Positive test and negative test

Posted by kwb1970 @kwb1970, Dec 24, 2018

I’ve recently been diagnosed with MAI by a new doctor. About a year ago I had a positive culture, and immediately went back for a second culture. My second test was negative. So for the past year my doctor has been trying to rule out MAC, saying I has a 50/50 chance since one test was negative. This doctor moved, and I met with a new doctor and he said I definitely have MAC. Has anyone ever heard of a false positive test?

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@kwb1970 I have heard of false positives by reading all the info on the internet. I believe 2 sputum cultures, done relatively close together, with colony count and susceptability testing done (very important) produces the most accurate diagnosis. Some labs our docs use (like mine) do not have that kind of in-depth lab facilities and will do an AFB (Acid Fast Bacteria) test only and treat with the outcome of that. It can be overwhelming to hear of and learn about the many faces of our diseases. I've learned so much and you can too by looking over the older posts in this group and reading on the internet. Hugs, best of luck and good health to you!


Yes, it happened to my husband just this year. He had 3 sputum cultures (taken at one-day intervals) tested by our state department of health (this is where our clinic sends them to be grown out for roughly 6 weeks.) Only one came back positive, and the doc explained that since MAC is everywhere in the environment, false positives can occur if the sample is accidentally contaminated, either by the patient or the lab. He ONLY treats if 1)multiple cultures are positive and 2) you are symptomatic. On the other hand, ALL 3 of my cultures were positive, and were then sent to the NJH labs for sensitivity testing to determine the best combination of antibiotics to treat my infection. Our pulmonologist does not treat MAC based on AFB results – he doesn't consider them a reliable diagnostic. He does, however, use for follow-up testing during treatment – then if the AFB shows positive, they retest at the state lab to confirm a continuing active infection.

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