Hepatitis C Antibody and RNA

Hepatitis C virus (HCV) is an RNA virus transmitted by blood. The anti-HCV antibody immunoassay is the screening test, indicating exposure at any time.

A reactive result is followed by HCV RNA (quantitative or qualitative PCR), which shows active infection. HCV core antigen is an alternative to RNA.

HCV genotype was used to select treatment but modern pangenotypic direct acting antivirals (DAAs) have made it less necessary. Fibrosis staging by elastography or serum scores, and sustained virological response (SVR) 12 weeks after treatment, complete the assessment.

About 58 million people have chronic hepatitis C, with 1.5 million new infections and 290 000 deaths a year, mainly from cirrhosis and liver cancer. About 70% of acute infections become chronic. Chronic infection leads to cirrhosis in 15 to 30% over 20 to 30 years. DAAs cure over 95% of patients in 8 to 12 weeks, making hepatitis C a curable disease, and elimination is possible only if people are tested.

Indications. Everyone aged 18 years or over once (universal screening), people who inject or have injected drugs, recipients of blood or organs before screening was introduced (before 1992 in many countries), dialysis patients, people with HIV, children of infected mothers, unexplained raised ALT, healthcare workers after needle stick, prisoners, men who have sex with men with risk factors, tattoos or piercings with unsterile equipment, and pregnant women in some programmes.

Specimen. Serum or plasma, 3 to 5 mL. Stable at 2 to 8 °C for several days. For RNA, plasma separated within 6 hours or serum, kept at 2 to 8 °C, and frozen for transport beyond 72 hours. Dried blood spots and point-of-care RNA tests extend access.

Algorithm.

• Anti-HCV non-reactive: no infection, unless exposure within 3 to 6 months (window period of 4 to 10 weeks with third generation assays), immunosuppression or acute infection, when RNA is tested.
• Anti-HCV reactive: reflex HCV RNA (or core antigen).
• RNA detected: current infection. Offer treatment.
• RNA not detected: resolved infection (spontaneous clearance in 20 to 30% of infections, or cure after treatment), or false positive antibody. Repeat RNA if recent exposure suspected.
• Antibody remains positive for life after clearance and does not protect against reinfection.

HCV RNA. Reported in IU/mL (log10). The level does not predict severity or disease progression, but it is used to confirm infection and to assess response. Detectable RNA at 4 weeks of treatment is not used to alter therapy with modern DAAs. Test of cure is HCV RNA undetectable at 12 weeks after completing treatment (SVR12).

Genotype. Genotypes 1 to 7 and subtypes: genotype 1 is the commonest worldwide (about 46%), genotype 3 (30%) is associated with steatosis and faster fibrosis, genotype 4 is common in Africa and the Middle East, genotype 5 in South Africa and genotype 6 in South-East Asia. Pangenotypic regimens (sofosbuvir with velpatasvir, glecaprevir with pibrentasvir) cure all genotypes in 8 to 12 weeks, with genotype testing optional.

Fibrosis staging. Transient elastography (FibroScan: under 7 kPa excludes significant fibrosis, over 12.5 kPa suggests cirrhosis), FIB-4 (under 1.45 low risk, over 3.25 advanced fibrosis), and APRI (over 1.0 suggests cirrhosis). Cirrhosis changes the choice of drugs and duration, and requires liver cancer surveillance for life.

Acute hepatitis C. Anti-HCV may be negative for up to 8 to 12 weeks, so HCV RNA is needed within the first weeks. Spontaneous clearance occurs in 20 to 50%, and treatment is started if RNA persists beyond 12 weeks (or earlier in high risk groups).

Drug interaction and resistance testing. Before treatment: interactions with other drugs (amiodarone with sofosbuvir risk bradycardia, proton pump inhibitors reduce velpatasvir absorption, anticonvulsants and rifampicin reduce DAA levels). Resistance testing is considered after DAA failure.

Critical values and findings needing immediate action.

• Positive RNA with decompensated cirrhosis (ascites, jaundice, encephalopathy, variceal bleeding): referral to a specialist centre, treatment with a protease inhibitor free regimen, and transplant assessment.
• Hepatitis B coinfection (HBsAg or anti-HBc positive) before DAAs: monitoring or prophylaxis, since reactivation with liver failure can occur.
• Needle stick exposure: baseline testing and RNA at 3 to 6 weeks, with treatment if infection develops.
• Positive RNA in a pregnant woman: DAAs are deferred until after delivery, and the infant is tested at 18 months (antibody) or earlier by RNA.
• Liver failure with a positive RNA and hepatic encephalopathy: urgent assessment.

Interferences and pitfalls.

• A positive antibody alone does not mean current infection. RNA must always follow.
• False positive antibody results are more frequent in low prevalence populations (blood donors, pregnant women) and in autoimmune disease.
• False negative antibody results occur in the window period, in immunocompromised patients (HIV, transplant, haemodialysis) and in agammaglobulinaemia. RNA is used for these patients.
• RNA can be intermittently undetectable in acute infection or in early chronic infection, and repeat testing is done if suspicion remains.
• HCV core antigen is less sensitive than RNA (detects over 3000 IU/mL).
• After SVR12, reinfection occurs in people with ongoing risk (people who inject drugs, men who have sex with men) at 1 to 6% a year, and RNA testing is repeated annually in them.
• Normal ALT does not exclude fibrosis.
• Cure does not remove the need for liver cancer surveillance in patients with cirrhosis.
• Treatment failure is uncommon (under 5%) and associated with advanced liver disease, prior treatment, and non-adherence.

Special groups.

• Pregnancy: screening is offered in many programmes, and transmission to infants is about 5% (higher with HIV).
• Children: DAAs are approved from 3 years, and infants are tested after 18 months.
• People who inject drugs: treatment is effective and does not require abstinence, with testing and treatment at harm reduction services.
• Kidney disease and dialysis: pangenotypic DAAs are safe, and HCV-positive organs can be used for transplant.
• HIV coinfection: faster fibrosis progression, and drug interactions with antiretrovirals are checked.
• Regions: Egypt, Pakistan and Central Asia have high prevalence, and unsafe injections and blood transfusions remain sources, and low cost generic DAAs and point-of-care RNA expand access.

Follow up tests. HCV RNA, ALT and AST, liver function and INR, full blood count and platelets, FibroScan or FIB-4, hepatitis B serology, HIV test, ultrasound and alpha fetoprotein every 6 months in cirrhosis, creatinine and eGFR, drug interaction review, HCV RNA at 12 weeks after treatment, and annual RNA in people with ongoing risk.