Mgen testing uses an FDA-cleared NAAT (nucleic acid amplification test) on a urine sample or a swab to detect Mycoplasma genitalium's genetic material. Because macrolide resistance is now common, current guidance is to pair detection with a macrolide-resistance assay where available so treatment can be matched to the strain — a step unique to this infection.
rising — guides therapy
doxy → moxifloxacin
| Item | Value |
|---|---|
| US adults infected | ~1–2% |
| Azithromycin resistance | ~50% — rising — guides therapy |
| Often | no symptoms |
| Treatment | resistance-guided — doxy → moxifloxacin |
How Mgen is tested
Mycoplasma genitalium is a tiny bacterium that lacks a cell wall, which is why penicillins and cephalosporins — the beta-lactam antibiotics that kill many other bugs — simply have nothing to attack CDC, 2021. That same trait makes it slow and impractical to grow in a lab, so diagnosis relies entirely on molecular testing rather than old-fashioned culture. If you want the full background on the organism itself, see our overview of mycoplasma genitalium.
The test that matters is a NAAT, which amplifies and detects the bacterium's DNA or RNA from your sample. It's far more sensitive than older methods because it can find genetic material even when only a small number of organisms are present. A standard STI panel usually does not include Mgen — you have to order it specifically, which is one reason the infection is often missed in people with stubborn symptoms.
Which sample is used
The FDA-cleared NAAT runs on several sample types, so collection can be matched to your anatomy and comfort. Options include a first-catch urine sample, a urethral or penile-meatal swab, an endocervical swab, or a self-collected vaginal swab. Self-collected vaginal swabs perform well, which means many people can collect their own sample without a pelvic exam.
The other half of Mgen testing is what sets it apart: a macrolide-resistance assay. This looks for the specific genetic mutations that make the bacterium shrug off azithromycin. The catch is honest and important — resistance testing should guide therapy, but a commercially available resistance assay is not yet on the market in the US. In practice that means many labs report only whether Mgen is present, and your clinician chooses treatment around the strong likelihood of resistance.
When to test after exposure
NAATs detect the organism itself, not your immune response, so they can turn positive relatively soon after exposure once the bacterial load is detectable. There's no single official window for Mgen the way there is for some infections, so testing is generally driven by symptoms — persistent urethritis or cervicitis — rather than a fixed countdown. If you're testing because of a known exposure, our guide on the general timing of when to test after exposure explains why testing too early can miss an infection that hasn't built up yet.
Who should get screened
There is no recommendation to screen asymptomatic people for Mgen — routine testing of those without symptoms is not advised. The organism is common, often causes no symptoms at all, and testing everyone would lead to a lot of treatment that may do more harm than good given the resistance picture.
Instead, testing is targeted at the people in whom it actually changes management:
- Men with recurrent or persistent non-gonococcal urethritis (NGU) — urethral inflammation that comes back or never fully clears after treatment for chlamydia and gonorrhea.
- Women with recurrent cervicitis — inflammation of the cervix that persists despite treatment for the usual causes.
- People whose urethritis or cervicitis hasn't responded to standard first-line therapy, where an unrecognized Mgen infection is a leading suspect.
Pelvic inflammatory disease and partners of diagnosed patients may also warrant testing depending on your clinician's judgment, but the common thread is symptoms or a strong clinical reason — not curiosity-driven screening.
Getting tested: the visit, at-home kits, and cost
Testing is far less of an ordeal than people fear. Most diagnoses come from a simple sample — a urine cup, a self-collected swab, or a quick exam — with results usually back in a few days. There's no needle for the test itself and, in many cases, no pelvic or genital exam if you can self-collect.
In a clinic, you'll give a sample, and the lab runs the NAAT. At-home and mail-in options exist too, though you should confirm a kit actually tests for Mgen specifically — many standard panels don't. Cost varies: testing is free or low-cost at health departments, Planned Parenthood, and Title X clinics, while mail-in services price it per test. If you're weighing options, you can get tested through several routes, and it helps to compare testing providers before you buy, since coverage of Mgen and resistance markers differs by company.
Reading your results
A NAAT result is reported as detected (positive) or not detected (negative). A positive means the bacterium's genetic material was found in your sample — it does not, by itself, tell you which antibiotic will work. That's exactly why the resistance assay matters: it's the difference between knowing you have Mgen and knowing how to cure it.
A negative result in someone with ongoing symptoms doesn't always close the case. Sample quality, timing, and other causes of urethritis or cervicitis all factor in, so your clinician interprets the result alongside your exam and history rather than treating the number in isolation.
If your Mgen test is positive
A positive result calls for resistance-guided treatment, not a single dose of the old standby. Because macrolide-resistance mutations now exceed half of cases in many areas — over 62% in one US STI clinic — the once-routine single azithromycin dose frequently fails NYSDOH/JH. The current approach typically starts with doxycycline to lower the bacterial load, then follows with azithromycin if the strain is macrolide-susceptible or moxifloxacin if it's resistant. For the full regimen and what to expect, see our page on mgen treatment.
Whatever you're prescribed, finish all of it even once you feel better — stopping early is part of how resistance spreads. Ask your clinician whether your partner needs treating too, so you don't pass the infection back and forth. A diagnosis here is common and treatable; clinics handle it daily, and it says nothing about you as a person.
When to see a clinician
See a clinician if you have urethral discharge or burning, pain with urination, abnormal vaginal discharge, bleeding between periods or after sex, or pelvic pain — especially if symptoms persist after you've already been treated for chlamydia or gonorrhea. Recurrent symptoms that don't clear are the classic signal that Mgen should be on the table.
Beyond the individual visit, this organism is a public-health concern in its own right; it's worth understanding why health agencies around the world are worried about mycoplasma genitalium and its growing resistance. Using condoms every time lowers the risk of the sexually transmitted infections in this family, and routine testing catches the ones that cause no symptoms.