Hepatitis C (HCV) and Viral Load
Am I Getting Sicker if My Viral Load Is Rising?
Dr. Anania: Not necessarily. With HCV, viral burden in hepatitis C does not necessarily predict the natural history of clinical disease. And therefore, patients need to understand that we use that measurement to help us guide therapy and response to therapy. We use it in conjunction with other types of laboratory data -- liver enzymes, liver biopsies sometimes, and viral genotype. Taken all together, these tests give us a snapshot of what is going on. But viral load numbers themselves do not predict disease.
Dr. Pearlman: Unlike HIV, HCV viral copies do not directly affect a patient's prognosis and how fast disease is progressing in the liver. Remember, we are measuring blood levels, not what is happening in liver cells. HIV viral load does have a lot to do with quicker progression to AIDS. But HCV viral load does not tell you how fast hepatitis is progressing.
Does a Drop in Viral Load Mean Treatment Is Working?
Dr. Pearlman: We often talk about viral load numbers, but we really look at this in terms of logarithms. A "1 log" change is a 10-fold difference. Significant changes in viral load are a 2-log difference or a 100-fold change. This can be deceptive. If you have a viral load of 800,000 and it drops to 400,000, that seems like a big drop. But it's only changed by a factor of two. A change from 800,000 to 8,000 would be significant. This is important when we look at response to treatment. Twelve weeks after starting treatment, we see if a person's viral load has dropped 2 logs or more from baseline. If it has not, we are almost sure the treatment is not going to work.
How Long Must a Viral Load Be Undetectable Before Someone Is "Cured?"
Dr. Anania: Generally we like to see six months of continued undetectable viral load after treatment to say a patient's virus is in remission. I cannot say they are "cured."
Dr. Pearlman: After treatment, [patients] have a "sustained virologic response" or SVR. That is defined as undetectable viral load by PCR to under 50 IU/mL for 24 weeks after treatment is completed. If that is the case, that is an SVR. SVR means it's 98% certain you are cured. But there are very rare cases where people relapse if you check their viral load a year or two out. But it doesn't mean you can't get hepatitis C again if you engage in high-risk behaviors.