Trichomonas vaginalis

Trichomoniasis is the most common curable sexually transmitted infection worldwide, yet it is often left off the standard testing panels people assume cover everything. A urine test can tell you whether you carry it, even if you feel completely fine.

That matters because most infections cause no symptoms, particularly in men, so it spreads between partners for months without notice. Left untreated, it is linked to a higher risk of catching HIV and to complications in pregnancy.

What This Test Actually Detects

This test looks for Trichomonas vaginalis (the single-celled parasite behind trichomoniasis) or its genetic material in a urine sample. It detects the organism itself, rather than a substance your body makes the way a cholesterol or blood sugar test does. A positive result means the organism was found, which almost always reflects an active infection in the urinary or genital tract, while a negative result means none was detected.

The most accurate way to find the parasite is a molecular method called a nucleic acid amplification test, or NAAT, which copies and detects the organism's genetic material. Modern urine NAATs correctly identify about 95 out of 100 infected women and close to 100 out of 100 infected men, and they rarely flag someone who is not infected. One practical caveat: these tests are FDA-cleared for women but not for men, so a lab must validate its own protocol before running them on male samples. Older approaches, such as looking for moving parasites under a microscope, miss many infections and should not be relied on to rule it out.

Most Infections Are Silent

You cannot judge this infection by how you feel. Depending on the study and population, roughly 70 to 85% of infected women have no symptoms, and in one large U.S. survey most had none at all. In clinic studies the presence of genital symptoms did not track with who actually tested positive, and in men the infection goes unnoticed even more often. A test, rather than a symptom check, is the only reliable way to know your status.

HIV Risk

The strongest reason to take this infection seriously is its link to HIV, the virus that causes AIDS. In a pooled analysis of 11 studies in sub-Saharan Africa, women infected with the parasite were about 1.5 times as likely to later acquire HIV as uninfected women. The parasite damages the protective lining of the genital tract, which appears to make it easier for the virus to get in. Clearing the infection removes one avoidable source of that added risk.

Pregnancy Complications

In pregnancy, the infection is tied to several problems for the baby. One pooled analysis found roughly a 42% higher risk of premature birth, about a 41% higher risk of the water breaking early, and about a 51% higher risk of babies being smaller than expected for their stage. The size of the effect varies across studies, and a more recent meta-analysis put the increase in premature birth lower, closer to 27%. The evidence is most consistent for premature birth. Knowing your status early in pregnancy gives you time to treat the infection before these risks play out.

Cervical and Prostate Associations

Two other associations are worth knowing, though the evidence is weaker than for HIV and pregnancy. Across 35 observational studies, women with the infection had a little over twice the odds of cervical precancer or cancer. In men, some studies link the infection to enlarged prostate and prostate cancer, but these findings come from smaller observational work and are far from settled. Treat these as reasons for attention, not as proof that the infection causes cancer.

Why Urine Can Miss Infection in Women

A urine sample is convenient, but in women it is slightly less sensitive than a swab taken directly from the vagina. In pooled data, urine caught about 95 out of 100 infections versus 98 out of 100 for vaginal swabs. The gap is largely anatomy: only about three-quarters of women with a vaginal infection also carry the parasite in the urinary tract, so a urine sample can come back negative while a swab would be positive.

Two other things distort results. If very few parasites are present in the urine at the moment you void, the sample can fall below what the test can detect. And if a lab uses microscopy instead of a molecular test, a negative result is far less trustworthy, because microscopy misses a large share of true infections. A positive result, on the other hand, is highly reliable, because these tests rarely mistake something else for the parasite.

Why Retesting After Treatment Matters

For an infection, tracking over time means something specific: making sure it is truly gone and does not come back. Repeat and persistent infections are common, especially in women, and standard guidelines recommend retesting about three months after treatment rather than assuming a single course cured it. A major reason infections return is an untreated partner, who can pass the parasite right back.

A sensible rhythm is to test when you have a new or higher-risk exposure, treat if positive, and then retest at three months. If you are managing ongoing risk, folding this into an annual sexual health check keeps you from carrying a silent infection for long stretches.

What to Do With an Unexpected Result

A positive result should trigger a few coordinated steps rather than a single fix. Because sexually transmitted infections travel together, this is the moment to test for chlamydia, gonorrhea, HIV, and syphilis if you have not already, since coinfection is common. Make sure current partners are tested and treated at the same time, or the infection is likely to bounce back.

If you are a woman with genital symptoms but a negative urine result, do not consider the matter closed. A vaginal swab is more sensitive and can catch an infection the urine sample missed, so that is the logical next test. A clinician can help you match the right specimen and follow-up plan to your situation.