Rapid diagnostic tests are high quality, low-cost and easy-to-perform tests for use in resource-poor settings. Mainly used for HIV or malaria, they are frequently in the news with the development of rapid tests for Zika virus. We talked with Bill Rodriguez, chief medical officer at FIND, a non-profit organization that helps the development and delivery of diagnostic tests for poverty-related diseases.
ME e-mag: When were the rapid tests first developed?
Bill Rodriguez: The history goes back to the 1960s, but really the first good commercial rapid test was the pregnancy test in the 1980s. Next, it was the HIV test in the 1990s. There were always small numbers of tests and actually a lot of them were for the veterinary industry. But the use of rapid tests for human diagnosis—other than pregnancy tests—really started taking off in the early ’90s. And then, for the past 15 years there has been an explosion driven a lot by HIV and by malaria.
ME e-mag: Now you can even find rapid tests for Zika virus.
Bill Rodriguez: For Zika virus, there are a few rapid tests that have been approved in Brazil and in the United States. But they are not generally available because they have been used on a very local basis and they have been manufactured by very small companies. There are a number of large companies that are right now developing rapid tests for Zika and are likely to be approved this year. By, let’s say, 12 months from now, there should be a number of Zika rapid tests on the market.
ME e-mag: What is the main purpose of the rapid tests?
Bill Rodriguez: In general, the rapid tests are used for screening, meaning they’re used in a population of people that may or may not have symptoms. So they’re used to identify who should go and get a confirmatory test in a higher-level health facility.
But there are exceptions. For HIV and malaria, the rapid tests are actually used for diagnosing. Once you have a positive test, you receive treatment. For many other diseases, including Zika or sleeping sickness, you often need to go get a confirmatory test that is more specific, that has a better performance, but is much more complicated to operate.
ME e-mag: Why is it different for HIV and malaria?
Bill Rodriguez: For HIV, there has been a lot of research to develop very high-performing tests, and usually you run two rapid tests in parallel so when you get two rapid tests that are both positive for HIV, then that’s considered sufficiently reliable to start the treatment.
For malaria, people would just do one rapid test and usually that’s enough for most foundations and programs to start malaria treatment. But malaria rapid tests have not been around for quite as long as HIV tests and they’re not as high performing, although they’re very good, so it still depends on where you are in the world. Some settings won’t start a malaria treatment just on the basis of a rapid test. But in general it’s true that it’s all you need.
ME e-mag: How do you prove that those tests are reliable?
Bill Rodriguez: Let’s take malaria as an example. In general, you run a clinical trial where you enroll a few thousands of patients with fever from a variety of countries in the world. Then you run a rapid test and at the same time you run the gold standard test which at the time was a blood smear under microscope or a PCR test. And you look at the performance of the rapid test compared to the performance of the gold standard test.
In addition, you’re also looking at how easy is it to run the rapid test against how hard is it to run the gold standard test. Usually, the combination of performance and simplicity is the right data to then present to the World Health Organization (WHO) or a national policy body who are going to say if they recommend their use or not.
ME e-mag: How does a rapid test work?
Bill Rodriguez: For the test itself, you’re looking for some specific biomarkers from the disease. For malaria it is a protein that is produced by the malaria parasite. To use the tests, it is usually from a finger stick of blood that you put on the sample port, and then you wait ten to 15 minutes. It’s very easy to use.
ME e-mag: Will we see more and more rapid tests in the future?
Bill Rodriguez: Yes. The technologies are now advancing really far so there will be more and more interest in using rapid tests for diseases like Zika, dengue or Leishmaniasis. We’ll see probably a wave of new rapid tests in the next three to five years. Unfortunately there will be some diseases for which rapid tests just are not either sensitive enough, or because of the biology of the disease there’s no target, no biomarker. That’s true for diseases like tuberculosis.
ME e-mag: Can you also do combinations of tests?
Bill Rodriguez: Absolutely. For instance, right now we are working with a Korean company on a test that combines malaria with sleeping sickness, because they overlap in a part of Africa where they are common, so it is very useful to have a single test to evaluate the patient for the two diseases at the same time. You’ll be able to tell which one they have.
ME e-mag: What are the other applications for rapid tests?
Bill Rodriguez: They are definitely used in veterinary medicine. For diseases that cattle get, rapid tests are very useful because the farmers and ranchers have limited resources to do testing. They are also used to detect drugs abuse (usually urine tests), or on pregnant women to evaluate a disease called pre-eclampsia. And they’re probably going to be used for measuring drug resistance or drug levels for antibiotics.