Understanding Viral Load Assays for Cytomegalovirus and Epstein-Barr Virus

Logarithmic (log) Processes

March 2010

During an active infection, each time a virus infects a cell, it may produce 10s or 100s of viruses. Then, each of these viruses infects other cells and produces 10s or 100s more viruses. This is an example of exponential growth, which is best measured on a logarithmic scale.

Similarly, in the laboratory, most viral load assays use polymerase chain reaction, or PCR. PCR typically uses 25-50 cycles of amplification. Each cycle doubles the amount of a target sequence of nucleic acid. This is also a logarithmic process.

Since both the biological phenomenon and the laboratory method measuring it grow logarithmically, it makes sense to think about viral loads in log terms.

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• Introduction
• Cytomegalovirus and Epstein-Barr Virus Background
• Patients and Immunosuppression
• CMV in Transplant Patients
• When to Treat CMV?
• CMV Treatment Strategies
• EBV and Posttransplantation Lymphoproliferative Disorder
• When to Treat EBV?
• Treatment for EBV Infection or PTLD
• The Balancing Act of Transplant Immunology
• The Balancing Act of Transplant Immunology: Less immunosuppression
• The Balancing Act of Transplant Immunology: More immunosuppression
• The Balancing Act of Transplant Immunology
• Crucial Questions
• Viral Load Assays
• Viral Load Assays, cont.
• Variability
• Ideal Standards
• Comparing Results
• Logarithmic (log) Processes
• Advantages of Logarithmic (log) Numbers
• Integer, Scientific Notation, Logarithm
• Log vs Fold
• Disadvantages of Log
• Remember These?
• System Precision/Imprecision
• What is Significant Change?
• Reality Check
• Literature is Helpful But...
• Interpreting Viral Loads
• Review
• References
• Questions?