Clinical Importance

Getting Tested

Slide Rule

Only one of these products, AMPLICOR HIV-1 MONITOR™ Test , is currently approved by the US Food and Drug Administration, and has been used by six of the last eight pharmaceutical companies for their new drug discovery trials. One advantage of the AMPLICOR HIV-1 MONITOR™  Test and NucliSens™ HIV-I QT Test is their sensitivity. AMPLICOR HIV-1 MONITOR™ Test can detect as few as 50 copies of viral RNA per mL of plasma and NucliSens™ HIV-I QT Test as few as 80 copies/mL.

All three tests measure viral load from a blood sample. The amount of virus in the blood represents only two per cent of the total virus in the body. However, recent studies have shown that viral load can be used to accurately predict HIV disease progression. Some virus is found in the lymphatic system and other body tissues.

In this test, the single stranded HIV RNA present in the sample is converted to DNA. This process is called reverse transcription.

The DNA strands are then amplified by Polymerase Chain Reaction (PCR), detected and measured. This test measures from 400 to 750,000 copies of virus particles by the standard method and down to 50 copies/mL by the UltraSensitive method.

Click here for more information on the AMPLICOR^® Testing Method (link)

With the bDNA assay, numerous probes bind to the HIV RNA The quantity of HIV-1 RNA is measured at the level found in the sample without amplification of the material.

The bDNA Version 2.0 test can detect from 500 to one million copies of HIV per sample. The version 3.0 test is in beta sites currently and is expected to reach 50 copy sensitivity. It requires a much larger sample of blood than the other two tests - 2mL (several tablespoons) compared to only 100 and 200 microlitres required for NASBA and AMPLICOR HIV-1 MONITOR™ respectively.

During a NASBA assay a primer is added and annealing, extension and amplification of HIV RNA takes place. Post-amplification, chemicals are added to the solution which cause a chemical reaction resulting in the emission of light (luminescence). The intensity of the luminescence is measured to calculate the viral load.

NASBA is able to detect 400 to ten million copies of virus particles per sample in the standard assay and down to 80 copies in the more sensitive version of the assay.

New Tests

The techniques for testing for viral load are constantly being updated, modified and improved. Each new ‘generation’ of test is designed to be more accurate and more sensitive than the previous version.

Roche Diagnostics has developed a more sensitive test, AMPLICOR HIV-1 MONITOR™ with the UltraSensitive Sample Preparation Method, that is able to detect to 50 copies of HIV particles. This increased sensitivity gives physicians and patients with HIV a more accurate measure of viral load, resulting in better management of the disease and allows for more effective treatment. Each individual’s management can then be reviewed in light of their viral load and in conjunction with their general health, CD4 cell count, previous therapies and other factors.

Testing in Different Clinics

It is advisable to use the same clinic/laboratory and assay method for serial tests of the same individual. This will avoid variations between methods which may cause variation in results.