Dr. Holodniy -- welcome to The Body. It is my understanding that viral load tests measure the amount of virus in the bloodstream. Are there tests available that measure viral load in semen/elsewhere? If no, will there be? -- Clearly, if sex is the most common mode of transmission, this would be valuable test...

I ask because in this age of HAART/agressive therapies and undectable viral loads, I see a rationalization emerging surrounding unprotected sex, whether HIV+, not and/or in sero-discordant couples. Your comments please.

A very good question and important point. HIV, as measured by viral load tests, can be detected and quantitated in other body sites. We know that semen, spinal fluid, and vaginal-cervical secretions can have measureable viral load. Some of the viral load tests are better than others in measuring viral load in these other fluids. Some of the fluids contain inhibitors, which can affect the performance of the assays. Currently, viral load tests are only offered for blood. However, these assays are being used in research studies to determine the relationship between blood viral load and other sites. There is preliminary information that suggests that semen viral load levels decline with HAART, although not to the same dynamic degree. In addition, although semen viral load may become undetectable, this is only measuring cell free virus in seminal fluid. There are still HIV infected cells contained in semen, which current viral load tests will not measure. Therefore, despite undetectable blood plasma viral load, one should never assume that semen has become noninfectious.

MH