Viral load refers to the amount of hepatitis C virus (HCV RNA) present in a person's blood.  Viral levels as measured by HCV RNA do not correlate with the severity of the hepatitis or with a poor prognosis (as in HIV infection).

Rates of response to interferon therapy are higher in patients with low levels of HCV RNA. There are several definitions of a "low level" of HCV RNA, but the usual definition is below 1 million IU (2 million copies) per mL.

However, there is no level of HCV RNA that absolutely precludes the possibility of a response and there is little or no correlation between disease severity or disease progression and level or titer of HCV RNA.

While testing may be useful in making an initial diagnosis, repeatedly testing an untreated patient over time is not helpful, because almost all patients continue to have detectable levels of virus. 

In untreated patients, an undetectable or negative result may merely reflect a temporary fall of virus levels below the level of detection rather than permanent clearance.

On the other hand, repeat testing for HCV RNA during interferon therapy can be helpful, because loss of HCV RNA with treatment is a strong predictor of a sustained beneficial response.

Variation in Test Results

These testing methods are not standardized, and different methods by different laboratories can provide different results on the same specimen. It’s important that your physician use the same laboratory for viral load testing each time to be sure that the results from different tests can be compared to each other.

What units are used to reports measures of viral load?

• Viral load can be reported as a raw number, such as 6,200,000 copies per mL
  
  
• Viral load can be reported in millions, such as 6.2 million copies per mL
  
  
• Viral load can be reported as an exponent, so that 6.2 x 10⁶ means 6,200,000.

Sometimes instead of reporting the actual number of viral copies, labs will report viral load in IU or International Units.  The International Unit was developed by the World Health Organization in an effort to standardize the values obtained for HCV viral load monitoring between various testing methods.

Unfortunately, one viral copy is not the same as one IU, and different tests use various ratios to convert from viral copies to IU's.

For example, Quest Diagnostics uses these formulas to convert one unit to another:

• In tests using Polymerase Chain Reaction (PCR) technology: Copies/mL = IU/mL x 2.7
  
  
• In tests using Branched DNA  (bDNA) technology: IU/mL = Copies/mL x 5.2
  
  
• In tests using Transcription-Mediated Amplification (TMA) technology: Copies/mL = IU/mL x 5.2

Qualitative Hepatitis C Viral Assays

A qualitative test will either give a positive or negative result (sometimes called reactive or nonreactive). This tells the patient that the virus either is, or is not present, but does not indicate how much virus is present.