Validation and standardisation of nucleic acid amplification technology (NAT) assays for the detection of viral contamination of blood and blood products.

Standardisation of NAT assays is necessary before the introduction of such assays for routine screening of blood and blood products for viral contaminants such as HBV, HCV, and HIV-1. Standardisation can be achieved by the use of well-characterised reference materials (working reagents) to validate each assay run. Working reagents for HCV, HIV-1, HBV, HAV, and human parvovirus B19 have been established by the NIBSC. Such reagents and reference panels are also available from other official medicinal control laboratories and commercial organisations. However, the nucleic acid content of these reagents are expressed in many different units, e. g. genome equivalents/ml, copies/ml, PCR detectable units/ml, making comparisons of results from laboratories using different reagents difficult. The establishment of internationally accepted standards against which all working reagents could be calibrated, using a common standard unit of measurement, IU, would overcome this major problem. The first International Standard for HCV RNA assays was established in 1997. This reagent, 96/790, is a lyophilised preparation of a genotype 1 isolate and the concentration of the standard is 10(5) IU/ml. Two further International Standards have since been established; for HIV-1 and HBV, containing 10(5) IU/ml and 10(6) IU/ml respectively. The establishment of the HCV International Standard has been critical in the introduction of mandatory testing. Since 1st July 1999, all batches of blood products marketed in Europe have to be prepared from plasma pools tested and found non-reactive for HCV RNA using a validated assay which can detect a sample containing 100 IU/ml of HCV RNA. In Germany, screening of blood donations for HCV RNA by NAT has been mandatory since 1st April 1999. The minimum sensitivity of assays should be 5000 IU/ml for a single donation.