Most cats with this infection have already had a fecal test come back normal. That is not a mistake in the test — it is what the test is for. Here is which one to ask for, and how the sample should be taken.
A direct fecal smear — a drop of stool under a microscope — is quick, cheap, and finds this organism only around 14% of the time when the cat genuinely has it. There are three reasons, and they compound:
The usual way to tell them apart by eye is movement: this organism swims with a rapid, jerky, forward motion, while Giardia drifts like a falling leaf. That is a real skill, and it is not a reliable substitute for a DNA test.
Figures below are approximate and vary by study, assay and population — treat them as the shape of the problem, not as precise constants.
| Method | Sensitivity | Notes |
|---|---|---|
| Direct fecal smear | ≈14% | Must be fresh, never refrigerated. A negative tells you almost nothing. |
| Culture (InPouch TF) | ≈56–59% | Better, but slow, and still needs fresh handling. |
| PCR | ≈94% | The sensitive test. Detects DNA, so sample handling is less fragile. |
This is the detail most owner-facing material has not caught up with, and it matters.
Because the organism lives in the mucus on the colon wall, the historic advice was that washing the colon out — a colonic flush — gave the best sample. That advice was later described by the researchers themselves as having been based on anecdote.
Then it was measured. Across 1,717 cats, samples taken with a fecal loop — a small plastic loop used to scrape material from the rectal wall — were 2.04 times more likely to be PCR-positive than samples taken by colonic flush, and there was no significant difference between a flush and a plain voided stool.1 The authors suggested the loop works because it collects at the mucosal surface where the organisms actually adhere.
Because shedding is intermittent, the single best thing you can do is bring a sample taken while the cat is actively having diarrhea. If you can, take it in on the day rather than storing it.
Certain cat litters contain substances that inhibit the PCR reaction. A sample scraped from the cat rather than scooped from a tray avoids the problem entirely — another quiet argument for the loop.
Guidance from the European advisory body (ABCD) advises stopping oral antibacterials for around seven days before collecting a sample, on the reasoning that antibiotics reduce the organism or mask it.
But the same 1,717-cat study looked directly for that effect and found no association between prior antibiotic, antiparasitic, anticoccidial or corticosteroid treatment and a positive PCR result.1
So the guideline says withdraw and the largest dataset says it made no difference. Which one is right is not settled. This page presents both rather than picking the tidier version — and if your cat is currently on antibiotics for another reason, that is a question for your vet, not a reason to delay a test on this site's authority.
Stool appearance is genuinely useful, and it is also the most over-read thing in this whole condition. Here is the part that helps, then the part that misleads.
"Chronic diarrhea" is not one thing. The first fork is whether the problem sits in the small intestine or the large. This organism lives in the large intestine, so it produces the second column.
| Large bowel (colon) — the pattern here | Small bowel |
|---|---|
| Small volume, passed frequently | Large volume, passed less often |
| Mucus, often | Mucus unusual |
| Fresh red blood, often | Dark or digested blood, if any |
| Straining, urgency, tenesmus | Little straining |
| Weight loss late or mild | Weight loss often prominent |
| Markedly foul smell, frequently reported | Variable |
Veterinary practice uses standardized fecal scoring — most commonly a 1–7 scale, where 1 is hard and dry and 7 is watery with no form. It exists so that two people describing the same stool use the same words, and so that change over time can be measured rather than remembered.
Ask your veterinarian to record a fecal score at each visit, and note it yourself between visits. That single habit does more for monitoring than any photograph, because it is comparable and it is already used in your cat's record.
A fecal score describes the stool. It cannot tell you which organism is in it, so use the list below instead when you are deciding whether to book a visit — and take it with you.
North Carolina State University runs a dedicated Tritrichomonas diagnostic laboratory for this organism. Its stated policy is that it cannot advise cat owners directly and cannot return calls to owners, because of volume — but referring veterinarians can consult the senior researcher. Several commercial laboratories also offer the PCR.
