The Cost-Effectiveness of Testing HIV for Genetic Signs of Drug Resistance as a Guide to the Choice of Therapy

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The summary below is from the full report titled "Use of Genotypic Resistance Testing To Guide HIV Therapy: Clinical Impact and Cost-Effectiveness." It is in the 20 March 2001 issue of Annals of Internal Medicine (volume 134, pages 440-450). The authors are MC Weinstein, SJ Goldie, E Losina, CJ Cohen, JD Baxter, H Zhang, AD Kimmel, and KA Freedberg.

What is the problem and what is known about it so far?

Human immunodeficiency virus (HIV) interferes with the ability to fight infections. Therapy with combinations of anti-HIV drugs can reduce the amount of the virus in the blood and improve patient outcomes. Unfortunately, the virus can become resistant to the drugs, and the patient must then change to another combination. It is now possible to test the genes of the virus directly for signs of resistance to particular drugs (genotypic resistance testing). It is unknown whether the cost of these tests is worth the benefit.

Why did the researchers do this particular study?

To learn whether using genotypic resistance testing to guide the choice of anti-HIV drugs is worth the benefit.

Who was studied?

The researchers used computers to simulate what would happen to a hypothetical "virtual" group of patients with HIV infection.

How was the study done?

Using published data from previous studies, the researchers estimated the effect of using genotypic resistance testing in addition to doctors' judgment to guide the choice of anti-HIV drugs. They looked at 1) patients beginning anti-HIV drugs for the first time [primary resistance testing] and 2) patients in whom the first anti-HIV drug regimen had failed (secondary resistance testing). The researchers then explored what would happen over time depending on whether genotypic resistance testing was used, and they calculated how much each strategy would cost society for a given amount of benefit. Benefit was measured in quality-adjusted life-years (QALYs), a unit of measure that considers not only how long a person lives but also his or her quality of life during that time.

What did the researchers find?

If only about 4 of every 100 patients beginning their first anti-HIV drugs were infected with resistant virus, primary genotypic resistance testing would cost $69,000 per QALY gained. If 20 of every 100 had resistant virus, then primary resistance testing would cost $22,300 per QALY gained. Secondary resistance testing was estimated to cost about $17,000 per QALY gained. On the basis of these findings, and compared with many other accepted therapies, genotypic resistance testing can be considered cost-effective.

What were the limitations of the study?

This study was a computer simulation, so we cannot be sure what the results would be with actual patients.

What are the implications of the study?

Genotypic resistance testing of patients in whom an anti-HIV drug regimen has failed appears to be cost-effective. Genotypic resistance testing of patients beginning their first anti-HIV drug regimen may be cost-effective if the suspicion of resistance is high.