Resolving a diagnosis for people with persistently indeterminate HIV test results

Simon Collins, HIV i-Base

A poster from the UK outlined an important practical way to resolve HIV diagnoses for the small minority of people who persistently have indeterminate results.

This study was presented by Colin Brown from Public Health England, with colleagues from the Royal Free and Imperial College and included 14 cases when HIV tests showed low-level or indeterminate antibodies and negative results to standard HIV RNA/DNA testing.

All participants provided a larger blood sample (60 mL) that was divided equally between a clinical, academic, and public health laboratory, and immediately processed.

Despite all samples testing RNA negative using a 20 copy/mL cut-off, molecular testing using a single copy viral load test amplified HIV RNA in 8/14 cases and was DNA positive in another 2/14. Western blot results (not routinely used in the UK) showed 11/14 positive to p24 and 12/14 positive to gp160. Use of CD4, CD8 and ratio were not helpful in showing any unexpected results.

These more sensitive tests were able to confirm 11/14 diagnoses, refute 1 diagnosis, with only 2/14 left unresolved.

One of these individuals on PEP converted to ART on diagnosis and one developed high-level viral load.

This study confirmed that western blot is an essential test for indeterminate results and commented that such cases might become more common in the context of wider use of PrEP, where the decision to change to early ART might be particularly important.


Brown C et al. Adapting HIV testing algorithms and clinical advice for people with persistently indeterminate test results – a novel national referral clinical service. AIDS 2018, 23-27 July 2018, Amsterdam. Poster TUPEB038. (abstract and poster)

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