666 Comparative Performance of Two Viral Load Commercial Assays on HIV Subtype B and C B. Gotesman1, Z. Grossman2, M. Lorber3, I. Levi2, P. Shitrit1, F. Mileguir2, M. Y. Chowers*1 1Meir Med Ctr, Kfar Saba, Israel; 2Chaim Sheba Med Ctr, Tel Hashomer, Israel; and 3Rambam Med Ctr, Haifa, Israel
Background: The largest percentage of new HIV infections in the year 2000 was due to subtype C, while subtype B accounted for only 12% of infections. Non-B subtype infections are increasing in numbers not only in the developing world, but in Europe as well. In Israel, a large percentage of the patient (pt) population is from Ethiopia, and is infected with HIV subtype C. During routine monitoring of viral load with NucliSens assay, several pts were found to have advanced disease albeit a low viral load. Therefore, we wanted to compare the performance of NucliSens HIV-1 QT to Amplicor HIV-1 Monitor (v1.5), which was designed to detect a broad range of HIV-1 subtypes.
Methods: Blood samples were prospectively collected from pts with detectable viral load. Quantification of viral load was determined blindly in each sample using both Amplicor HIV-1 Monitor version 1.5 and NucliSens HIV-1 QT. Each sample represented a different pt. The results were compared by 2-tailed, paired t-test. Determination of viral subtype was done by sequencing.
Results: We compared 73 samples of subtype C and 34 samples of subtype B. Discordant results (> 0.5 log difference) were detected in 36% of subtype C samples (26/73), compared to 15% of subtype B samples (5/34). In all cases in which a discordant result was detected in subtype C, lower viral load levels were obtained with the NucliSens assay. In 16% of samples of subtype C (12/73), but only in 3% (1 sample) of subtype B, the difference between the assays was greater than one log. The discrepancy between the assays was highly significant for subtype C (p = 0.003), but not significant for subtype B (p = 0.14).
Conclusions: In pts with subtype C HIV infection, measurement of HIV RNA by the NucliSens assay resulted in statistically significant underestimation of the viral load in over 35% of the pts. Such underestimation of viral load may lead to suboptimal care of pts infected with subtype C virus, thus, limiting the use of specific commercial assays in increasing number of pts worldwide.
