Hep C Discussion Forum

Hi all,

We have recently had some confusion about Viral Load (VL) results. This is a complex subject and outside specialist HIV/Hepatology Clinics, it is not surprising that Nurses and NP's have trouble relaying correct information.

Knowing your VL is essential to diagnose active HCV, and particularly in assessing your response to treatment.

There are several different companies that market VL Test Kits. These vary from country to country and there are often several versions of each kit, with the latest version being the most accurate and reliable. The major players are Roche, Abbott, Labcorp and Quest. By far the most common is the Roche PCR assay and this is used worldwide. Forum members have posted results using at least 3 of the Roche versions. The latest version goes by the name of : COBAS Ampliprep/COBAS TaqMan HCV assay- vers.2

Whatever test you are using, it will give a Lower Limit of Detection (LLOD). For the above Roche test, this is 15 i.u./ml

In the USA, a 2 stage test is available from Quest (Heptimax) and Labcorp (Quantasure). These use the normal Roche PCR assay, and if undetectable at the LLOD, they use TMA (Transcription Modified Amplification) to measure down to LLOD of 5 and 2 i.u./ml. They are expensive!

All of the PCR tests use a synthetic copy of a small, stable portion of the HCV genome. This is common to all Genotypes and all viral mutations, and is called the 'target'. Your blood is compared with a huge number of dilutions of 'target' until a match is found. Each dilution is equivalent to a known VL.

Reporting a VL result has it's own problems. For years, Pathologists have been trying to standardise reporting, using i.u./ml (where an i.u. is equivalent to about 2.5 viral particles). Companies can't even agree on how many viral particles should equal 1 i.u. At least most Labs are now reporting in whole numbers, and giving their LLOD.  Some Canadian Labs still use the old Scientific Notation The result will have an E in it eg. a VL 2,140,000 i.u./ml = 2.14E + 6   Others persist in using Log Units eg. a VL of 1 million = 6 log units. This can cause great confusion when relayed over the telephone to a patient, so it is why it is essential to get a copy of the VL report.

Detected or Undetected: Some Labs make a mess of reporting this, causing confusion for patients and doctors. In patients with a detectable whole number, this is not a problem. Too often the report merely says  <50 , or <25  or <15. If the report continues ' 'detected but not quantifiable', or ' Target Detected', this is clear. If the report continues 'Undetected' or 'Target not Detected or TND' this also is clear. If there is no qualification, the report is assumed to be Detected. To be accepted as an Undetected result, the Lab report MUST say Undetected  or TND.

Patients need to understand this is not straightforward. Please try to get a copy of your report.