There are two main types of HCV viral load tests:
Qualitative viral load tests determine the presence of HCV RNA (genetic code) in the blood. This type of test is usually used to confirm chronic infection with HCV. If viral RNA is detected, a
positive result is reported. If viral RNA is not detected, the test result is negative.
Up to 15% of people infected with HCV clear the infection without treatment. These people have a positive antibody test and a negative viral load test.
Quantitative viral load tests measure the amount of virus in one milliliter of blood. They are often used to assess whether or not treatment with interferon or interferon plus ribavirin is likely to be
successful and, later, if treatment is working.
There are different techniques for counting HCV virus:
Different tests can give different results for the same sample. Because the tests are different, you should use the same kind of test to measure your viral load over time.
Viral loads are usually reported as copies of virus in one milliliter (mL) of blood. However, because the different test technologies gave different viral load results, HCV viral loads are reported as International Units (IU) per mL
The best viral load test result is “undetectable.” This is not a guarantee that there is no virus in your blood; it might mean that there is not enough for the test to find and count. Viral loads below 800,000 IU/mL are considered low; above 800,000 are considered high.
HCV is physically much smaller than HIV and it multiplies much faster. HCV viral loads can be in the millions. But with successful treatment, HCV can be cured.
Viral load changes are often described as “log” changes. This refers to scientific notation, which uses powers of 10. For example, a 2-log drop is a drop of 102 or 100 times. A drop from 600,000 to 6,000 would be a 2-log drop.
The viral load is helpful in several areas:
There are several viral load measures of treatment response. These are described below.
HCV viral load cannot be used the same way as the HIV viral load (see fact sheet 125).
It is not a good indicator of how serious the hepatitis is, or how fast it will progress. It is also more complicated to use in evaluating response to treatment.
in the past, lower viral loads are associated with better response to HCV therapy, but this is no longer the case with modern HCV drugs. Also, higher viral loads are linked to higher risk of transmission of HCV, at least from pregnant mothers to their newborns.
There are several types of HCV viral load response to treatment: ETR (end-of-treatment response):
This means having an undetectable HCV viral load at the end of HCV treatment.