HIV antigen–antibody combination enzyme immunoassay—the experience of a London Teaching Hospital

✍ Scribed by Simon Goldenberg; Ranjababu Kulasegaram; Barry Peters; George Panayotakopoulos; C.Y. William Tong

• Publisher: John Wiley and Sons
• Year: 2007
• Tongue: English
• Weight: 105 KB
• Volume: 79
• Category: Article
• ISSN: 0146-6615
• DOI: 10.1002/jmv.20964

✦ Synopsis

The introduction of the fourth generation HIV antigen-antibody combination enzyme immunoassay (HIV Ag-Ab EIA) has led to a reduction in the diagnostic ''window period'' when HIV antibody is negative during primary infection. This facilitates earlier laboratory diagnosis during sero-conversion. An HIV Ag-Ab EIA (AxSYM, Abbott Laboratories, Kent, UK) was introduced to a London Teaching Hospital since 2004 as the primary screening test. Confirmation was performed using another HIV Ag-Ab EIA (Vironostika, BioMe ´rieux, Hampshire, UK) and an HIV Ab only assay (Bispot, Orgenics, Yavne, Israel). Retrospective analysis identified a total of 20 sero-converting patients who would have been missed if the standard antibody-only HIV tests had been used as the primary screening test. This accounted for approximately 3% of the new diagnoses made by the laboratory. The median time from onset of illness to sero-conversion was 18 days. Two patients had multiple samples analyzed between initial presentation and eventual sero-conversion. One had a prolonged seroconversion illness lasting for over 137 days; the other sero-converted within 17 days. A plotting of the signal to cut-off ratio with time of the two HIV Ag-Ab EIAs showed a V-shaped curve and both tests were below cut-off at some time-points during sero-conversion. These two cases highlighted the difficulties in diagnosing HIV infection during sero-conversion. On the basis of these results, it is recommended that a fourth generation HIV Ag-Ab EIA could be considered for use as the standard of care, particularly in any population with a high rate of HIV infection.