This glossary explains technical words used in the guide and the appendices.

Antibody – a part of your immune system that is produced to fight an infection. Each antibody recognises a specific antigen.

Antigen – a substance found on the surface of a virus or bacteria. An antigen is recognised by the immune system which then generates antibodies.

Binding site – the part of an antibody which interacts with the foreign organism like bacteria, fungus or virus.

CD4 count – a blood test that indicates the strength of the immune system.

Circumcision (male) – when the foreskin of the penis is surgically removed.

Confidence interval – the range of values where you are confident that the results were not due to chance.

Constant region – part of an antibody that is the same for every antibody made.

Diagnostic tests – used to diagnose whether or not someone has an illness.

DNA – (deoxyribonucleic acid) an abbreviation for the scientific word for genes and genetic material.

ELISA (Enzyme-Linked Immunosorbant Assay) – test to look for HIV antibodies and antigens.

Foreign organism – bacteria, virus, fungus or toxin found in the body which is not meant to naturally live there.

Genes – the different codes that each cell, person, organism is made from.

Genital fluid – the fluid that is released from the vagina or penis.

Genital tissue – the vaginal, penal or rectal skin.

GUM (Genito Urinary Medicine) clinic – place anyone in the UK can go to access sexual health services.

Immune system – the body’s defence against any foreign organisms.

Immunity – when the immune system already has generated protection to an infection.

Kilo Daltons (kDa) – a unit that is used for indicating mass on an atomic or molecular scale.

Mean – a type of average value. The mean is calculated by adding all results are added together and divided by the number of values.

Median – a type of average value. The median is calculated by arranging all the results of vales in numerical order. The middle value (or the half value between the two middle values if there are an even number of values).

Mucosal membrane – tissues that line openings in the body that are exposed to the external environment and internal organs. They are at several places and join with skin: nostrils, mouth, lips, eyelids, ears, genital tissue, foreskin and anus.

Mutation – a change in the genetic structure of an organism (including a virus like HIV).

Neutralise – to get rid of a threat by binding to it so that it cannot cause harm.

Optical density – the total energy (in this case light energy) at a given wavelength that passes through a filter. In this instance it is the amount of a specific colour or wavelength that is present.

PCR (Polymerase Chain Reaction) test– one of the most accurate test to detect and measure infectious genetic material.

Penetration – sexual intercourse.

PEP (Post-Exposure Prophylaxis) – a course of HIV meds (usually one month) to reduce the chance of infection.

PrEP (Pre-Exposure Prophylaxis) – using HIV meds before and after sex to stop the chance of infection.

POC (point of care) – HIV tests where results do not need to be sent to a laboratory. This includes self-testing and rapid tests.

Prevalence — this refers to how common a health condition is, usually given as a percentage of the general population.

Prevention – when something is stopped – ie when HIV is stopped from passing from one person to another.

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

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

Semen (cum) – male sexual fluid which is ejaculated from the penis during orgasm.

Seroconversion – an immune reaction where you develop antibodies to a new infection. With HIV, about 80% people remember some symptoms, some people become very ill and need treatment, and other have no symptoms.

Serostatus – whether someone is HIV negative or HIV positive.

Sexually Transmitted Infections (STIs) – infections which are passed from sexual contact.

Symptoms – a change in a function, sensation or appearance of a person that indicates a disease or disorder. For example, a fever, headache or nausea can all be symptoms of flu.

Target cell – a cell that a virus needs to infect in order to establish infection in someone.

Transmission – when an infection is passed from one person to another.

Undetectable viral load – when the amount of HIV (viral load) is less than 50 copies per millilitre (/mL) of blood.

U=U (Undetectable=Untransmissible) – having an undetectable viral load means HIV cannot be transmitted sexually.

Unprotected sex – this historically referred to sex without a male or female condom. This is not necessarily an accurate term now that treatment is now recognised as being protective.

Variable region – this refers to the part of the antibody that changes so it is specific to the organism it is designed to attack.

Viral load – the amount of virus (for example in blood, genital fluids or tissue sample).

Viral shedding – the term used to refer to release of infectious particles from one type of cell or part of the body into another part of the body.

Western blot – a test that can diagnose HIV by looking for antibodies to a variety of HIV antigens. This test uses electrical current and molecular weight to differentiate between the different protein antibodies.

Window period – the time it takes from HIV entering your body to your immune system generating a response.

Last updated: 1 June 2021.