Hepatitis C is a viral infection that primarily affects the liver. For many, the first indication of a potential issue comes from a blood test ordered by a healthcare provider. Receiving a laboratory report can be confusing, especially when it contains specific values and ratios. Understanding the purpose of this initial test is the first step in making sense of your results and figuring out what comes next.
Understanding the HCV Antibody Test
The initial screening for Hepatitis C virus (HCV) is an antibody test. Your immune system produces antibodies when it encounters a foreign invader, such as a virus. These proteins are tailored to recognize and fight that specific threat. The HCV antibody test does not look for the virus itself; instead, it searches for the specific antibodies your body would have made if it was ever exposed to the Hepatitis C virus.
These tests are often semi-quantitative, meaning they measure the amount of antibody present and report it as a signal-to-cutoff (S/CO) ratio. The “signal” (S) represents the quantity of HCV antibodies detected in your blood sample. This measurement is then compared against a “cut-off” (CO), which is a predetermined threshold value established by the laboratory for that specific test.
The lab calculates your S/CO ratio by dividing the signal value by the cut-off value. A result is considered “reactive” if the ratio is 1.0 or greater, and “non-reactive” if it is less than 1.0.
Interpreting Your S/CO Ratio Result
A non-reactive result, with a ratio below 1.0, indicates that no HCV antibodies were found in your blood. For most people, this means they have not been exposed to the Hepatitis C virus, and no further testing is required.
A reactive result, with an S/CO ratio of 1.0 or higher, means that HCV antibodies were detected. This indicates that you have been exposed to the virus at some point in your life. A reactive result does not, by itself, confirm a current, active infection. The body can sometimes clear the virus on its own, but the antibodies will remain, much like a memory of the past infection.
The S/CO ratio is not a measure of how sick you are. A person with a high ratio, such as 46.0, is not necessarily more ill or carrying more of the virus than someone with a low reactive ratio, like 1.5. The purpose of this ratio in a screening context is to provide a positive or negative result for the presence of antibodies.
Distinguishing Between Screening and Confirmatory Tests
The HCV antibody test is a screening tool, not a final diagnosis. A reactive result indicates that a second, different type of test is needed to determine your actual infection status. This is because the presence of antibodies can mean you either have a current, active infection, or you had a past infection that your body’s immune system successfully eliminated.
To distinguish between these two possibilities, healthcare providers use a confirmatory test known as an HCV RNA test. This test is often referred to as a Polymerase Chain Reaction (PCR) or viral load test. The difference lies in what each test detects. The antibody test looks for the immune system’s response to the virus. In contrast, the HCV RNA test directly detects the genetic material (ribonucleic acid, or RNA) of the Hepatitis C virus itself. If the virus’s RNA is present in your bloodstream, it confirms an active infection.
Follow-Up Steps After a Reactive Result
Receiving a reactive antibody test result means your next step is to schedule a follow-up appointment with your healthcare provider. This discussion is to arrange for the confirmatory HCV RNA test. This second test determines if the virus is currently active in your body.
If the RNA test is positive, it confirms a current, or chronic, HCV infection. This diagnosis will prompt a more detailed conversation with your doctor about assessing your liver health and exploring treatment options.
If the HCV RNA test comes back negative or “not detected,” it means there is no active virus in your bloodstream. This outcome suggests one of two scenarios: either the initial antibody test was a false positive, or you were infected with HCV in the past and your immune system cleared the virus without any medical intervention. Your doctor will likely conclude that you do not have a current Hepatitis C infection.