To the core

Xchange newsletter - Autumn 2007

While three percent of the world’s population is thought to be infected with hepatitis C virus (HCV)¹, the majority of those infected remain undiagnosed. A positive test result would not only enable those patients to embark on a treatment regime, but may also encourage changes to potentially harmful patterns of behaviour that further spread the disease.

Recent estimates suggest that approximately 200,000 to 500,000 people are infected with HCV in England and Wales. In 2005, the Department of Health estimated that only 47,000 people with HCV infection had been diagnosed and only 7000 had been treated.²

HCV was first identified in the late 1980s and is one of five distinct viruses causing hepatitis (inflammation of the liver). A member of the Flaviviridae family, HCV is a small (<50 nm diameter), lipid-enveloped virus containing single, positive stranded RNA. The virus is highly variable with six recognised genotypes and many subgroups.³

HCV is readily transmitted by blood to blood contact. The risks posed by ordinary everyday contact with someone living with hepatitis C are very small (there is no evidence that hepatitis C is spread by sneezing, kissing, breathing in virus particles from the air, sharing cutlery etc) and a few practical guidelines reduce the risks further.⁴ Sexual transmission of HCV is a contentious issue as the risks are small and the route of transmission is not fully understood. It is believed that the risks increase with co-infection of HIV and if the person is acutely infected with the virus.

While acute infection is asymptomatic, 60-85% of those infected become chronically infected and, of those, 10-20% develop cirrhosis.

HCV detection

Definitive viral hepatitis detection for diagnostic or blood screening purposes requires a panel of viral-specific hepatitis tests. Using commercially available immunoassays, HCV antibodies may not be detected for 30-70 days after exposure. However, nucleic acid testing for detection of HCV RNA or HCV antigen testing for the detection HCV core protein has dramatically reduced this pre-seroconversion window period.

Now, Abbott has developed a highly sensitive assay for the quantitative determination of HCV core antigen for use on ARCHITECT immunoassay analysers. A poster presented at the Regional Congress of the ISBT- Europe⁵ determined assay sensitivity by testing 10 commercially available seroconversion panels that were initially nucleic acid negative. In each panel examined, a positive result in the HCV core antigen assay was obtained prior to detection of the HCV antibody, resulting in an average reduction in the window period of 35.8 days.

The poster continues to say that the ARCHITECT HCV core antigen assay was able to detect antigens in all of the panels on the same day as the nucleic acid test, thereby exhibiting equivalent sensitivity. The specificity of this assay was established at 99.78% by testing a population of normal volunteer US blood donors and hospitalised patients with medical conditions unrelated to HCV infection. The poster concludes that the HCV core antigen assay represents a viable alternative to nucleic acid testing for HCV diagnosis and for monitoring HCV therapy.

The Abbott HCV core antigen assay will soon be available.

www.clinicalevidence.com
NICE technology appraisal guidance 106, Peginterferon alfa and ribavirin for the treatment of mild chronic hepatitis C: Extension of the guidance given in NICE technology appraisal guidance 75; Nov 2007
www.gpnotebook.co.uk
www.haemaphilia.org.uk
Morota KX, Fujinami R, Kinukawa H, Aoyagi K, Iida K, Ishida T, Matsubara N, Machida T, Ohno K, Saegusa H, Maki N, Itoh T, Takeda K; A Fully Automated and Highly Sensitive Immunoassay for Hepatitis C Virus (HCV) Core Antigen; 2007