(Reports) What does a negative result mean?

This is a question that comes up sometimes when clients are hoping to be certain the tank is parasite- or pathogen-free.

On one level the answer is straightforward – we found no evidence of any DNA matching the organism of interest (pathogen, etc). Assuming that we got enough high-quality data from your sample, we expect that if the known parasites or pathogens were present at typical levels, we would have detected them.

(If for some reason we didn’t get enough data from your sample to be confident about this conclusion, we’ll email to discuss – and probably re-run your sample to be sure).

It’s important to recognize that all tests have a limit of detection, so parasites present at a low enough level might be missed. This is true for any testing method. With DNA sequencing, the limit of detection depends on the number of sequences analyzed. For our tests, we analyze thousands of sequences from every client’s sample to maximize the sensitivity of our tests for detecting rare members of the community.

Like any diagnostic test we can’t prove the target is absent, only that we found no evidence of its presence, and that our test would have detected it if it were present at meaningful levels.