Viral tropism

This is a test that is only used if you are going to use a CCR5 inhibitor.

Most people have HIV that uses a receptor on the surface of the CD4 cell called CCR5 to enable the virus to attach to the cell. In advanced HIV infection, the virus sometimes switches to a different receptor called CXCR4. After this switch, and also in people with a mixture of both receptors, a CCR5 inhibitor will not work.

For current tropism tests to work you need a detectable viral load of at least 500-1000 copies/mL. This means that you cannot use the tropism test if your viral load is undetectable.

However, genotype resistance tests can also predict tropism. If your viral load is less than 500, you can use a special type of resistance test (proviral DNA) to find out whether you can use a CCR5 inhibitor.

The only CCR5 inhibitor currently approved is maraviroc.