Quantitative nucleic acid amplification methods for viral infections.

BACKGROUND Over the past 2 decades there have been substantial improvements in the methods used to quantify viral nucleic acid in body fluids and in our understanding of how to use viral load measurements in the diagnosis and management of patients with a number of viral infections. These methods are now integrated into a wide range of diagnostic and treatment guidelines and commonly deployed in a variety of clinical settings. CONTENT Quantitative nucleic acid amplification methods that are used to measure viral load are described along with key issues and important variables that affect their performance. Particular emphasis is placed on those methods used in clinical laboratories as US Food and Drug Administration-cleared or laboratory-developed tests. We discuss the clinical applications of these methods in patients with HIV-1, hepatitis C virus, hepatitis B virus, cytomegalovirus, Epstein-Barr virus, and BK polyomavirus infections. Finally, the current challenges and future directions of viral load testing are examined. SUMMARY Quantitative nucleic acid amplification tests provide important information that can be used to predict disease progression, distinguish symptomatic from asymptomatic infection, and assess the efficacy of antiviral therapy. Despite the advances in technology, large challenges remain for viral testing related to accuracy, precision, and standardization. Digital PCR, a direct method of quantification of nucleic acids that does not rely on rate-based measurements or calibration curves, may address many of the current challenges.