Understanding The Science

A guide to the differences between HIV in blood and HIV in semen, the HIV semen test, “sperm washing,” and how SPAR developed the most stringent safety standards for semen testing in the world.

HIV in Blood VS. HIV in Semen

Research has shown that an HIV blood test is not a reliable predictor of viral burden in semen. These studies have revealed that semen producing organs are a separate compartment of HIV infection, and that semen viral burden is different from blood viral burden, even in men on therapy. For this reason, Bedford scientists have structured SPAR around semen testing and using sperm only from specimens that test undetectable for HIV.


Data compiled by BRF scientists in 2006 revealed that 24% of the semen specimens from 262 men entering SPAR were positive for HIV, even though the men had an undetectable burden of viral RNA (HIV particles) in blood. All men eventually produced at least two specimens with undetectable virus.

This important finding, that HIV is intermittently present in semen specimens, is what makes testing each specimen for virus so important to prevent virus transmission.