Question 1. Why are HCV results being reported in IU/mL? What is log IU/mL?

IU/mL is the abbreviation for international units per milliliter. Results are reported in IU/mL units to facilitate comparisons between results generated by available test methods. This is important because the various methods are not standardized. Use of IU/mL helps standardize viral load test results.

We also report the viral load in log IU/mL units. PCR test results on the same sample can vary as much as 0.5 log IU/mL; thus, only changes greater than 0.5 log IU/mL are clinically significant.

Reporting the viral load in log IU/mL units helps the doctor accurately interpret changes in viral load and better assess a patient's response to treatment.

Question 2. What do these test results mean: “<43 Detected” or “<43 Not Detected”?

According to the reagent manufacturer, the lower limit of detection differs from the limit of quantification. The lowest viral load this assay can accurately quantify is 43 IU/mL, but the limit of detection is 7.1 IU/mL for genotype 1 viruses, and 10 IU/mL for viruses with all other genotypes. Therefore, we can qualitatively report detection even if the viral load is under 43 IU/mL (ie, <43 Detected). Thus, “<43 Detected” means the assay was able to detect HCV RNA but was not able to accurately quantitate the viral load (ie, RNA >7.1 or >10 IU/mL, but <43 IU/mL). A “<43 Not Detected” means the assay did not detect HCV RNA (ie, RNA <7.1 or <10 IU/mL). This is compliant with the package insert guidelines for the new direct-acting antivirals boceprevir and telaprevir.

If a quantitation below 43 IU/mL is desired, please order the Heptimax^®HCV RNA test. This test provides our broadest analytical measurement range. By combining real-time PCR and transcription mediated amplification (TMA) technology into a progressive test, we can report a viral load range between 5 and 69,000,000 IU/mL. This is the most sensitive HCV RNA test available.