Glossary of Concepts and Terms (underlined words)

Adherence

Refers to the practice of accurately following ("adhering to") the directions given for the use of a drug regimen, such as taking the prescribed number of pills at the appropriate times of the day and observing any specific meal requirements. Adherence plays a central role in determining the success of anti-HIV therapy and several reports have shown that resistance to HIV drugs can develop more quickly when a person makes a habit of missing doses of their medication. Therefore, it is important to try to make anti-HIV therapy as compatible with one's life circumstances as possible so that there is little pressure to miss doses.

Baseline Viral Level

The initial measurements (usually 2) of viral level, such as at the start of a study, which are used as a reference point for later measurements, allowing for an evaluation of the results.

CD4+ Cells

CD4+ (CD4 positive) cells are a type of white blood cell that have a marker on them called the "CD4" receptor. These cells play a critical role in managing the human immune response and controlling infection. Also called "T-helper cells," "T4 cells," or, less accurately, "T-cells."

CD4+ Counts

CD4+ count is the number of CD4+ cells found in a particular blood test. This count is the most commonly used measure of immune health, but is by no means the only one. HIV infects and leads to a gradual loss of the body's CD4+ cells. A significant drop in CD4+ cell count (below 500 or lower) reflects damage to the immune system. A drop below 200 usually indicates damage sufficient to lead to the risk of opportunistic infections.

Drug Resistance

The ability of a disease-causing organism to continue growing and reproducing despite the presence and activity of a drug or drugs designed to suppress that organism's growth. In HIV, this happens when the virus mutates -- or changes in process of reproduction -- in a way that makes new copies of the organism insensitive or less sensitive to particular anti-HIV drugs. Once resistant mutants are produced, they can grow rapidly despite the continuing presence of the drug. People with higher HIV levels are more at risk for developing drug-resistant HIV, as are people with developed resistance to similar drugs.

HIV Disease Progression

The process of growth, spread and development of symptoms and effects of HIV disease, including the general decline of the health of the immune system. Indications or "markers" of disease progression include HIV levels, CD4+ cell count, and the presence of several known symptoms of disease, opportunistic infections and overall general health. Individuals have a highly variable rate of disease progression.

Viral Load

The amount of virus measurable in blood or other fluid or tissue. The viral load number has been shown to be a good predictor of the rate of HIV disease progression.

"Undetectable" or Viral Load Below the Limit of Detection

A viral load measurement below the lower limit to which a particular form of viral load test can reliably count (for the most standard tests, the lower limit of detection is around 400-500 copies per cubic milliliter per blood). It does not mean the virus is not there, just that it is too low to measure in the bloodstream with the standard test. "Supersensitive" or ultra-sensitive versions of viral load tests are available which can accurately measure as low as 20-50 copies of virus. Suppressing viral load below the limit of detection is one of the most important ways of making sure that the benefits of therapy last as long as possible