The Bay Area Reporter - November 23, 1998
Bill Snow, ACT UP/Golden Gate Writers Pool

What is viral load?

The currently available viral load tests measure virus in the blood by one of two methods: PCR by Roche or branch DNA (bDNA) by Chiron. The two methods are very different, but most researchers agree that they are equally good and reliable. The Food and Drug Administration (FDA) approved the Roche medium-sensitive test (which measures down to 500 copies/mL) some time ago, but in the last few months it has commonly become possible to measure viral load down to 50 copies/mL, with new ultra-sensitive Roche and Chiron assays.

Either test has certain innate limitations. They don't distinguish between virus that can and cannot replicate, and there can be a great many "non-productive" viral particles in the blood, so two people with the same viral load count may have different levels of infectious virus. Since the test only measures virus in blood, more painstaking and unavailable analyses of tissue and other, protected compartments of the body, like testicles and brain, may have different amounts (and different mutations) of virus.

How reliable is it?

Finally, the test is based on a logarithmic scale, which means that each factor of 10 is an equal measurement (50 to 500 say, or 5,000 to 50,000, or even 50,000 to 500,000 are all equivalent differences!) Furthermore, the tests are accurate to about half a log, so two readings, with one being three times the other could be due solely to test variability. (Since one log equals 10 times, half a log is 10 to the one-half power, or the square root of 10, about 3.16 times.)

In addition, until now the two tests gave different results. Often the Roche PCR test gave higher results, which varied from individual to individual, but was generally double or more the viral load on the Chiron less-sensitive assays. This was a problem for someone who switched labs or assays, or who was getting viral load from more that one source, for example in a clinical trial and doctor's office.

Meanwhile practitioners talk about viral load levels as if they were uniform. They talk about "undetectable" virus, which has evolved from under 10,000 copies, to under 500, to under 50 - and down to five copies in some experimental settings. This chase toward exactitude is driven by the desire to actually approach viral eradication, which in turn is an effort to forestall activity that would lead to mutations. When Chiron labs tested a large number of samples that had been below 500 copies/mL on the older test, 50 to 60 percent were also below 50 copies, 30 percent were between 50 and 500 copies, and 10 to 20 percent were over 500. In addition, with their new version Chiron's raw numbers are much closer to the Roche PCR, so their new test either consciously or accidentally is much more in line with the approved PCR assay, which has been more widely used in a research setting.

Using the results

Those of us who can't get antivirals to reduce our viral load to these low levels are somewhat at the mercy of the chase toward undetectability. The new Chiron assay, version 3.0, is stated to give levels that are one to three times higher than the version two tests, which many of us, especially in Northern California, have been using as a standard.

Chiron has explained this in a "Dear Doctor" letter. Davies and Chiron labs have switched to the new sensitive assay, so most people who are not still undetectable should establish new baselines before assuming that a rise in their viral load it anything more than a result of the new assay. Doctors and patients need to stay calm and get used to higher numbers that may not mean anything has changed.

Payment

Last week many of us got an urgent e-mail from Brenda Lein at Project Inform because the Health Care Finance Administration (HCFA) has been holding a series of meetings over Medicare/Medicaid coverage of diagnostic and monitoring tests.

Essentially, HCFA proposed that a National Policy recommendation be made that Medicare covers only FDA-approved tests. What this means is that only the Roche PCR less sensitive test would be reimbursed. Currently states are given codes to cover HIV RNA monitoring and testing that they can use at their discretion, whereas the new policy would only reimburse for the older Roche test.

People who are following standard of care guidelines and using more sensitive HIV RNA monitoring tests (e.g., limit of detection 50) would no longer be able to use these tests or they would have to pay out of pocket if Medicare had been their source for reimbursement. Yet, even the Department of Health and Human Services guidelines are being revised to this standard. Although this is a cost-neutral issue, whether someone is using the Chiron, Roche, or any other more sensitive tests, they would no longer be covered.

For people who have been monitoring at labs that use technology other than the Roche PCR less sensitive tests, baselines would have to be redrawn if they have to switch. Some county labs have been trained and equipped to run the Chiron DNA tests, and county labs will have to covert to the Roche technology and retrain staff. This may cause some delays and will certainly have a cost impact on county labs not using the older version of the Roche technology. The companies and a number of prominent researchers have lined up against this recommendation, so it may be averted. The results will be reported in the Federal Register with an opportunity for public comment.

Certainly, we must pressure the companies developing these technologies to get their applications and data submitted to the FDA and then pressure the FDA to review these materials quickly. However, regardless of formal FDA approval, sensitive HIV RNA testing is considered optimal monitoring. It would be wrong for HCFA to deny the underinsured and uninsured access to these tests. It is not a cost issue. The more sensitive tests do not cost more than the less sensitive tests, so HCFA would save no money in creating this difficulty for people.
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Always watch for outdated information. This article first appeared in 1998. This material is designed to support, not replace, the relationship that exists between you and your doctor.

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