Blood tests before starting or changing HIV treatment

A close up of a person's arm while they are having their blood taken. The person taking the blood is wearing surgical gloves. We can see some of the blood is already in the tube.
Image: Chompoo Suriyo/

 Key points

  • Before choosing a treatment, your blood should be checked for resistance to different medications.
  • A viral load test one month after starting new anti-HIV drugs provides important information about your response to treatment.

Before you start taking HIV treatment, or if you need to switch to a new combination, you should have a number of blood tests. 

To help make sure that you start with an effective combination of anti-HIV medications, you should have a blood test to see if your HIV has resistance to any antiretroviral drugs. This is because it is possible for a strain of HIV that has already developed resistance to some drugs to be passed on to someone who has not taken those drugs.

Your clinic will usually also do a genetic test (called HLA-B*5701) to see if you are more likely to develop an allergic (hypersensitivity) reaction to the anti-HIV medication abacavir (Ziagen, also in the combination pills Kivexa and Trizivir).

Your clinic will also test you for hepatitis B and C, and run tests to look at your blood sugars, as well as the health of your liver and kidneys. The results of these tests will help you and your doctor decide the best treatment for you, and when you should start.

Viral load and CD4 tests will tell you about the health of your immune system and if your treatment is working effectively.



A drug-resistant HIV strain is one which is less susceptible to the effects of one or more anti-HIV drugs because of an accumulation of HIV mutations in its genotype. Resistance can be the result of a poor adherence to treatment or of transmission of an already resistant virus.

viral load

Measurement of the amount of virus in a blood sample, reported as number of HIV RNA copies per milliliter of blood plasma. Viral load is an important indicator of HIV progression and of how well treatment is working. 


undetectable viral load

A level of viral load that is too low to be picked up by the particular viral load test being used or below an agreed threshold (such as 50 copies/ml or 200 copies/ml). An undetectable viral load is the first goal of antiretroviral therapy.


An essential organ involved in digestion of food and excretion of waste products from the body.


How well something works (in real life conditions). See also 'efficacy'.

When you start or change a drug combination, a viral load test will be done within the first month, to check that the treatment is working. After this, testing is generally performed every three to six months, although it may be more often to begin with and then less frequently once you are stable on treatment and doing well.

If you need to change HIV treatment because your viral load becomes detectable again, your choice of new medications should be guided by having another resistance test at this stage to see which drugs will work for you. 

If you need to change treatment because your current HIV treatment isn’t controlling your viral load, it’s important that you do this in good time to reduce the risk of resistance. How quickly you need to do this will depend on which anti-HIV drugs are taking; your healthcare team will discuss this with you. 

Even if you have resistance to several drugs, the range of anti-HIV drugs available now means there will still be options for you.  An undetectable viral load is a realistic objective for nearly everyone, including people who have taken a lot of different treatments in the past and have drug-resistant virus.

Once you are on HIV treatment, you will continue to have tests to measure liver and kidney function, and the levels of fat (cholesterol) and sugar in your blood, to assess any effects of the drugs on these systems. Some of these are done every time you attend and some once a year.

In some situations, your doctor may start or switch your treatment before results of all the tests are known.  If this is the case, your doctor should discuss this with you. You should still be given the results of all your tests when they are available.

Your HIV care will also involve a number of other routine tests. These will monitor your general health, to see if your treatment is causing any side-effects.

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