Understanding “Log” Changes
Changes in viral load—the number of copies of HIV’s genetic material found in a sample of blood—are often expressed as “log” changes. This term refers to scientific notation, which uses powers of 10 to keep large numbers manageable.
For example, a 1-log reduction is a reduction by 10 times the original amount. For example, if a person starts antiretroviral therapy with a viral load of 100,000 copies/mL and has a viral load of 10,000 copies/mL at the next visit, that’s a 1-log reduction.
Here’s a handy cheat sheet:
- 1-log reduction = 10 times smaller
- 2-log reduction = 100 times smaller
- 3-log reduction = 1,000 times smaller
- 4-log reduction = 10,000 times smaller
- 5-log reduction = 100,000 times smaller