randomise – in research, this is a way of decide at random which participants join each group. So neither you or your doctor chose which group you join in a research study. A common example is that the decision would be made similar to tossing a coin.

More information from the i-Base guide to HIV research.

range – the highest and lowest results in a group. Range is used together with median (average). See IQR (interquartile range).

reinfection – catching HIV a second time. When an HIV-positive becomes infected with second strain or type of HIV. Sometimes called superinfection.

replicate – to duplicate, copy or reproduce. It is more scientifically accurate to refer to a virus replicating than reproducing.

resistance – when the genetic structure of an organism (virus, bacteria, fungi etc) changes in a way that stops a drug from working. See mutation.

Changing treatment and drug resistance.

resistance tests – tests to show changes to HIV that are associated with drug resistance. Genotype resistance test looks for genetic changes. Phenotype resistance test see whether individual drugs are still active when placed in a test tube with HIV.

Resistance tests.

retinitis – inflammation of the retina (in the eye). CMV retinitis is an HIV-related infection that can cause permanent vision loss in someone with a CD4 count that is below 50 cells/mm3.

CMV section of the training manual.

retrovirus – a family of viruses that includes HIV.

reverse transcriptase – an enzyme unique to HIV. It is used to convert single-strand RNA into double-strand DNA. This is needed before HIV’s genetic material can be integrated in the human DNA. HIV drugs that stop this process are called reverse transcriptase inhibitors (RTIs).

revertant mutation – this term is used in two ways.

Firstly when referring to a genetic change that shows the virus is returning from a drug resistant mutation back to a wild-type genotype. This can sometimes take several stages. For example, T215E/D/E and S are revertant mutations that can indicate the drug resistant mutation T215Y is being replaced by wild-type (i.e. T215T).

It can also refer to the fitness of a virus. A revertant mutation can refer to an additional mutation that allows the virus to regain viral fitness (most drug mutations also make the vurs less fit). The second example is called a compensatory mutation as is compensates for the reduced fitness caused by the first mutation.

ribavirin – drug used to boost the efficacy of pegylated interferon to treat hepatitis C. Given as twice-daily capsules.

RITA – this is a type of HIV test that can indicate whether you are likely to have been infected within the last six months.

RITA stands for Recent Infection Treatment Algorithm. In the UK this test is used to be called STARHS (Serological Testing Algorithm for Recent HIV Seroconversion).

See this Q&A on RITA testing.

ritonavir – a protease inhibitor (PI) that is now used boost levels of some other  HIV drugs, especially other PIs.

RNA – an abbreviation for the scientific word for genetic material found in some types of viruses. It is the abbreviation for ribonucleic acid. It is very similar to DNA but is single-strand rather than the double-strand in DNA. See DNA.