HIV viral loads

Microbiology

Notes

 

  • HIV viral load is the quantifiable measurement of HIV Type 1 in human plasma
  • Further specialist tests for HIV positive patients include HIV resistance tests and HIV Proviral DNA PCR
  • Samples for HIV viral load must reach the laboratory within 6hrs of collection and must be received before 16.30hrs Monday to Friday
  • This assay is NOT intended as a diagnostic test to confirm the presence of HIV-1 infection
  • Please telephone the laboratory when these samples are collected

Sample requirements

Plasma - paired samples not required

4ml of blood taken into an EDTA Tube

For adults 2 full EDTA tubes required for each test -  eg. for HIV viral load and resistance, 4 EDTA tubes in total are required.

 

 

For babies and small children a minimum of one full 2mL paediatric EDTA or one full paediatric Mini Collect EDTA tube is required

4 mL EDTA tube

 

 

2 mL paediatric EDTA tube

     Paediatric Mini Collect EDTA tube

Required information

  • Relevant clinical details
  • Time of sample collection

Storage/transport

Transport immediately at ambient temperature

Turnaround time

Adult HIV viral loads:

Tested in house

Up to 10 days

 

Paediatric HIV viral loads, resistance testing and Proviral DNA PCR:

Sent to a Regional Reference Centre

Up to 10 days

Results

Reported in copies/mL and log copies/mL

In house assay Lower limit of detection: 30 copies/mL 1.47 log copies/mL
  Upper limit of detection: 10 million copies/mL 7.0 log copies/mL
Reference Centre assay Lower limit of detection: 40 copies/mL 1.6 log copies/mL
  Upper limit of detection: 10 million copies/mL 7.0 log copies/mL

Result interpretation

  • The assay is subject to some natural variation, but we would not expect this to exced a 0.5 log difference when testing the same patient sample on two separate occasions. This also means that two separate samples from the same patient may naturally vary by up to 0.5 log without any underlying change in viral load and that samples may on occasion fluctuate around the cut-off from negative to positive or vice versa - see Viral Load Ready Reckoner PDF file
  • Where two consecutive samples show an increase in viral load less than 0.5 log without an obvious cause we would remark on this in the report. i.e.

"This result and the previously reported result remain within the accepted normal variablilty of the assay (0.5 log copies/mL)."

  • Where two consecutive samples show an increase in viral load greater than 0.5 log without an obvious cause we would automatically re-test the most recent sample if sufficient sample remains.
  • Where two consecutive samples show a change from negative to positive regardless of the degree of difference we would automatically re-test the most recent sample if sufficient sample remains.
  • Where a sample is repeated we will report both results.
  • Based upon our own data for 2012-2013 the variability of the assay has not exceeded 0.3 log
  •  See also:

 

Page last reviewed: 22/12/2014