#falsenegative

Researchers develop model to estimate false-negative rate for COVID-19 tests

Credit: Unsplash/CC0 Public Domain Even with more than 1.5 million Americans receiving a COVID vaccine each day, officials estimate it will take many more months before enough people are protected from the deadly virus. Until then, and potentially beyond, experts agree that opening up schools, restaurants and other public places as safely as possible will rely on widespread testing for…

“Congratulations, you have a yeast infection!” were the last words I was expecting to hear from my doctor.

Before the "diagnosis"

Two weeks earlier, after several months of trying to get pregnant following a miscarriage, we finally got a positive home pregnancy test. But a follow-up test at the doctor’s office the next day was negative. This was days before my period was due, I should note...I am not a patient woman. The nurse insisted that there must have been something wrong with the home test. I was devastated. However, after browsing some online pregnancy forums I became more optimistic. Apparently, this type of thing happens somewhat often. The nurse naturally disagreed, but after my pestering questions and insistence wore her down she begrudgingly booked me a future appointment, noting I could cancel it when I got my period. No period came, and at the scheduled date I excitedly peed in yet another cup. I met with the doctor while we awaited the results, and to kill time she asked me if anything felt different. I hadn’t really noticed any typical pregnancy symptoms, but I did mention that having sex had been a bit uncomfortable lately. “Maybe related to early pregnancy hormones?!” At this point I was looking for signs anywhere I could find them. Just to be safe, the doctor collected a swab sample and went to have a look at it herself. About 5 minutes later she came back into the room beaming from ear to ear. This is it, I thought. The results are back. I’m pregnant!

Well, maybe...

Basically the opposite of an infection, yeast is also responsible for making bread fluffy and delicious! “It’s beautiful, the most perfect specimen I’ve ever seen!” she exclaimed.  Of yeast. Stupid, stupid yeast. She must have seen my face fall because immediately she explained “we're still waiting for the test results, but this is actually great news! A yeast infection is a sign that you may very well be pregnant.” Ummm...what? I guess it was time for that "learning something new every day." During early pregnancy, the hormonal landscape of a woman’s body transforms dramatically. The vagina is home to a diverse array of microbial life, mostly consisting of some mix of bacteria and yeast in normal conditions. However, pregnancy causes shifts in the microbial community (see! pregnancy hormones?!). This can lead some species that were once backseat drivers to take the wheel. Sometimes, potentially harmful bacteria can take over, such as Strep B. But more frequently, the balance tips in favor of innocuous yeast. The species is usually C. Albicans, but can be others as well. Yeast infections in early pregnancy are extremely common. Candida species tend to colonize the vagina of about 20% of non-pregnant women and 30% of pregnant women. Another strange "side-effect" is that if you're pregnant, you may be less likely to know you have an infection. A greater proportion of pregnant women don’t have symptoms.

A baby, a bug, or both?

A: A false positive is a rather rare occurrence indeed. The two most common causes of, or explanations for, a false positive are 1) Use of hCG-containing fertility drugs (clomid is not one of them) and 2) improper use of test or failure to observe guidelines on test interpretation. With regard to the latter explanation, a false positive associated with improper use is typically caused by an attempt to interpret a test result after the given "reaction time" of a test. With most tests, you should not read a result after the five or ten minute time interval specified by the manufacturer. Hardly anything (besides fertility drugs) can interfere with a preg test result, so a true false positive is not a common occurrence. As for a false negative, these may be more common due to the issues such as hCG production, rates of hCG increase, and testing tips. If you do elect to test early, we always advise to take follow-up tests to account for various variables that may postpone or slightly delay a first positive result. Such variables include date of implantation, concentration of hCG in a given urine sample, specific rate of hCG increase (depends, in some cases, on where in the womb the fetus implants). Again, please view our testing tips to ensure maximum accuracy!