Many people living with HIV ask me questions regarding their viral load. They often ask: Is my viral load normal? Is it too high? What do terms like "detectable," "undetectable," and "not quantifiable" actually mean?
Before I can answer those questions, let's discuss a few basic principles. (For this article, when I refer to HIV, I am talking about HIV-1, by far the most common strain of HIV worldwide.)
HIV Viral Load: What You Need to Know
First, what is "viral load"? Viral load is the amount of HIV RNA -- HIV's genetic code -- in the blood plasma. It cannot be measured directly, but tests have been developed that amplify the amount of HIV present in a person's blood sample so we can see or measure it. We refer to this amount as copies of HIV per milliliter (copies/mL) of blood. Most of the viral load tests we use today in the U.S. can detect a copy number as low as 20 copies/mL and as high as 10 million copies/mL. ("Viral load" and "copy number" are used interchangeably.)
When someone is first infected, their HIV copy number can be in the millions. When the immune system mounts a defense against the virus, the viral load falls, even if a person hasn't yet started treatment. Where it settles down to is different for everyone: Some people will continue to have a viral load over 100,000, while others can naturally develop an undetectable HIV viral load, although this is very rare.
The term "undetectable" usually means an HIV viral load of less than 20 copies/mL, the lower limit that most tests are capable of detecting. A viral load of over 100,000 is considered high.
How HIV Treatment Affects Your Viral Load
What I have just discussed relates to people who are living with HIV and have not started HIV treatment. When someone starts HIV treatment, their viral load falls significantly. Within a few days, HIV stops replicating. Within 3 to 6 months, their viral load usually becomes undetectable (less than 20 copies/mL) -- even if it was in the hundreds of thousands when they started treatment.
An undetectable viral load does not mean that the virus is gone from the body. But as long as one continues to take HIV meds as prescribed, their viral load can remain undetectable indefinitely. Recent studies have shown that when the viral load is undetectable, it is virtually impossible for someone living with HIV to transmit the virus to someone else through sex. This is referred to as undetectable = untransmittable, or U=U.
If someone stops taking HIV medications when they have an undetectable viral load, the viral load will again become detectable within a few days. After a few weeks of no HIV treatment, the viral load can return to levels seen before starting treatment. Restarting HIV meds should result in an undetectable viral load again -- that is, assuming the virus hasn't become resistant to any of those medications in the meantime.
Finally, if someone is taking HIV medications and their viral load falls, but never becomes undetectable (or increases), this could indicate that HIV has become resistant to the person's HIV medications. If available, an HIV resistance test will help determine what HIV medications need to be changed to get the viral load to an undetectable level.
So, Is There Such a Thing as a "Normal" Viral Load?
When laboratory results like a cholesterol level or white blood cell count come back, we often hear (or hope to hear) that they are "normal" or "in the normal range." However, with HIV, defining a "normal" viral load is difficult. For one thing, having a detectable HIV viral load is itself not a normal lab test result, given that the vast majority of people in the world are not living with HIV.
In addition, people who are living with HIV but who are not yet on HIV treatment will not usually have the same viral load level as people who are living with HIV and are on treatment. Among HIV-positive people, viral load can range from just a few copies to several hundred thousand, or even millions.
Complicating things further is that the amount of viral load usually doesn't correlate with how people may feel, even though higher viral loads are a marker of faster progression of HIV infection. And regardless of where their viral load was before they started treatment, once people start and stay on HIV medications, the viral load should become undetectable. Thus, I would be reluctant to put a number, or even a range, on what we should define as a "normal" viral load.
Viral Load Test Quirks: "Not Quantifiable," "Blips"
HIV viral load assays have evolved over time and gotten more sensitive. Although current tests in the U.S. tend to detect viral load amounts as low as 20 copies/mL, slightly older tests can't detect amounts below 50 copies/mL -- and there are still some tests in use that can't go below 200 copies/mL.
Up until a few years ago, the test result only would say "undetectable," meaning HIV couldn't be detected or reported below the lowest level of detection of that specific test. But because the term itself is vague and tests have become more sensitive, assay companies are now allowed to say a more descriptive phrase: "detectable, but not quantifiable" below the lower level of detection.
The problem with this new phrase is that it can raise anxiety unnecessarily. A viral load test can now determine if no viral load is detectable at all (i.e., undetectable), or that viral load is detected but can't actually be counted, because at such low levels the test is imprecise, so you only can get a yes or no answer regarding whether a viral load is present (i.e., detectable, but not quantifiable). This has caused significant concern among providers and the HIV community that people will perceive "detectable, but not quantifiable" to mean that a person's HIV treatment is not working. The good news is that in most cases, an extremely low viral load (also called low-level viremia) does not result in treatment failure.
You may also hear about an issue called "blipping." That is the term we sometimes use when a person's viral load has been undetectable for several months (or even years), and then suddenly becomes detectable at some copy number between 20 and 200.
There are two potential causes of a viral load blip:
- Usually, this is related to a normal amount of variation between tests, and the person's viral load will return to undetectable on the next test.
- Sometimes, a blip can reflect low levels of HIV replication even while a person is on treatment. If a person's viral load continues to increase over time -- i.e., to a level above 200 -- even though they are taking HIV medications as prescribed, they should repeat their viral load test. If the increase is confirmed, this could indicate that their current HIV medications are not working, and they should talk with their health care provider for additional workup, testing, and next steps, which may include selecting a new, more effective regimen.