Fecal Samples – The Necessary Grossness

I’m going to be making a light post on Sunday because of the holiday, so instead of a news post today, I’ll be tackling a bigger topic.

Fecal floatations are the focus of today’s post. We always ask owners to bring a stool sample with them when their pet visits the hospital. This is an opportunity for us to check for intestinal worms and other parasites. “Worms” are a well-known concept to most owners. What’s lacking is the information about how we find the little buggers. You’ll be getting an up-close and personal look today.

I want to give some kudos where they’re due. Our veterinary technicians are the people that usually set up, run, and interpret our fecal samples. They handle poop all day long without complaint. It’s a nasty part of making sure our pets are healthy (and by extension their families, too). Thank you, Technicians!

We’re looking for evidence of worms and other parasites. Most of these nasty critters are attached to the intestinal wall in some fashion, so we don’t usually them in the pet’s stool. However, they shed eggs into the stool, and those eggs are what we’re searching for. In order to find them, we have to separate them from the fecal material. This whole process is designed to concentrate the eggs in one spot that we can sample. This gives us the best chance of finding them, and by extension, diagnosing the pet with adult intestinal worms.

Each photo is described/explained -after- the photo.

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This is part of the equipment needed to run a fecal sample. The blue pegboard thing is a test tube rack. The clear plastic tube is a test tube with a cone-shaped bottom. We use disposable dixie cups to avoid cross-contamination. The tongue depressor is used to move the stool sample from one step to the next.

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Samples need to be fresh. If they’re dried out, old, or frozen, the eggs can be hatched or damaged beyond our ability to find them. We know it’s gross to have you bring in poop, so here’s the kudos to owners for taking care of the collection part of the process. However, on that note, please notice that we don’t need a lot of stool. That’s a 50-cent-piece size, which is more than enough. We’ve had owners bring in the entire ziploc bag of stool, which is far more than we need. Just one little bit of formed stool is fine. If for the sake of not vomiting, by all means, grab the pile and run with it. 😉

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In this step, the stool is in the dixie cup. We’re adding a special liquid (Zinc Sulfate solution) to the cup.

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In this step, the stool is being broken up and mixed thoroughly with the Zinc Sulfate solution. We have to break up the stool to free the eggs from the fecal material. The end result is dissolved poop. It’s gross, yes.

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We then use a small funnel with a coarse filter in it to strain out the big chunks. We pour the liquid into the test tube.

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The test tube has to be filled right to the top of the tube, plus a tiny bit extra. We want to get a slight bulge of fluid on the top of the tube. As you can see, the cloudy brown liquid is the dissolved stool sample.

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A very thin square of glass called a cover slip is placed atop the fecal tube. The surface tension of the liquid is used to make the cover slip stick to the tube.

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The tube is placed in our centrifuge. A balance tube is put exactly opposite the fecal sample and filled with liquid to approximate the weight. We have to have the centrifuge balanced or it will self-destruct. Think about it as the same problem an unbalanced washer gets. (Whump-whump-whump-whump)

I have to explain a little bit of chemistry/physics here, so bear with me. The centrifuge spins the samples at a very high speed. (Again, just like the spin cycles on a washer.) We do this to get all of the big chunks to go to the bottom of the tube by way of gravity. The zinc sulfate solution in the tube is more dense than water (higher specific gravity). The eggs are lighter than most of the stool particles, so they will float up to the very top of the sample when the sample is spun. They concentrate right up against the cover slip. This is the critical step to getting a good result.

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As you can see in this sample, a lot of the stool particles have collected at the bottom of the tube. There are still some suspended in the liquid in this sample, but that’s a bit atypical for us to see. Usually the fluid is nearly clear.

We lift the cover slip off the top of the tube. The liquid right at the surface of the tube is pulled along with the cover slip, sticking to the bottom of it. The eggs are carried align with this small fluid sample. We place the cover slip down on a glass microscope slide.

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Here you can see the microscope slide (rectangular glass) with the cover slip stuck to it (square bit with the white edges/corners). The microscope has several different lenses that provide different levels of magnification. When we “read a fecal” we observe every single bit of the cover slip, looking for eggs.

I’ll show you the eggs we find below:

Hookworm
Hookworm

Roundworm
Roundworm

Whipworm
Whipworm

So, that’s what’s involved with “running a stool sample.” It’s a lot more involved than it seems. It’s a very important part of the twice-yearly checkups we recommend for pets. Hookworms and Roundworms are parasites that can be transmitted to human family members and other pets, so you definitely want to be sure your pet is checked twice a year.

It’s also a reminder that heartworm prevention ALSO prevents intestinal parasites. Keep your pets and you family protected with monthly prevention!

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9 Comments

Filed under laboratory, parasites, photos, preventive care, technician, zoonotic

9 responses to “Fecal Samples – The Necessary Grossness

  1. Chris Miner

    Fascinating! I do enjoy learning how tests are done. And it’s so important to check for parasites. And not so gross. There are way worse things 🙂

  2. Sue and John Foster

    Wow – I didn’t know half of that! Very helpful as always. Thanks!

  3. David

    Ooo, that’s fascinating stuff! Especially the centrifuging and mixing with solution and… stuff. Now I know what happens to those (ahem) samples we take along from Mischa. 🙂

    Here’s a question: what do you do with the excess that clients bring you? You know, if it’s a whole ziploc bag full, or even ‘just’ the average Great Dane-ful?

    I guess that question generalises to the question of how you dispose of biological waste in general…

  4. Valerie Lewis

    Very interesting. Please keep up the good work.
    Val

  5. Jessica

    What ml size is your test tubes?

  6. I believe they’re 12mL tubes. If you need more specific details, let me know. I can find out the manufacturer and part number for you. 🙂

  7. Jessica

    That would be great, if it’s not too much trouble.

  8. I’ll get you the info tomorrow when I’m back in the office. Thanks for reading the blog!

  9. Here’s the tube information:

    Jor-Vet
    Polystyrine
    15mL
    J0546A (part # ?)
    We buy in a box of 100 tubes.

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