High Level of Correlation of Human Papillomavirus-16 DNA Viral Load Estimates Generated by Three Real-time PCR Assays Applied on Genital Specimens

Human papillomavirus-16 (HPV-16) viral load could be a biomarker predictive of the presence of high-grade cervical lesions. Recently, several real-time PCR assays have been developed to accurately measure HPV-16 viral load. However, results from various reports using these assays cannot be compared because interassay test correlation has not been documented. The variability of HPV-16 DNA quantitation was assessed by comparing three real-time PCR assays (HPV-16 L1, HPV-16 E6, and HPV-16 E6 PG) applied on 144 genital samples (125 cervicovaginal lavages and 19 specimens collected using vaginal tampons) obtained from 84 women (66 HIV seropositive and 18 HIV seronegative). Correlation was greater between the HPV-16 E6 assays [correlation coefficient (rho) = 0.92] than between each E6 assay and HPV-16 L1 assay (rho = 0.83 and 0.84, respectively). The median HPV-16 copies measured by HPV-16 E6 PG (14,609 HPV-16 copies/2 muL sample) and HPV-16 E6 (18,846 HPV-16 copies/2 muL) were similar (P = 0.27) but were both greater than the median HPV-16 copies measured with the L1 assay (4,124 HPV-16 copies/2 muL; P < 0.001). Correlations between HPV-16 E6 assays were similar for samples containing non-European (rho = 0.93) or European (rho = 0.95) variants. However, the correlation between HPV-16 L1 and HPV-16 E6 PG or HPV-16 E6 was lower for specimens containing non-European variants (rho = 0.80 and 0.76, respectively) compared with specimens containing European variants (rho > 0.85). HPV-16 DNA quantity estimated with the three assays was comparable although lower with the HPV-16 L1 assay. The level of correlation depended on viral polymorphism, viral load, and cervical disease status.