Gliotoxin Test

If you have been living or working in a water-damaged building, or if you have unexplained fatigue, respiratory symptoms, or immune problems that standard bloodwork cannot explain, this test looks for a specific toxin that certain molds produce. Finding it in your urine means your body has recently absorbed it, most likely through inhaling contaminated air or ingesting contaminated food.

Gliotoxin is not something your body makes. It is a poison produced by molds, primarily Aspergillus fumigatus, one of the most common airborne fungi in indoor and outdoor environments. Because it powerfully suppresses multiple branches of the immune system (based on laboratory and animal research), even low-level chronic exposure is a concern worth investigating.

What Gliotoxin Is and Where It Comes From

Gliotoxin belongs to a family of sulfur-rich fungal poisons called epipolythiodioxopiperazines (ETPs). It was first described in the 1930s, and its chemical structure was confirmed by X-ray imaging in 1966. The molecule's defining feature is a reactive sulfur bridge that allows it to latch onto proteins inside your cells and generate unstable oxygen molecules that damage tissue.

The primary producer is Aspergillus fumigatus, a mold that thrives in damp building materials, compost, and soil. Other fungi, including certain Trichoderma and Penicillium species, can also produce it or closely related toxins. The mold releases gliotoxin as a secondary metabolite, essentially a chemical weapon it uses to suppress the immune defenses of whatever host it invades.

How It Affects Your Immune System

Based on decades of laboratory and animal research, gliotoxin is one of the most potent natural immune suppressors identified. It targets nearly every major branch of immune defense. It blocks macrophages (the large immune cells that engulf invaders) from attaching to and swallowing pathogens. It suppresses the multiplication of lymphocytes, the white blood cells responsible for targeted immune responses. It interferes with neutrophils, the first responders that rush to sites of infection.

It also disrupts dendritic cells, which are responsible for presenting fragments of invaders to T cells so they can mount a specific defense. And it can trigger programmed cell death in mast cells and eosinophils, immune cells involved in allergic and parasitic responses. This breadth of immune suppression is what makes gliotoxin a key factor in how Aspergillus establishes and maintains infections in vulnerable people.

What a Positive Urine Result Means

This test measures gliotoxin in your urine. A detectable level indicates that your body has been exposed to, absorbed, and is now excreting this mycotoxin. The most common routes of exposure are breathing contaminated indoor air and eating contaminated food. The presence of gliotoxin in urine does not by itself diagnose a specific disease, but it confirms meaningful mold exposure and raises the question of whether that exposure is affecting your health.

In clinical research, a more stable breakdown product called bis(methylthio)gliotoxin (bmGT) has been studied as a potential marker of invasive Aspergillus infection. However, studies in patients with blood cancers and confirmed invasive aspergillosis found that bmGT was detectable in serum in only 1 out of 18 patients with proven disease, and one prospective study found it negative in all 15 confirmed cases tested. This means that blood-based gliotoxin and bmGT testing has poor sensitivity for diagnosing active Aspergillus infection. The urine test you are taking serves a different purpose: it detects environmental mycotoxin exposure rather than diagnosing acute fungal infection.

Who Is Most Vulnerable

People with weakened immune systems face the greatest risk from gliotoxin exposure. This includes anyone on immunosuppressive medications (such as corticosteroids or chemotherapy), organ transplant recipients, and people with HIV or other conditions that reduce immune function. In these populations, Aspergillus fumigatus can cause invasive aspergillosis, a life-threatening lung or systemic infection where gliotoxin acts as a major weapon the fungus uses against your defenses.

But you do not need to be severely immunocompromised to be affected. People living or working in water-damaged buildings with chronic mold exposure may absorb low levels of gliotoxin over months or years. Given its broad immune-suppressive effects (demonstrated primarily in lab and animal studies), even ongoing low-level exposure could theoretically make you more susceptible to infections or slower to recover from illness, though long-term outcome studies in this population have not been conducted.

Reference Ranges

No major clinical guidelines or consensus bodies have established standardized reference ranges for urinary gliotoxin. This is a research-grade and specialty lab marker. The lab performing your test will report its own analytical detection limits and flag whether your result is above or below the reportable threshold. Because assay methods and detection limits vary between laboratories, you should interpret your result relative to the specific lab's reference values rather than comparing it to published numbers from a different lab or method.

In general, the goal is for gliotoxin to be undetectable or below the lab's reporting threshold. Any detectable level warrants attention, because this is not a molecule your body produces. Its presence confirms external exposure.

When Results Can Be Misleading

A negative result does not guarantee zero mold exposure. Gliotoxin is chemically unstable and breaks down relatively quickly. If your exposure occurred days or weeks before the test, levels may have already fallen below the detection threshold. Timing matters: a urine sample collected during active, ongoing exposure is more likely to be informative than one collected after you have already left a contaminated environment.

Hydration status can also affect urine concentration. A very dilute sample (from drinking large amounts of water before collection) might push a borderline level below the detection limit. Conversely, a highly concentrated sample could amplify a trace amount. Some labs normalize results to urine creatinine to correct for this, but not all do.

How This Differs from Other Aspergillus Tests

If your doctor suspects an active Aspergillus infection, the standard diagnostic markers are galactomannan (GM, a sugar fragment shed from the fungal cell wall) and beta-D-glucan (BDG, another component of fungal cell walls), both measured in blood. Multiple meta-analyses have confirmed that these markers have far better sensitivity and specificity for diagnosing invasive aspergillosis than gliotoxin or its derivative bmGT. A meta-analysis of serum GM and BDG testing found that combining the two improves diagnostic sensitivity for invasive aspergillosis.

Urinary gliotoxin testing is not a replacement for GM or BDG when active fungal infection is suspected. Its value lies in a different question: has your body been absorbing mold toxins from your environment? That is an exposure question, not an infection question, and the two serve different clinical purposes.

Tracking Your Trend

A single gliotoxin measurement is a snapshot. Because the molecule breaks down quickly and urine concentrations can vary with hydration, timing, and ongoing exposure levels, one reading may not capture the full picture. If your initial test is positive, retesting after you have taken steps to reduce exposure (such as mold remediation in your home or workplace) can show whether those efforts are working.

A reasonable approach is to test at baseline when you suspect mold exposure, retest 2 to 3 months after remediation or after leaving the contaminated environment, and then check again at 6 months to confirm the level has stayed down. If you are in an environment where ongoing exposure is unavoidable (certain occupations, for example), testing every 6 to 12 months gives you a longitudinal picture of your body's mycotoxin burden.

What to Do with an Abnormal Result

If gliotoxin is detected in your urine, the first step is to identify and address the source of exposure. A professional mold inspection of your home and workplace is the most direct next action. Environmental testing can identify whether Aspergillus species are present and at what levels.

On the medical side, consider ordering the full mycotoxin panel if you have not already, since mold-contaminated environments typically harbor multiple toxin-producing species. Companion blood tests that help evaluate whether your immune system is under stress include a complete blood count with differential (to check white blood cell populations), immunoglobulin levels (IgA, IgG, IgE), and inflammatory markers like hs-CRP (high-sensitivity C-reactive protein, a measure of body-wide inflammation). If you have respiratory symptoms, an allergist or pulmonologist can evaluate for allergic bronchopulmonary aspergillosis or chronic pulmonary aspergillosis using imaging and additional testing.

Because this is a Tier 3 marker without standardized clinical decision thresholds, a positive result should be interpreted alongside your symptoms, environmental history, and other lab findings rather than acted on in isolation. The pattern of evidence matters more than any single number.