- radiotherapy
Treatment
using radium or other radioactive matter.
- randomisation
A
process by which treatments are allocated to patients in a clinical trial on
the basis of chance alone. This means that the characteristics of the people
receiving each treatment should be similar at the start of the trial, so if
there are any differences in outcomes at the end of the trial, it can be
assumed that these are due to the treatment itself.
- randomised controlled trial (RCT)
The
most reliable type of clinical trial. In a trial comparing drug A with drug B, patients
are split into two groups, with one group receiving drug A and the other drug
B. After a number of weeks or months, the outcomes of each group are compared.
See also ‘randomisation’.
- range
The spread of values, from the smallest to the largest. The inter-quartile range (IQR) only includes the middle 50% of values and measures the degree of spread of the most common values.
- rapid virological response (RVR)
An undetectable hepatitis C RNA viral load within 4 weeks of starting treatment. An extended rapid virological response (eRVR) is when viral load is undetectable within 4 weeks and remains undetectable until at least week 12.
- rate
The number of events that we would expect to occur during a specified period of follow-up (e.g. 100 person-years). Particularly useful when follow-up periods vary from person to person in a study, or where a person may experience more than one event.
- recombinant
Genetically reconstructed.
- reconstitute
Mixing something which is in powder form (for example a drug) with water or
another liquid to make a liquid form of the substance.
- rectum
The last part of the large intestine just above the anus.
- regimen
A drug or treatment combination and the way it is taken.
- regression
Improvement in a tumour. Also, a mathematical model that allows us to measure the degree to which one of more factors influence an outcome.
- relapse
After dropping to
undetectable levels, hepatitis C RNA is detected again in blood after treatment
has ended. Different from ‘breakthrough’.
- relative rate
Comparing one group with another, expresses differences in the rate at which something occurs. A relative rate above 1 means the rate is higher in the group of interest; a relative rate below 1 means the rate is lower. Similar to ‘relative risk’.
- relative risk
Comparing one group with another, expresses differences in the risk of something happening. For example, in comparison with group A, people in group B have a relative risk of 3 of being ill (they are three times as likely to get ill). A relative risk above 1 means the risk is higher in the group of interest; a relative risk below 1 means the risk is lower. See also ‘absolute risk’.
- remission
Partial recovery from an illness, an alternative word for regression.
- renal
Relating to the kidneys.
- replication
The process of viral reproduction.
- representative sample
Studies
aim to give information that will be applicable to a large group of people (e.g.
adults with diagnosed HIV in the UK). Because it is impractical to
conduct a study with such a large group, only a sub-group (a sample) takes part
in a study. This isn’t a problem as long as the characteristics of the sample
are similar to those of the wider group (e.g. in terms of age, gender, CD4
count and years since diagnosis).
- response rate
The proportion of people asked to complete a survey who do so.
- response-guided therapy (RGT)
In which the length of treatment is individualized. Viral load at 4, 8, 12, or 24 weeks will determine for how
long treatment should be continued.
- retinitis
Damage to the retina, the light-sensitive surface at the back of the eye.
- retrospective study
A
type of longitudinal study in which information is collected on what has
previously happened to people - for example, by reviewing their medical notes
or by interviewing them about past events. See also ‘prospective study’.
- retrovirus
Family of viruses to which HIV belongs, that are distinguished by their use of RNA.
- reverse transcriptase
A retroviral enzyme which converts genetic material from RNA into DNA, an essential step in the lifecycle of HIV.
- ribavirin
An antiviral drug that
is used to treat hepatitis C in combination with other drugs.
- risk
See ‘absolute risk’.
- risk factor
An aspect of personal behaviour or lifestyle, an environmental exposure, or a personal characteristic that is thought to be associated with an infection or a medical condition.
- RNA
Ribonucleic acid, the
form in which a virus stores its genetic material.In hepatitis C, RNA (viral load) testing is used for diagnosis, to
help predict treatment outcome and to monitor response to treatment.