Hepatitis C Antibody (Anti-HCV)

A reactive (positive) anti-HCV result usually means the immune system has met hepatitis C at some point, though some reactive results are false positives. One more test, HCV RNA, says whether the virus is in your blood today. Many people with a positive antibody have no current infection: about 30 percent of people infected with hepatitis C (range 15 to 45 percent) clear the virus within about 6 months without treatment, and the antibody stays behind after the virus is gone ⁵.

What the anti-HCV test measures

The anti-HCV test looks for antibodies, the proteins your immune system makes after it meets the hepatitis C virus (HCV). For how antibody and antigen tests differ across viruses, see viral serology explained. Antibodies are a record of contact. They tell you the immune system has seen the virus, and they say nothing on their own about whether the virus is still there.

For hepatitis C, the usual "is it there now" test is HCV RNA rather than an antigen test. CDC's testing guidance spells out the three things a reactive anti-HCV result can mean ¹:

A reactive result indicates one of the following: 1) current HCV infection, 2) past HCV infection that has resolved, or 3) biologic false positivity for HCV antibody.CDC, Testing for HCV Infection: An Update of Guidance for Clinicians and Laboratorians, MMWR 2013 ¹

A biologic false positive is an antibody result that reads positive in someone who never had hepatitis C. False positives are more common where few people carry the virus. That is one reason a reactive antibody result goes on to an RNA test; the main reason is that the antibody cannot tell a current infection from a past one. CDC recommends following every reactive antibody result with a confirming RNA test ¹.

Why a positive antibody is followed by an HCV RNA test

HCV RNA testing, also called a nucleic acid test (NAT) or viral load test, looks for the genetic material of the virus itself. If HCV RNA is in the blood, the virus is present and replicating. CDC recommends that every reactive anti-HCV result be followed by an HCV RNA test ¹.

The four result combinations

The first three rows follow the CDC interpretation guidance; the fourth comes from CDC's guidance on recent exposure ¹. People with a weakened immune system, for example on dialysis, can also test antibody-negative with a current infection, so their clinician may order RNA directly ¹⁴.

If a clinician wants to separate a cleared infection from a false positive in the third row, CDC notes that a second, different antibody test can do it ¹. For most people the distinction changes nothing, because in both cases no virus is present now.

Reading the anti-HCV result on your report

Most labs report anti-HCV as reactive or nonreactive (sometimes positive or negative). Some reports also print a number, often called a signal-to-cutoff ratio or index, which compares the strength of the antibody signal with the lab's cutoff. The number does not settle the question. Any reactive anti-HCV result, weak or strong, goes on to an HCV RNA test ¹.

For a wider guide to the flags, units and ranges on a lab report, see how to read any lab result.

Timing: why an early antibody test can miss a new infection

After someone is infected with hepatitis C, HCV RNA becomes detectable in the blood within 1 to 2 weeks, while anti-HCV usually takes 8 to 11 weeks and sometimes longer ⁶. That gap is the antibody test's window period. A nonreactive anti-HCV test a few weeks after a possible exposure does not rule out hepatitis C.

Who should be tested, and how often

• All adults aged 18 and older, at least once in a lifetime (CDC). The only exception is places where fewer than 1 in 1,000 people (0.1 percent) have the virus ².
• Every pregnant person, during each pregnancy, with the same 0.1 percent exception (CDC) ².
• All adults aged 18 to 79, at least once (US Preventive Services Task Force, USPSTF, the US expert panel on preventive care; its grade B means it recommends the test based on evidence of clear benefit) ³.
• People with ongoing risk, such as people who currently inject drugs, tested periodically while the risk continues (CDC) ².
• Anyone who asks for the test, regardless of reported risk (CDC) ².

Hepatitis C screening at least once in a lifetime for all adults aged ≥18 years, except in settings where the prevalence of HCV infection (HCV RNA-positivity) is <0.1%.Schillie S et al., CDC Recommendations for Hepatitis C Screening Among Adults, MMWR Recomm Rep 2020 ²

In plain terms: every adult should be tested at least once.

How the test is done

Anti-HCV is a standard blood draw from a vein, and no fasting is needed. Labs often order it together with hepatitis B tests such as HBsAg, anti-HBc and anti-HBs, and an HIV Ag/Ab combo test. Many labs now run HCV RNA automatically on the same sample when the antibody is reactive, a practice called reflex testing, which saves a second visit.

Because USPSTF gives hepatitis C screening a grade B ³, the Affordable Care Act requires most non-grandfathered private US health plans to cover the screening test as preventive care without cost sharing. Coverage varies, so check your plan, including for the follow-up RNA test.

After treatment: why the antibody stays positive

Hepatitis C treatment today uses direct-acting antivirals (DAAs), tablets that block the virus from copying itself. Most people take them for 8 to 12 weeks, and more than 95 percent of people who complete treatment are cured ⁴. Cure is measured as sustained virologic response (SVR): HCV RNA still undetectable 12 weeks after the last dose ⁴.

Anti-HCV usually stays positive for life after hepatitis C clears, whether it cleared on its own or with treatment ¹⁴. A repeat antibody test after cure will read reactive, which is expected and does not mean the treatment failed. Clearing hepatitis C does not protect against catching it again, so anyone with a new possible exposure after cure is checked with HCV RNA rather than the antibody test ⁴.

How anti-HCV fits with your liver enzymes

Hepatitis C inflames the liver over years, and that can raise the liver enzymes ALT and AST. A normal ALT does not rule out hepatitis C, because many people with chronic infection have normal or only mildly raised enzymes ⁴. A raised ALT has many other causes, such as fatty liver. For what ALT and AST patterns mean, see liver enzymes explained.

More on the liver and on infection testing: the liver topic hub and the infections topic hub.

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