How Trichomoniasis Is Diagnosed

trichomoniasis diagnosis
© Verywell, 2018 

Trichomoniasis is caused by the parasite Trichomonas vaginalis. For many years, the primary way of diagnosing trichomoniasis was to use a microscope to look for the parasite in a vaginal swab. However, STD testing technology has improved greatly in the last few years. Now, trichomoniasis is more often looked for using DNA amplification or rapid testing techniques. Such techniques can find the parasites even when very few are present in a urine or other sample.

Testing for trichomoniasis is important because many infected people have no symptoms. That means that you can't rely on the presence or absence of symptoms to know if you have this (or other) STDs. Many people can remain asymptomatic for trichomoniasis for years. However, even when no symptoms are present, trichomoniasis can still cause health problems or infect a partner.

At-Home Testing

Several companies have begun to offer online or at-home testing for various STDs, including trichomoniasis. The best of these tests are the same tests that would be provided in your doctor's office. The only difference is that for a home test, you are the one who takes the sample rather than your doctor.

Samples for at-home trichomoniasis tests can include urine, vaginal swabs, and rectal swabs. (Rectal swabs are used to detect STDs passed during anal sex.) These samples are then mailed to or dropped off at, a lab for testing.

At-home trichomoniasis testing can be a good option for people who are uncomfortable talking to their doctors about STDs. However, at-home tests are not for everyone. At-home tests are not covered by insurance, and they can be quite expensive. In addition, some people aren't comfortable taking their own samples or preparing them to send to a lab.

If you do think an at-home test is a right choice for you, make certain the samples are sent to be processed at a certified testing laboratory such as Quest or LabCorp. This information should be available wherever you purchase your test.  

Note: There are no "instant" home tests for trichomoniasis.

Labs and Tests 

Microscope Analysis

In women, the most common way to diagnose trichomoniasis is to use a microscope to examine a vaginal sample. The Trichomonas parasite is very distinctive looking, and it is easy to identify.

However, there are problems with this type of testing. It is much less sensitive than other types of tests. How well the tests work is also very dependent on how samples are collected and treated. On the other hand, microscopic examination of a vaginal sample is very cheap and can be done in the office setting. 

Culture Analysis

Another way to test for trichomoniasis is to use culture techniques. These techniques attempt to grow trichomonas from collected samples. They can be very finicky and difficult to use.

For culture to be successful, it is very important to collect samples properly and avoid the risk of contamination. While culture can be an inexpensive way to detect trichomoniasis, it requires trained personnel.

It is also less sensitive than many other testing techniques.

Molecular Testing

These days, molecular tests are far more likely to be used to detect trichomoniasis than microscopes. Molecular tests for trichomoniasis work in several different ways. There are several types of these tests.

Perhaps the most common are nucleic amplification tests. These look for small amounts of T. vaginalis DNA in urine, vaginal, urethral, or rectal samples. They are more sensitive than many other molecular tests because they are designed to amplify the signal of even small amounts of DNA.

Other molecular tests exist as well.

Rapid tests can use antibodies to detect the presence of trichomonas in various samples. These tests are more expensive than options like culture or microscopy, but they are also much easier. They often don't require special handling of samples, and results can be available quite quickly.

There are additional specialized tests that look for trichomonas DNA but do not amplify it. These tests are less sensitive than amplification tests. However, they are faster and less expensive. 

Differential Diagnoses

Many STDs have similar symptoms or no symptoms at all. As such, it's very difficult to diagnose these conditions without diagnostic testing. That's why, in general, if you're going to be tested for one STD, you'll be tested for multiple STDs. In particular, the symptoms of trichomoniasis, chlamydia, and gonorrhea are similar enough that you will usually be tested for all three conditions at once.

Another reason that people are generally tested for multiple STDs at once is that these conditions often occur in groups. In communities where STDs are common, it is not unusual for people to be infected with multiple diseases. As treatments are different for each of the STDs, it's very important to use testing to identify precisely what infections are present. Only then can appropriate treatment be prescribed.

In general, when you are tested for trichomonas you will simply receive a positive or negative result. It is possible, however, for the tests to be incorrect. Therefore, if you have symptoms that cannot be explained by another positive test, your doctor may recommend a second round of testing. If symptoms recur after you've been treated, additional testing may also be indicated. 

Sources:

Hobbs MM, Seña AC. Modern diagnosis of Trichomonas vaginalis infection. Sex Transm Infect. 2013 Sep;89(6):434-8. 

Meites E, Gaydos CA, Hobbs MM, Kissinger P, Nyirjesy P, Schwebke JR, Secor WE, Sobel JD, Workowski KA. A Review of Evidence-Based Care of Symptomatic Trichomoniasis and Asymptomatic Trichomonas vaginalis Infections. Clin Infect Dis. 2015 Dec 15;61 Suppl 8:S837-48.

Šoba B, Skvarč M, Matičič M. Trichomoniasis: a brief review of diagnostic methods and our experience with real-time PCR for detecting infection. Acta Dermatovenerol Alp Pannonica Adriat. 2015;24(1):7-10.