Diarrhoea in Dogs and Cats: Stool Tests Beyond the Basics

When a dog or cat has diarrhoea, a routine stool test is usually the first step. If the cause is still unclear, a vet may add a test for hidden blood, a smear for moving protozoa, a Giardia kit or a stool culture. Each one answers a different question about the gut.

What does the routine stool test already tell you?

A Stool Routine test notes the colour, smell and consistency of the stool, then looks for mucus, blood and undigested food. A small amount is also viewed under the microscope for worm eggs, cysts and other parasites. For many pets this one test gives the vet enough direction. It cannot catch everything, though. Some parasites are passed only now and then, and bacteria need a different kind of test, which is why the tests below exist.

Do not wait for results if your pet is a puppy or kitten, is old, is vomiting as well, seems weak or has blood in the stool. These pets can lose fluid fast and need a vet promptly.

When does a vet look for hidden blood?

Blood that comes from higher up in the gut is partly digested on the way out, so it may not look red. It can turn the stool very dark, or it may not be visible at all. The Stool Occult Blood test finds tiny amounts of blood that the eye cannot see, and it can help show bleeding somewhere in the digestive tract. It does not say where or why. Some foods can mislead this test, so your vet may ask you to change what your pet eats for a while before the sample is taken.

How do the two Giardia checks differ?

Giardia is a tiny single-celled parasite that lives in the gut. The Faecal Direct Smear (Protozoa) test looks at a drop of very fresh stool under a microscope for protozoa that are still moving. They stop moving and break down soon after leaving the body, so call the lab before you collect a sample for this test.

The Giardia Faecal Antigen (Rapid Test) is a kit that detects antigen, a protein from the parasite, in fresh stool. Giardia is passed on and off, so a negative result does not always rule it out. Your vet may ask for samples from more than one day, or may use the kit together with the smear.

When is a stool culture added?

A Stool Culture & Sensitivity test grows bacteria from the stool on special plates. It can find disease-causing germs such as Salmonella, and the sensitivity part shows which antibiotics the bacteria respond to, which helps your vet plan treatment. It is more often used when diarrhoea is severe, keeps returning or contains blood. A healthy gut also holds plenty of harmless bacteria, so growth on the plate has to be read together with your pet's signs. Tell the lab if your pet has already had antibiotics.

Salmonella and some other gut germs can pass to people. Wash your hands well after handling stool, wear gloves to collect it, and speak to a doctor if anyone at home has diarrhoea.

How should you collect the sample?

• Use a clean container with a lid, and a fresh one for each sample.
• Pick the stool up from a clean surface such as paper or a plastic sheet, not from soil or grass.
• A spoonful or so is enough.
• For a cat, take stool from the tray soon after it is passed and pick out any litter granules.
• Write your pet's name and the time on the label.
• Keep the container closed and cool, and bring it quickly.

Make a note of your pet's food, medicines, deworming and any recent change at home. A registered veterinarian reads the stool results with that history, so these details matter as much as the sample.

Read next

For the youngest patients, Kitten Diarrhoea and the Stool Tests a Vet May Ask For explains what tests suit a kitten with loose motions. If you are checking a young dog for worms, Worm Checks in Puppies: Stool Tests Explained covers the stool tests used for that.

Testing in Bhopal

Because a fresh stool sample matters so much, tell the lab at C-200, C Sector, Shahpura, Bhopal what your pet is passing before you collect anything. Pick-up is free anywhere in Bhopal. Outside the city, samples can come by courier, bus parcel or through your vet, and the lab will tell you which tests need a very fresh sample. Call or WhatsApp +91 88175 01118; the lab confirms the method, sample needs and reporting time when you book.