‘Viral load’ is the term used to describe the amount of the HIV virus present in your bloodstream. Knowing how much HIV is present is an important indicator of how much your immune system is at risk of damage, how well your treatments are working, and whether you should consider starting or changing treatments.

A viral load test is a blood test, the result of which is given as the number of viral copies of HIV per millilitre of blood. A ‘copy’ is what HIV produces every time it grows inside a cell: the more copies, the more virus.

The amount of virus in your blood may range from a very small number of copies in your blood (below 20 copies per millilitre of blood) to levels in the thousands, hundreds of thousands, or even millions.

Viral load is simply a count of the virus expressed in number per millilitre.

When you first have your viral load tested, you may have two tests several weeks apart, which gives a result known as your ‘baseline’, and which can be used to compare changes over time. These results can be a useful guide for considering treatment. Another concept you Doctor might discuss is viral ‘set point’. This is the viral load six months after infection once you immune system has had a chance to respond.

a) ‘Undetectable’ viral load?

One result you can get back from a viral load test result is ‘undetectable’. Undetectable viral load does not mean that you have ‘cleared’ the virus from your body. It means that HIV is present, but in amounts so small they cannot be detected by current commercial tests. The current limit of detectability is 20 copies per millilitre of blood. Virus at such levels is replicating so slowly that little, if any, damage will be happening to your CD4 cells and immune system.

Undetectable viral load does not mean the virus has been eradicated from your body. HIV infects a variety of different cells in the body and remains ‘latent’ in resting T cells even when treatment is working effectively. A current focus of HIV cure research is figuring out how to treat this latent virus.

b) Detectable viral load results

You may be told that your viral load result is ‘high’ (i.e. more than 100,000 copies per ml), ‘moderate’ (i.e. 10,000 to 100,000 copies per ml), or ‘low’ (i.e. less than 10,000 copies per ml). On their own, detectable viral load results are no cause for alarm. For example, a high viral load result does not mean you are going to get sick immediately; or a low result, after having been undetectable for some time, does not necessarily mean your drugs have suddenly failed. Viral load “blips” are not uncommon.  Usually this means a previously undetectable viral load has risen to detectable at a low level e.g. 80 copies/ml and that the viral load will return to undetectable next test.  It is unclear what blips mean.  It may mean that resting T-cells in HIV reservoir sites have been activated for some reason, for example by a vaccination.  If the viral load returns to being undetectable, there is no need to consider a resistance test and a change in treatment.

Your viral load level is a rough guide to the likelihood of future damage to the immune system. So if your viral load is high it means that future damage is more likely. If it is low or undetectable it means future damage is less likely.

In order to make decisions about treatments, the viral load has to be read in conjunction with the CD4 cell count.

Viral load and the pattern over time is important

You may be asked to have viral load tests fairly frequently initially so you and your doctor can keep track of changes over time, or of any sudden variations between test results. In fact, an unexplained and significant upward trend in viral load over a number of tests may be a better indicator that you should consider changing or starting treatments than a single, detectable result in isolation. The magnitude of the change is important. For example, a rise of viral load from 5,000 to 6,000 does not necessarily indicate there is a problem. But a rise from 5,000 to 50,000 may suggest that the virus is beginning to replicate very rapidly for some reason, and that you should take this into consideration when thinking about starting or changing treatments.

Log (or logarithmic) scale

Changes in viral load are sometimes reported as logarithmic or “log changes.” This mathematical term denotes a change in value of what is being measured by a factor of 10. For example, if the baseline viral load is 40,000 copies/ml of blood, then a 1-log increase equals a 10-fold (10 times) increase, or 400,000 copies/ml of blood. A 2-log increase equals 4,000,000, or a 100-fold increase. An easy way to figure out log changes is either to drop the last “0” or add “0” to the original number.

Other factors can affect viral load

No one viral load result should be considered alone. It’s the pattern over time that counts. There are a number of reasons why you may experience a sudden, temporary rise, or ‘spike’ in your viral load. These include:

• another infection (e.g. the ‘flu, hepatitis, or another sexually transmissible infection such as gonorrhoea or syphilis)
• recent vaccination (e.g. routine travel-related vaccinations or hepatitis A or B vaccination), which can stimulate your immune system for a brief period causing only a temporary rise

Viral load over time without treatment

This is a typical picture of viral load over time. Soon after initial infection there is a peak in viral load until the immune system responds. Then, for a period of years the immune system and the virus are engaged in a balancing act, though in nearly all cases the immune system is still being weakened. Throughout this period, the virus is still active. Eventually, the virus may overwhelm the immune system.

When you first have your viral load tested, you will usually have two tests a few weeks apart, which gives a result known as your “baseline”, and which can be used to compare changes over time. These results can be a useful guide if you are considering treatment. The level to which the viral load settles six months after infection is called the set point.  For some people, this set point is low, say <10,000 copies/ml (Elite controllers mentioned above).  A set point of >log 5 that is >100,000 copies/ml, would mean that you doctor would suggest more frequent monitoring.

If you are not taking antiviral treatments, you will probably be advised to have a viral load test each time you have a CD4 or T-cell count. Comparing these results with your baseline viral load will alert you and your doctor to any changes in your immune system or your health.

Ask your doctor to explain the meaning of any changes in your viral load. It is quite common for viral load to change a bit with each test. What is important is the magnitude of the change. Doctors use a mathematical scale called a logarithmic scale to measure the significance of any changes. It is only changes of a significant magnitude that are considered important.

Viral load tests tell you how much virus is in your blood. But HIV is also present in other body fluids, including CSF (cerebrospinal fluid) — the fluid which protects your brain — and semen and vaginal fluids. The level of virus in your blood can be different to the amounts in other body fluids. Nonetheless, recent research suggests that HIV viral load is a good guide to infectiousness. If you have maintained an undetectable viral load for six months or more, take your medication as prescribed and have a regular doctor’s check-up you can be reasonably confident you will not pass on HIV through sexual intercourse. Of course using condoms is an added protection and will reduce the risk to virtually zero.  Sexually transmissible infections may cause genital tissue to activate HIV so, if you are at risk, frequent STI screening is needed.

The other test that is critical in managing and understanding HIV is the CD4 or T-cell count.

CD4 cells are a critical part of your immune system that are infected and destroyed by HIV. Sometimes, they can be depleted to such levels that they are unable to play their part in the immune system. If this happens, you could be at risk of developing opportunistic infections or AIDS related illnesses.

The CD4 count is a measure of the damage already done. The viral load is a measure of the risk of future damage. A general guide to CD4 test results is:

• 500 to 1,350 CD4 is the ‘normal’ range for adults
• more than 500 CD4 indicates little or no immune system damage
• between 500 and 250 CD4 cells indicates some damage but it is unlikely you will be at risk of major opportunistic infections, and
• less than 250 CD4 indicates more serious immune system damage and suggests that you could be at risk of serious opportunistic illnesses.

CD4 percentages measure the proportion of CD4 cells against another type of white blood cell called CD8. Many doctors believe that the percentage is a more accurate indication of the stability of CD4 over time, rather than the actual CD4 count. This is because the total number of white blood cells can vary over time. For example, a person with a CD4 count of 350 at 30% could indicate more stability and less chance of disease progression than a person with a CD4 count of 500 at 20%. A normal percentage of CD4 in an HIV uninfected person is 30-50%.

Along with viral load and the CD4 count, CD4 percentage is another result that is used by your doctor to determine your optimal treatment strategies.

To get the best picture, viral load test, CD4 counts and CD4 percentage results should be considered together. These results can be used to determine:

• the level of activity of the virus in your blood stream
• the level of damage to your immune system
• when to start treatment
• if the current treatments are working, and whether it may be necessary to change treatments
• when to take preventive medicines (prophylaxis) to decrease the chances of getting an opportunistic illness

People with HIV typically have blood tests every 3 to 6 months. In addition to CD4 and viral load a range of other tests may be done to monitor your general health and look for drug side-effects. The results of these tests may also influence decisions to commence or change your HIV treatments or add other medications to manage the side-effects.  When people are stable on treatment, monitoring blood tests are needed less often, such as 6 to 9 monthly.

Monitoring involves more than CD4 and viral load.  The Australian standard is to check the full blood count, liver and kidney function and glucose every time and to check on lipids (cholesterol and triglycerides) at least annually.

Some of the common tests include:

Glucose, triglyceride and cholesterol levels  The two major types of fat (lipids) in the blood are triglycerides and cholesterol. Glucose, triglyceride, and cholesterol levels are most reliably measured while fasting: in the morning before eating breakfast. Certain anti-HIV therapies can increase cholesterol, triglyceride, and glucose levels in some people, which may increase the risk of heart attack and stroke, and can be associated with lipodystrophy (the redistribution of body fat).

Liver function tests  There are a range of tests which taken together give an indication of the health of the liver. The liver can be damaged by hepatitis, alcohol and other drugs, being overweight, and by HIV antiviral drugs directly; so it is important to keep a watch on liver function.

Kidney function   Kidney function is measured by the levels of ‘waste’ products such as urea and creatinine.  Some HIV antiviral drugs can affect the levels of these waste products because they compete with them for excretion in the kidney.  Some HIV antiviral drugs may have an impact on kidney function.  Kidney function is checked in two ways: in a blood test and in a urine test.  Kidneys that are not functioning well may allow protein from the blood stream to filter into urine.   Your doctor may request a urine test for protein/creatinine ratio.

Platelet count  Platelets are important in helping your blood clot in response to a cut or wound. HIV itself and some HIV antiviral drugs can decrease the platelet count.

Haemoglobin and Haematocrit  Haemoglobin measures the levels of the key protein which transports oxygen around the body. Haematocrit is a measure of the proportion of blood that is red blood cells. Low haemoglobin levels or a low haematocrit can be an indicator of anaemia: a known side-effect of some of the older HIV antiviral drugs.

Resistance testing  Resistance testing can be done using a number of different tests which aim to establish whether the virus being tested has evolved in response to antiviral treatment, meaning that if HIV has been exposed to insufficient drug to stop it reproducing, it may have mutated so that it can overcome the level of drug to which it is exposed. If it has, this information will help determine which treatments are likely to be most effective. This test can only be performed if you have a detectable viral load.

The current treatment guidelines suggest that this test should be performed:

• prior to commencing treatments
• to assist in correctly selecting treatments when considering changing treatments
• if there is indication of viral load change during treatment
• within 4 weeks after discontinuing or stopping treatments

Abacavir Hypersensitivity  This test is a genetic test used to determine the likelihood of a serious, possibly fatal reaction to the drug Abacavir.  It is requested by by your doctor prior to commencing Abacavir.

Therapeutic drug monitoring (TDM)  Therapeutic drug monitoring (TDM) is used to help individualise anti-HIV therapy by measuring the amount of drug in an individual’s blood (plasma) or cerebral (spinal) fluid. This is important because different people absorb, process, and eliminate drugs at different rates, and blood and cerebral fluid levels may vary considerably among individuals taking the same doses of the same medications. Ideally, the lowest plasma drug concentration between doses should still be high enough to inhibit HIV, but the highest concentration should not cause intolerable side-effects.

Some, but not all, studies have shown that using TDM to guide treatment decisions increases the chance of successful viral suppression and can assist in minimising side-effects; however, drug level monitoring is not appropriate for all anti-HIV drugs.