Progress in Quantitative Viral Load Testing: Variability and Impact of the WHO Quantitative International Standards

Area of Science:

• Virology
• Molecular Diagnostics
• Clinical Laboratory Science

Background:

• Interlaboratory agreement in viral load testing is crucial for patient management.
• The impact of World Health Organization (WHO) quantitative standards on this agreement remains under-evaluated.
• Quantitative PCR (qPCR) assays are widely used for viral load quantification.

Purpose of the Study:

• To assess interlaboratory variability in quantitative PCR assays for common viruses.
• To evaluate the effect of WHO quantitative standards and international unit calibration on result variability.
• To identify challenges in viral load testing accuracy.

Main Methods:

• Analysis of proficiency testing survey data from 554 laboratories.
• Evaluation of quantitative PCR assay results for cytomegalovirus (CMV), Epstein-Barr virus (EBV), BK virus (BKV), adenovirus (ADV), and human herpesvirus 6 (HHV6).
• Stratification of results by assay manufacturer and calibration to international units/ml.

Main Results:

• High interlaboratory variability was observed for all tested viruses, with ranges up to 5.66 log10 copies/ml.
• Adoption of international units/ml showed some improvement in result variability, particularly for EBV.
• Variability remains a significant challenge across all tested viral load assays.

Conclusions:

• Interlaboratory variability in viral load testing is a persistent issue despite the availability of WHO quantitative standards.
• Calibration to international units/ml can help reduce variability, with varying degrees of impact across different viruses.
• Further efforts are needed to enhance standardization and improve the reliability of viral load testing.