Acquired Immunodeficiency Syndrome
AIDS is the stage of the HIV infection where the immune system has clearly deteriorated and the body is less able to resist diseases. With current treatment methods, it is possible to get cured from the illnesses of the AIDS phase, and AIDS patients do not always die of AIDS-related diseases any more. Being HIV positive does not mean having AIDS.


The body of an HIV-infected person begins to produce antibodies against the HI virus soon after contagion. With all HIV-infected patients, antibodies are detectable in tests within three months from contagion. Tests of most people who have caught HIV show antibodies already within a month from contagion. HIV is diagnosed based on the determining of HIV antibodies.

Usually the antibody test is made from vein blood from the bend of the arm or a blood sample from the fingertip. An infected person can transmit the disease in an early stage even if the antibody test is still negative. A negative antibody test means that a person does not have an HIV infection if they have not been exposed to HIV during the last three months.


The antigen of HIV is a protein in the HI virus, which can be detected with a specific test from the blood sample of a person with HIV. With around half of HIV positive people, antigens can be detected from blood within the first few weeks from contagion or if they develop AIDS, but not otherwise. For the other half of HIV positive people, antigens are never found, so a negative antigen test result is not reliable on its own. The antigen test is often used in a combined test, which searches for HIV antibodies as well as antigens. Using the combination test is justified when a fresh infection is suspected, in which case HIV antibodies have not formed yet, but antigens could be discoverable.

Blood contact

Blood contact refers to a situation where a person has been exposed to another person’s blood. HIV can be transmitted from a person to another through blood either through intravenous drug use or through blood transfusion or organ transplants.

CD4 cell

T4 cell, a helper cell that regulates the functions of the immune system by detecting substances foreign to the body and by helping other lymphocytes in destroying pathogens. The amount of CD4 cells in the body indicate, along with other lab tests, how the HIV infection is progressing.

HIV risk

HIV risk refers to a situation where a person has been exposed to the HI virus. Such situations include oral, vaginal and anal sex, which has not involved using a condom the whole time or if the condom has broken. Other situations are blood exposure as well as sharing needles and syringes.

Mucous membrane contact

Mucous membrane contact refers to the physical contact of human mucous membranes. Mucous membrane contact is formed during unprotected oral, vaginal or anal sex. HIV can be transmitted in the above-mentioned mucous membrane contacts, but not through kissing.


Polymerase Chain Reaction, a form of blood test that detects e.g. the genomes of the HI virus in blood plasma. The test is used before beginning medical treatment, in medical treatment monitoring as well as for detecting possible medication-resistant virus strains. The method is very important for monitoring the efficiency of HIV medication. PCR tests are not used for diagnosing HIV infections.

Preventive medical treatment

A person exposed to HIV can be treated with a specific preventive medication, known also as post-exposure prophylaxis or PEP. PEP is considered when a person has been in sexual contact with an HIV positive person and the condom has broken. The person exposed to HIV should start with the treatment within 48 hours after exposure. The need for preventive medical treatment is evaluated by an ID specialist.

Primary HIV infection, or acute HIV infection

Around 30–50% of HIV-infected people are affected by a primary HIV infection in 2–6 weeks from catching the virus. The symptoms are much like a common cold: fever, a sore throat, swollen lymph nodes and so forth. Some people get a rash on their upper body. An HIV infection cannot be diagnosed based on the symptoms. Only an HIV test can provide reliable results on whether one is infected or not.

Rapid test

The HIV rapid tests deliver results in 1–20 minutes depending on the product used. It tests for HI virus antibodies (HIVab) or antigens and antibodies (HIV AgAb). The rapid test uses blood for detecting antibodies or antigens. At the moment, all quick tests available on the market are not reliable. It is therefore advised to get oneself tested at a health care office. A negative result from a rapid test is reliable, when it has been three months since the possible contagion.

Risk situation

In connection with HIV, risk situations are often mentioned. Risk situations refer to situations where HIV or some other STD could have been transmitted, such as during sexual contact or blood transmission. The accuracy of the definition of the risk situation is important for evaluating the reliability of the test result.

Serological window period

An HIV infection is diagnosed through HIV serology by determining antibodies. It may take up to three months for the body to produce antibodies caused by the HI virus. The window period refers to the period after contagion during which the infected is able to transmit the disease, but no antibodies are yet detectible in lab tests. Most HIV positive people do show positive results within a month from contagion.

Sub-types of the HI virus

There are two types of HI viruses, which are called HIV-1 and HIV-2. Both forms have further sub-types of their own.

T cell

Lymph cell or lymphocyte cell, a type of white blood cell that plays a central role in maintaining the body’s immune system. The HI virus weakens and destroys the help T lymphocytes’ functions in the body. See also: CD4 cell.


Virus Load, a value calculated with lab methods, which indicates the amount of HI viruses in the blood circulation. The amount of viruses and other lab tests help to determine the status of the HIV infection in the body.