Units of measure – mm3, mL, μL etc
CD4 and viral load are measured in different volumes.
CD4 counts are measured in cells per cubic millimetre = cells/mm3
A cubic millimetre (mm3) = mm3 = mm3 = 1 mm x 1 mm x 1 mm.
= microlitre (µL).
= a metric measure of volume or capacity equal to a cube that is 1 millimeter on each edge.
Sometimes CD4 is written as cells/µL = cells/microlitre = millionth of a litre.
Sometimes CD4 results are written as cells / log x 106 (ie x 10 x 10 x 10 x 10 x 10 x 10).
If your CD4 count is 200, this can be written:
- 200 cells/mm3
- 200 cells/µL
- 200 x log106 cells/L
- 0.2 x log109 cells/L
Viral load is measured in copies per millilitre = copies/mL
A cubic centimetre (cm3) = millilitre (mL)
= one cubic centimetre = 1cm x 1cm x 1 cm = cm3 = cm3.
= one mL = 1000 µL.
= a metric unit of volume equal to one thousandth of a litre.
Viral load of 20,000 is written:
- 20,000 copies/mL
- 20,000 c/mL HIV RNA.
- This is sometimes written 2.0 x 10 (x). The letter “x” can be any number from 1 to 8 to show whether you are multiplying by 10, 100, 1000, 10 000, 100 000 etc. In this case it would be 2.0 x 104 – ie 2.0 x 10,000.
- Using a log scale this would be 4.3 log10 copies/mL.
Conversion table between viral load as numbers and logs.
1,000 microlitres = 1 millilitre
1,000 millilitres = 1 litre
1,000,000 microlitres = 1 litre
[1 US pint = 0.47 litres]
If there are 5.5 litres of blood in your body:
Q1. How many millilitres (mL) of blood are in your body? A. _______
Q2. How many microlitres (µL) of blood are in your body? A. _______
[Answers: Q1: 1000 x 5.5 = 5,500; Q2: 1000 x 1000 x 5.5 = 5,500,000]
Last updated: 16 September 2016.