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Updated: Jun 26, 2026
Pairwise Growth Competition Assay for Determining the Replication Fitness of Human Immunodeficiency Viruses
Published on: May 4, 2015
An international collaborative study to establish a replacement World Health Organization International Standard for
1Divisions of Retrovirology, National Institute for Biological Standards and Control, Blanche Lane, South Mimms, Potters Bar, Hertfordshire, UK.
Background And Objectives:
An international collaborative study was undertaken to identify a replacement for the World Health Organization (WHO) 1st International Standard for human immunodeficiency virus 1 (HIV-1) RNA for use in nucleic acid-based techniques (NAT) (code 97/656). In the original study to establish the 1st International Standard, a second candidate material (code 97/650) had been shown to perform well and this was re-evaluated to establish whether it would be a suitable replacement.
Materials And Methods:
Eight laboratories from six different countries participated in the collaborative study to evaluate the candidate replacement standard. A total of eight different NATs were used, five in a quantitative format and three qualitative, of which five were commercially available.
Results:
The results showed that the estimates of RNA copies in the current study were generally in line with those of the original study and there was no evidence of any drift in overall levels expressed in International Units (IU) for the candidate standard between the two studies. Furthermore, it was shown to be stable over long-term storage at -20 degrees C.
Conclusions:
The candidate material code 97/650 was established by the WHO as the 2nd International Standard for HIV-1 RNA for use in NAT and assigned a unitage of 5.56 log(10) (363 078) IU/vial.
