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Why did i need two types of STI Tests?

My doctor tested me for trich by taking a swab from my vagina, and then tested my urine for chlamydia. I don’t understand why I needed two tests. My friend was tested for a bunch of STIs and said they used a swab for her to test for trich, chlamydia, and gonorrhea.

Expert answer

There are several ways to test for trichomonas (“trich”) and different providers may use different methods. Trichomonas is a motile one-cell parasite which can be viewed in a “wet preparation” of a vaginal swab on a slide under the microscope by the clinician. It is diagnosed by its motion on the slide under the magnification of the microscope.

Another way to detect it is to take a vaginal swab and send it to the laboratory for culture, which is a method to grow it; it is a little more sensitive than viewing it directly on a wet prep.

Recently, there is a new molecular test that is much more sensitive (more accurate) than “wet prep” or culture that amplifies the DNA from the swab or urine or a liquid PAP specimen. This is much like PCR or polymerase chain reaction that is powerful method for diagnosing infections. Tests for chlamydia, gonorrhea, and trichomonas can all be performed from a single swab or from urine using the new molecular method. Your doctor may have needed a separate swab for trichomonas if she/he was using a wet prep or culture method. The number of swabs (or use of urine) all depends on the type test the doctor is using.

–Charlotte A. Gaydos, DrPH, MPH, MS