Testing of gut bacteria is sometimes advocated to improve gut health. Test the bacteria, change diet or supplements, then test again to see if there has been improvement.

    But what if the tests are unreliable?

    In a recent study, researchers took gut bacteria from a pool created to provide identical samples (unlike samples from stool, where different parts of the stool may have different species present). They sent three separate submissions to each of seven direct-to-consumer laboratories. They did not inform the facilities that they were conducting the study.

    Their results were recently published in Nature. Even though the bacteria in the samples were identical, the laboratories got different results. The article explains how differences in technique from lab to lab can influence this. But some labs reported that the specimen was from a healthy microbiome, while others reported various issues.

    Even more troubling, some of the seven labs did not get the same results on the three identical samples. Internal consistency is one of the hallmarks of a good laboratory.

    The study of the microbiome is in its early days. Five years from now, the tests may be more reliable. Right now, many clinicians believe stool testing is not reliable enough to guide treatment.

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