Clostridium Hathewayi

This stool marker counts DNA from one particular gut bacterium. A positive result is not an infection diagnosis. The reason anyone measures it is colorectal cancer: stool levels run higher in people with colorectal cancer than in healthy controls, while its usefulness for finding precancerous polyps is much weaker.

The catch is that it does not do enough alone. On its own it can separate colorectal cancer from healthy controls only modestly, and it cannot reliably tell a precancerous polyp apart from healthy stool. Its value comes from being read alongside a few other bacterial markers and, ideally, a stool blood test.

What the Test Actually Counts

Clostridium hathewayi is a living organism, not a protein or hormone your body makes. It is an anaerobe. That means it grows where there is little oxygen, which describes much of your colon. It was reclassified in 2014 and now goes by Hungatella hathewayi, so older papers and newer ones are often talking about the same organism under two names.

The assay extracts DNA from your stool sample and uses PCR to measure how much of this organism's genome is present. PCR copies a specific stretch of DNA many times so it can be counted. So the number reflects bacterial DNA in stool, not anything your own cells produced. Targeted PCR counts of this marker track closely with sequencing of the whole stool sample.

It is a normal resident, not an invader. It was first described from human stool, and a survey of healthy community volunteers in England found it in a meaningful share of them. Detecting it can be normal. The question is how much, and what else is happening around it.

Colorectal Cancer

The strongest evidence is in colorectal cancer. Studies that compare stool samples at one point in time, plus larger stool-DNA sequencing studies pooling many cohorts, find this organism enriched in people with colorectal cancer compared with healthy controls, with the largest increases in late-stage disease. The pattern also appears in both young-onset and older-onset disease.

But read on its own, it is a mediocre test. In a prospective multicenter cohort, it reached an area under the curve of 0.63 for colorectal cancer and 0.59 for advanced adenoma. An area under the curve is a score from 0.5 to 1.0 for how well a test separates people with a condition from people without it. A score of 0.5 is a coin flip. These numbers are close to that.

Panels change the picture. A model combining this marker, the m3 Lachnoclostridium marker, Fusobacterium nucleatum, Bacteroides clarus, and a fecal immunochemical test reached 93.8% sensitivity and 81.2% specificity for colorectal cancer. That means it caught about 94 of every 100 cancers while correctly clearing about 81 of every 100 people without cancer. In asymptomatic people, a four-bacteria panel caught 84.9% of colorectal cancers compared with 66.7% for the stool blood test alone.

The signal is not consistent in every population. In a 2026 population-based screening study in Norway, among people who had already tested positive on a stool blood test, this organism was more abundant in those whose colonoscopy found nothing than in those who turned out to have a tumor or polyp. Among people who bleed for some other reason, its presence may say nothing about cancer risk at all. That is a large slice of the people most likely to be running this marker.

A high result here is a reason to make sure your colonoscopy is current, not a reason to conclude you have cancer. Colonoscopy remains the test that finds and removes polyps. This marker, at best, helps decide how urgently to schedule it.

Precancerous Polyps, and Why This Marker Misses Them

This is the limitation that matters most for prevention. This organism discriminates colorectal cancer from healthy controls, but on its own it cannot reliably separate adenomas, the precancerous polyps that many cancers grow out of, from healthy controls. If you are testing to catch something early, that is the exact window you care about.

This is why panels pair it with other markers. On its own this marker reached an area under the curve of only 0.620 for telling adenoma apart from healthy controls. A Lachnoclostridium marker called m3 covers more of that gap at 0.675, and Fusobacterium nucleatum carries more of the cancer signal, at 0.862 on its own. Bacteroides clarus runs the other direction, enriched in healthy people, which gives the panel a baseline to score against.

Watching for Polyp Recurrence After a Colonoscopy

The least speculative use of this marker is not a one-time screen. It is tracking change in someone who has already had polyps removed. Even there, it is still research-grade surveillance, not a replacement for scheduled colonoscopy.

In a polyp-surveillance study with paired baseline and follow-up stool samples, measuring this organism alongside the m3 marker and Fusobacterium nucleatum at both time points identified recurrent adenomas with 90.0% sensitivity and 87.0% specificity. The area under the curve was 0.95. The standard stool blood test caught 8.3% of the same recurrences.

Be careful about how much of that came from this marker. In people whose polyps did not come back, levels of this organism drifted down over time, but the change did not reach statistical significance on its own. The significant movement came from the other two markers. This one contributed as part of a three-marker pattern rather than as a signal you could read by itself.

If you have had polyps removed, a same-lab baseline after the procedure and a repeat near surveillance colonoscopy can make the result more interpretable. A panel that is holding steady or rising when it should be falling is a reason to prioritize colonoscopy, not to treat the stool number.

Inflammation and Illness Severity

Levels can rise in settings that have nothing to do with colorectal cancer. In a small stool study of hospitalized COVID-19 patients who had not received antibiotics, baseline fecal abundance of this organism correlated with disease severity, though that part of the analysis rested on only seven patients. A large multiple sclerosis study also found higher proportions of this organism in people with MS, with stronger signals in progressive disease.

Those were sequencing studies of stool, not this targeted stool PCR readout, so they matter mainly as confounders. None of this proves the bacterium causes those illnesses. The pattern that fits best is that this organism can expand when the gut community is disrupted. In those settings it looks more like a passenger than a driver.

The Longevity Finding, and How to Square It

If higher were simply worse, this next result would not exist. In studies of long-lived populations, this same organism was enriched in the gut, showing up as one of a handful of longevity-associated species. Genomic modeling of those samples pointed toward purine breakdown, a housekeeping metabolic job, rather than anything harmful.

The way to hold both findings at once: this is not a good-number, bad-number marker. It is a commensal that expands under certain gut conditions, and the meaning of that expansion depends on the context you measure it in. Enriched in a stool panel built to detect colorectal tumors, it is a risk signal. Enriched in a healthy 100-year-old, it may just be part of an old, established gut community. The bacterium is the same. The question being asked is different.

Mendelian randomization uses inherited genetic differences as a natural experiment. In the longevity study, that analysis suggested the broader Hungatella group may be linked with parental longevity, but it did not prove that this exact species makes people live longer. That is a weaker claim than the stool enrichment.

On the cancer side, human evidence still places this organism as an opportunistic passenger rather than a proven cause of tumors. Laboratory work has started to complicate that. In cell experiments, a compound this bacterium releases pushes colon cells toward the migrating, invasive behavior that tumors use to spread, and earlier work found it could help switch off genes that normally hold tumor growth in check. None of that has been shown to happen in people. For now it is a flag with a plausible mechanism behind it, not a demonstrated culprit.

Why One Reading Is Thin

The gut microbiome moves. In daily quantitative profiling of healthy adults, 78% of gut microbial genera varied more within the same person over time than between different people, with stool moisture and diet as major drivers. That figure depends on the method: using conventional relative-abundance data instead, it was 36%. Either way, a single stool sample is a snapshot of a community that may look different next week.

Lab method adds more noise. DNA extraction method alone can shift measured gut microbiome diversity, which is why the same sample can give different answers at different labs. Over longer windows the picture is steadier: in a two-year study, the overall fecal microbiome was relatively stable, though individual taxa still moved around.

So the design that works, if you use it, is serial and same-lab. Get a baseline tied to the reason you are testing. Repeat with the same lab if you are tracking a change. Compare your level to your own previous level, not to a published cutoff, because standardized clinical cutpoints for this organism do not exist.

When a Reading Can Fool You

Several things can distort a single result without changing anything about your colorectal cancer risk.

• Day-to-day swings: most gut genera vary substantially over time, driven partly by stool consistency and diet, so a level that jumps between two samples a week apart may reflect what you ate or how fast stool moved through.
• Lab method differences: DNA extraction and sequencing choices measurably change the numbers. Switching labs mid-track makes your trend hard to read.
• Acute illness: levels can rise during serious illness such as severe COVID-19. Testing during or shortly after a hospitalization gives you a number about that illness, not just your colon.
• Recent antibiotics: the studies that built these panels often excluded people with antibiotic exposure in the prior 3 months. Antibiotics reshape the gut community, so a sample taken soon after a course may not represent your usual state.
• A positive stool blood test already in hand: in a population-based screening study, this organism was more abundant in people whose follow-up colonoscopy was clear than in those with a real lesion, so it may add little once you already know you are bleeding.

What to Do With an Out-of-Pattern Result

An unexpectedly high level, or a level that climbs when recurrence studies suggest it should fall, should change what you check next. It should not start antibiotics.

Order the rest of the panel rather than this marker alone. The m3 Lachnoclostridium marker covers more of the adenoma window this one misses, Fusobacterium nucleatum strengthens the cancer signal, and Bacteroides clarus provides the healthy-gut baseline. Pair the panel with a fecal immunochemical test. That test detects hidden blood in stool, a different biological signal. Adding the stool blood test to a four-marker microbial panel pushed sensitivity to 93.8% in one study.

Then look at the combination. A high bacterial score with a positive stool blood test is a strong reason to book colonoscopy promptly. A high bacterial score with a negative stool blood test in someone due for screening still favors booking rather than waiting. An isolated high level in someone with a clean recent colonoscopy and no symptoms is better handled as a trend question: repeat at the same lab and watch the direction.

Bring a gastroenterologist in if you have had polyps removed and your panel is not falling, if there is a family history of colorectal cancer, or if you have any red-flag symptoms such as rectal bleeding, a persistent change in bowel habit, or unexplained weight loss. Those symptoms go straight to colonoscopy regardless of what any stool marker says. The panel work has not been validated in people with hereditary colorectal cancer syndromes, active bowel inflammation, or recent antibiotic exposure, because those groups were excluded from key studies. If you are in one of them, the marker has no established meaning for you and standard screening is what counts.