How reliable are genetic tests?

Posted 7 years ago by Andreas Obermair

Increasingly, genetic tests can be ordered by the general public; they are called direct-to-consumer tests. Because they market to large number of consumers and because they don’t need to undergo the same quality tests, they can be ordered by consumers online.

These tests, such as 23andme or ancestry determine your ancestry and even whether you carry a predisposition for a large number of medical conditions in the future. Many of us want to know what the future brings. Hence, these tests have become bestsellers.

However, how scientific are these tests? If I would order such a test online, how reliable is it?

I will never forget the case of a middle-aged woman who saw me to assess an ovarian cyst. The cyst did not look suspicious. However, at the end of the consultation, my patient mentioned that she had done the 23ANDme test. I reviewed the results and it stated that the patient tested positive for BRCA2.

BRCA is a gene, when mutated increases the risk of breast and ovarian cancer significantly. The lifetime risk of ovarian cancer in the general population is 1.3%. By contrast, in carriers of BRCA, the risk developing ovarian cancer is between 40% and 60%.

Until then, I was not even aware that this test offered a BRCA test. I certainly got alarmed. Here I saw a patient with an ovarian cyst that at first sight looks unsuspicious but she has a BRCA mutation. Based on the mutation alone, I had to consider this patient high-risk for ovarian cancer.

I picked up the phone to discuss the case with a colleague who also is knowledgeable in this area. He confirmed that the test result needs to be taken serious. However, to be on the safe side and in order to avoid over-treating the patient, we agreed to repeat the test through scientific avenues.

We were both completely taken by surprise when the test result did not confirm BRCA. It virtually confirmed that the patient received a false positive test result through 23ANDme.

Two months later, the cyst has disappeared and no surgery was required. The patient remains well.

A study published in March 2018 has shown that up to 40% of direct-to-consumer tests are false positive. The percentage of tests that miss a diagnosis (false negative tests) is unknown.

The upshot of this story is that …

1. Direct-to-consumer tests are not reliable to test for cancer risk. They don’t undergo the same scrutiny that tests have to go through that are ordered by your doctor.
2. I expect that direct-to-consumer tests not only show false positive results but also have false negative results, where the cancer mutation is missed.
3. In my practice, we only offer tests to check for cancer genes. They fulfill very high scientific standards, undergo ruthless quality checks and are accurate.

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