Collecting a stool sample is straightforward once you know the setup. The basic process involves catching stool in a clean container before it touches toilet water, transferring the right amount into the collection kit your doctor or lab provided, and getting it to the lab within the required window. Most people can do the whole thing in under five minutes.
What to Avoid Before Collection
Certain substances can contaminate your sample and force you to redo the test. Before collecting, stop using antacids, bismuth products (like Pepto-Bismol), anti-diarrheal medications (like Imodium), and oily laxatives including castor oil and mineral oil. Fiber supplements like Metamucil can also interfere. Your lab instructions should specify how long to avoid these, but a general rule is at least 48 hours beforehand.
If you’ve recently had a barium enema for imaging, wait 7 to 10 days before collecting a specimen. Barium residue makes the sample unusable. The same goes for barium swallow tests.
One notable exception: if you’re doing a fecal immunochemical test (FIT) for colorectal cancer screening, you don’t need to change your diet at all before testing. The older guaiac-based fecal occult blood test (FOBT) sometimes required avoiding red meat and certain vegetables, but FIT has no dietary restrictions.
How to Catch the Sample
The most important rule is that your stool cannot touch toilet water, urine, or toilet paper. Any of these will contaminate it. Here’s how to set up a clean catch:
- Plastic wrap method: Drape a sheet of plastic wrap loosely across the toilet bowl, pressing it down slightly in the center to create a shallow cradle. The wrap sits just above the water line. After you have a bowel movement onto the wrap, you can easily scoop from it.
- Collection hat: Some labs provide a shallow plastic basin (sometimes called a “hat”) that sits under the toilet seat rim. This catches everything and keeps it separate from the bowl water.
- Clean dry container: If you don’t have a hat or plastic wrap, any clean, dry container that you can position under you will work. A disposable aluminum pan or a clean plastic container you plan to throw away are both fine.
If you’re collecting from a child in diapers, you can scoop the sample directly from the diaper as long as urine hasn’t soaked into the same area.
If You Have Diarrhea
Liquid stool is harder to catch with plastic wrap because it tends to slide off. A more reliable method is taping a plastic bag to the underside of the toilet seat so it hangs into the bowl like a liner. After collection, you can carefully pour or scoop from the bag into your specimen container. Liquid stool is perfectly acceptable for most tests.
Transferring the Sample
Most collection kits come with a small spoon or spatula built into the container lid. Use this to scoop stool from your catching surface into the specimen container. Fill the container roughly halfway, or about the size of a walnut if your kit doesn’t specify an exact amount. Don’t overfill it, especially if the container holds a liquid preservative, since the stool needs room to mix with the solution.
If your kit contains a preservative vial, the general ratio is one part stool to three parts preservative. Some kits have a fill line marked on the side. Screw the lid on tightly and gently shake or swirl the container to mix the stool with the preservative.
For FIT kits (colorectal screening), the process is slightly different. You’ll typically use a small probe or brush to collect a tiny smear from the surface of your stool, then insert it back into the sealed tube. You only need a very small amount. FOBT cards, by contrast, require you to smear small samples from three consecutive bowel movements onto the card’s test windows, two smears per movement.
Label the container with your name, date of birth, and the date and time of collection. Most labs provide a label or form for this. Getting the time right matters because it tells the lab how fresh the sample is.
Storage and Timing
How quickly you need to deliver the sample depends entirely on what test is being run, and the differences are significant.
Stool cultures and parasite exams are the most time-sensitive. Unpreserved stool for culture needs to be placed in its container within two hours of the bowel movement and ideally refrigerated right away. The same two-hour window applies to ova and parasite (O&P) exams and gastrointestinal infection panels, though once the stool is in a preservative vial, O&P samples stay stable for up to two weeks at room temperature.
Other tests are more forgiving. Occult blood samples on hemoccult cards remain stable at room temperature for up to 14 days. Calprotectin samples (used to measure gut inflammation) last four days at room temperature and 10 days refrigerated. H. pylori antigen tests are good for 72 hours in the fridge.
When in doubt, refrigerate the sample immediately after collection and deliver it to the lab as soon as possible, ideally the same day. Place the sealed container inside a zip-lock bag to prevent leaks, and keep it in a part of the refrigerator away from food. Do not freeze a sample unless your lab specifically tells you to.
Practical Tips That Make It Easier
Try to collect your sample in the morning if you need to drop it off at a lab that day. Most labs have morning hours, and this gives you the widest window before any freshness deadline.
Urinate first, before setting up your collection surface. This reduces the chance of accidentally contaminating the stool with urine, which is one of the most common reasons labs reject samples. If you can’t fully empty your bladder beforehand, the plastic wrap or hat method helps keep the two separate since urine tends to run off while stool stays on the surface.
Wash your hands thoroughly with soap and water both before and after collection. Wear disposable gloves if you have them. Dispose of the plastic wrap, bag, or hat in a tied-off trash bag. Clean any surfaces that may have been contacted.
If your collection kit came with multiple vials or containers, fill all of them from the same bowel movement unless the instructions specifically say to use separate movements. Some parasite tests do require samples from different days, typically three specimens collected on alternate days, to increase the chance of detection.
Transport the sample in a cooler with an ice pack if you have a drive longer than 30 minutes to the lab, especially in warm weather. Keep the container upright to prevent leaks. Most labs will accept walk-in specimen drop-offs without an appointment, but calling ahead to confirm hours can save you a trip.