Viral load as a surrogate end point in HIV disease

OBJECTIVE: To examine the role of viral load as a surrogate end point for HIV disease progression and death. DATA SOURCES: A MEDLINE search was conducted for the years 1990-March 2001. In addition, relevant articles were cross-referenced to screen for additional information. STUDY SELECTION AND DATA EXTRACTION: Data regarding the validity of viral load as a surrogate end point for disease progression or death are cited. Emphasis was placed on randomized, controlled trials, but descriptive studies are also included. DATA SYNTHESIS: Recently, viral load has emerged as an important biomarker for monitoring HIV disease and antiretroviral therapy. Both baseline viral load and changes in viral load with time predict HIV disease progression and death. In fact, disease progression increases consistently once viral load exceeds 10,000 copies/mL, and AIDS and death primarily occur in patients with viral loads > 100,000 copies/mL. Changes that occur in viral load after initiation of antiretroviral therapy, however, do not fully explain the entire treatment effect. Also, separate comparisons of antiretroviral regimens may demonstrate similar differences in viral load changes but not similar differences in disease progression. CONCLUSIONS: Viral load is an important monitoring parameter for HIV disease and antiretroviral therapy. However, changes in viral load do not explain the entire clinical improvement that occurs after initiation of therapy. Although viral load is a clinically important surrogate end point for HIV disease, it cannot fully account for all associated treatment effects.