Glossary

genotype test – a test that looks at how the genetic structure of a sample of HIV and whether the virus has changed with drug resistant mutations.

CD4 count – number of CD4 cells in a cubic millimetre of blood. CD4 counts results are given as a number that can be anywhere from 0 to over 2000 (rarely).

The range for an HIV-negative person is usually quoted as 430 – 1690. This means 95% of HIV negative people have a CD 4 count between 430 and 1690, but also that a few people have normal levels above or below this. A ‘normal’ CD4 count for an HIV positive person means getting above 500. However, this is an ideal goal and many people remain very well and healthy with CD4 counts that are lower than this.

Test results can also be reported in three main formats. ie a CD4 count of 350 can be written as:

• 350 cells/mm³ (cells per cubic millimetre); or
• 350 cells/μL (cells per microlitre); or
• 350 Χ 10⁶ cells/L (per million cells per litre: i.e.: times 10 to the power of 6, cells per litre)

See: Units of measure.

Since 2015, most treatment guidelines recommend starting treatment at any CD4 count, even when this is above 500.

Once viral load becomes undetectable on HIV treatment (ART), this also stops sexual transmission to HIV negative partners.

trimester – a 12 week period of a pregnancy. Different periods during pregnancy are commonly referred to as the first, second and third trimester.

median (average) – where the results are all arranged in numerical order and the middle of the range is taken as the (median) average. See mean.

What is an average.

haemoglobin – substance in red blood cells that carries oxygen.