Question

What does a viral load of 2.8 mean?

14 June 2007. Related: All topics, CD4 and viral load.

I have been given my viral load – it has been expressed as 2.8.

What does this mean? I thought viral loads were expressed in the 10,000 and 1000,000 etc

Answer

Answer: Simon Collins

A viral load of log 2.8 = a viral load of about 650 copies/mL.

You are right that viral load results are usually given as larger numbers – and can be anywhere from 50 copies/mL to over 1,000,000 copies/mL.

Another way of expressing numbers that have a large range though is to use a log scale. This is where the actual number is expressed as a factor of 10.

• 1 log = 10
• 2 logs = 10×10 = 100
• 3 logs = 10x10x10 = 1,000
• etc

Another way to remember the conversion is that the number of ‘zeros’s is the same as the log number: 5 logs is 1 with 5 zeros, or 100,000.

For log numbers in between whole numbers:

• 1.3 logs = approximately 20 copies/mL
• 1.5 logs = approximately 32
• 1.7 logs = approximately 50
• 2.7 logs = approximately 500
• 4.7 logs = approximately 50,000

We’ll add a conversion table to the i-Base website over the next week or so, with a link to this question, so it is easy to check again in the future.

One of the ways that ‘logs’ make life easier, is that guidelines recommend that when you start treatment your viral load should drop by at least 1 log within 4 weeks. This gives a simple target for people who could be starting at very different viral loads – eg 20,000 copies/mL or 500,000 copies/mL.

If you have just started treatment, you will be aiming to get your viral load to under 50 copies/mL – or below 1.7 logs.