Mycoplasma Genitalium (MGen) Test: What You Need to Know

What Is Mycoplasma Genitalium?

Mycoplasma genitalium (often abbreviated MGen or MG) is a bacterium that infects the genital and urinary tract. It is spread through sexual contact and is classified as a sexually transmitted infection (STI). It is much less known than chlamydia or gonorrhea and is not included in most standard STI panels, so it is frequently missed unless specifically tested for.

MGen is unusual because it has no cell wall. That single feature explains a lot: it is hard to grow in a laboratory, so older culture methods never worked well, and drugs that target the bacterial cell wall do not apply to it. The organism attaches to the lining of the urethra, cervix, or rectum and can persist quietly for months, which helps it pass between partners who feel completely well.

MGen Symptoms

Many people with MGen have no symptoms at all. When symptoms do appear, they can include:

• Burning or pain when urinating (urethritis)
• Unusual discharge from the penis, vagina, or rectum
• Pelvic or testicular pain
• Vaginal bleeding between periods or after sex
• Inflammation of the cervix (cervicitis) or pelvic inflammatory disease (PID) in some cases

Because symptoms overlap with chlamydia and gonorrhea, testing is the only way to know which infection you have. A negative result for those two common infections does not clear MGen, which is why persistent symptoms deserve a closer look rather than a repeat of the same panel.

How MGen Testing Works

The recommended test is a nucleic acid amplification test (NAAT), which detects the bacterium's DNA. A sample can be collected by:

• First-catch urine, the preferred sample for men and people with a penis
• Vaginal, cervical, or rectal swab, depending on exposure and symptoms

NAAT is far more sensitive than older culture methods, which are not recommended for MGen. The test looks for genetic material rather than living bacteria, so it can still detect an infection that would never grow in a dish. Some labs also offer a resistance marker test alongside the NAAT, which checks for the mutation linked to macrolide resistance and helps a clinician choose an antibiotic that is more likely to work.

Window Period

Because it takes time for an infection to become detectable, testing too early can produce a false negative. A commonly used window is 2 to 4 weeks after potential exposure. If you test sooner and results are negative but symptoms persist, retest after the window has passed. If you have no symptoms and no known exposure, there is usually no need to test outside that window.

Why Testing Matters: Antibiotic Resistance

MGen is of growing concern because it readily develops resistance to antibiotics. The U.S. CDC has highlighted azithromycin resistance as a significant problem. This is why:

• You should not take leftover antibiotics without testing
• Resistance-guided treatment, using tests that detect resistance mutations, may be recommended
• A confirmed diagnosis guides the correct antibiotic choice

If you have persistent urethritis, cervicitis, or PID that has not responded to standard treatment, MGen testing is particularly important. Treating blind, without a confirmed organism, can expose you to side effects while leaving the infection in place.

Who Should Get Tested?

• Anyone with persistent urinary or genital symptoms after treatment for other STIs
• People diagnosed with urethritis, cervicitis, or PID
• Sexual partners of someone diagnosed with MGen
• Anyone who wants a comprehensive STI check that includes MGen

Partners matter here. Because MGen often causes no symptoms, an untreated partner can reinfect you after treatment, which is why public health guidance usually calls for testing and treating partners at the same time.

How to Get an MGen Test

Because MGen is not part of routine STI screening, you often need to request it specifically. Direct-access testing lets you order an MGen NAAT online and collect a urine sample or swab at a local lab, usually without a doctor's visit. Results typically return within 2 to 5 business days. Bring any recent antibiotic history to the collection site, since it can affect how the sample is interpreted.

How Much Does an MGen Test Cost?

Direct-access MGen NAAT testing commonly costs between about $75 and $200, depending on whether the order covers a single organism or a multi-pathogen panel. Bundled STI panels that add MGen to chlamydia, gonorrhea, and trichomonas often cost less than ordering each test on its own, while resistance-marker add-ons push the price higher. Insurance may cover the test when a clinician documents symptoms. For direct-access orders, confirm whether the collection fee is bundled into the quoted price so the figure you see is the figure you pay.

MGen vs Chlamydia and Gonorrhea

Mycoplasma genitalium causes symptoms that overlap heavily with chlamydia and gonorrhea, so the three are often tested together. The key differences are in testing and treatment.

Because routine panels often omit MGen, a negative chlamydia and gonorrhea result does not rule out MGen. If symptoms persist after treatment for another STI, asking specifically for an MGen test is important.

How to Prepare for an MGen Test

Preparation is simple but matters for accuracy. For a urine test, avoid urinating for about one to two hours before the sample and collect the first-catch urine, not midstream. For a swab, follow the collection instructions provided with your kit or at the clinic. Tell your clinician if you have taken antibiotics recently, since recent treatment can suppress the bacteria and cause a false negative. This guide is educational information, not medical advice.

Preventing MGen and Other STIs

MGen spreads through sexual contact, so consistent condom use reduces risk, and regular STI testing helps catch infections early, including those without symptoms. If you test positive, your sexual partners should be notified so they can be tested and treated too, which prevents reinfection. Many public health programs offer partner-notification tools that let you notify partners anonymously.