Background: Suppression of HIV viral load by HART to < 50 copies/mL has been shown to correlate with favorable clinical outcome. Thus viral load results reported as > 50 copies/mL in patients (pts) with previously undetectable RNA, have potential clinical and psychological impact. We investigated the distribution and analytic accuracy of results between 50 and 400 copies/mL for HIV-1 RNA quantitative assays performed by PCR or bDNA in pts previously reported as < 50 copies/mL across a large diagnostics reference laboratory system.

Methods: Clinical samples submitted for HIV RNA quantitative assays performed at three Quest Diagnostics reference laboratories were reviewed. Among more than 5,000 pt specimens assayed in Q2 and Q3, pts deemed by their HIV care providers as having unexpected low positives (blips) ranging from 50 copies to 1,000 had original and repeat blood-draw samples re-assayed at a second laboratory (Nichols Institute) to assess their analytic veracity.

Results: Of results, 12.9% were reported as between 50 and 200 copies/mL. An additional 8.4% were between 201 and 500 copies/mL. The distributions of results were not significantly different among the laboratories performing the assays, though fewer patients < 50 copies/mL were reported from the Southern USA with a corresponding increase in > 2,500. The variance of bDNA results was less that that of PCR and the distributions were different (p < 0.0001) with more < 50 by bDNA. But the proportion of pts with 50 to 400 copies/mL was the same by both assays. Clinically unexpected values (blips) were confirmed in 97% on the same specimen (within < 0.5 log copies/mL) and within < 0.75 log copies in 94% on a subsequent specimen.

Conclusions: Low positive HIV RNA results (blips) are common among pts under treatment and even when clinically unexpected are usually confirmed by repeat or subsequent assays using either PCR or bDNA. While bDNA results may vary less than PCR, rarely do blips appear to be due to analytic or laboratory variance. The clinical significance of these blips remains uncertain.