Test, are used to determine baseline viral load and changes in viral load during treatment (eg week 12). A qualitative test should be utilised, such as the AMPLICOR or COBAS AMPLICOR HCV Tests, v2.0, to confirm infection and assess outcome of therapy.
The AMPLICOR HCV MONITOR® Test, v2.0 is the industry standard test used to quantify viral load and monitor patients’ response on therapy. However, the next generation COBAS TaqMan HCV Test provides up to a 7 log linear range for an accurate viral load determination throughout the clinically-relevant range of HCV infection. The outcome of therapy is related to the HCV RNA levels prior to treatment; high baseline viral loads resulting in lower rates of sustained viral response (Davis and Lau, 1997; Martinot-Peignoux et al, 2000). The qualitative AMPLICOR and COBAS AMPLICOR HCV tests, with a lower limit of detection of 50 IU/mL can be used to determine whether treatment has resulted in a sustained viral response.
The High Pure/COBAS TaqMan HCV Test, recently developed by Roche for the quantitative determination of HCV RNA levels, offers automated, closed-tube amplification and detection, minimising potential testing errors due to user intervention and contamination. It enables optimal monitoring of treatment success and early detection of treatment failure through enhanced sensitivity, specificity and broad linear range.
Liver biopsies are often used to support diagnosis, assess disease severity (necroinflammation and fibrosis) and assess therapeutic effectiveness (Perrillo, 1997; Brunt, 2000; Saadeh et al, 2001). Recent consensus treatment guidelines have moved away from recommending biopsy in all patients prior to initiating therapy (French Consensus Conference Statement: Treatment of Hepatitis C, 2002; National Institutes of Health Consensus Statement, 2002).
Prior to the introduction of HCV RNA tests, serum alanine aminotransferase (ALT) measurements were often used to assess responses to therapy. However, ALT is an unreliable marker of liver damage since the absolute measure of serum ALT does not correlate with the degree of severity of liver disease (Kaplan, 2002). Although very high ALT levels are generally associated with hepatocellular damage and can, in many instances, provide an indication of underlying disease, low levels of ALT are not always associated with mild liver disease and ALT levels tend to drop in advanced cirrhosis. As biochemical responses do not always correlate well with the virological response (Marcellin et al, 1999; 2001), viral RNA determination is now considered the ‘gold standard’ for monitoring on-treatment response to pegylated IFNα therapy.
References:
1. Micallef JM, Kaldor JM, Dore GJ. Spontaneous viral clearance following acute hepatitis C infection: a systematic review of longitudinal studies. J Viral Hepat 2006; 13(1):34-41.
2. National Institutes of Health Consensus Development Conference Statement: Management of hepatitis C; June 10-12, 2002. Hepatology 2002;36 (5 Suppl 1):S3-20.
3. Puoti C, Castellacci R, Montagnese F, et al. Histological and virological features and follow-up of hepatitis C virus carriers with normal aminotransferase levels: the Italian prospective study of the asymptomatic C carriers (ISACC). J Hepatol 2002;37(1):117-23.