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Chronic diarrhea in dogs: tests, vitamin B12 and diet trials

Diarrhea that lasts for weeks, or keeps coming back, is one of the most common reasons dogs see the vet. The cause is usually found step by step: stool tests, blood work, special gut and pancreas tests, then diet trials. Here is what each test looks for and how to read the key results.

Written by the AI DiagAnimals editorial teamReviewed by the AI DiagAnimals TeamUpdated Our editorial policy

The essentials

Diarrhea is called chronic when it lasts 3 weeks or more. In most dogs the cause is in the gut itself, and the most common type improves with a change of diet. The work-up rules out parasites, pancreas problems and Addison’s disease first. Low albumin and low vitamin B12 point to more serious small-bowel disease and a less favorable outlook.

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What counts as chronic diarrhea

Vets call diarrhea chronic when it has lasted 3 weeks or more, whether it is constant or comes and goes [1, 3]. Many specialists now prefer the term “chronic enteropathy” (long-standing gut disease) to “inflammatory bowel disease”, because dogs respond very differently from people [14].

In a study of 136 dogs with chronic diarrhea, 90% had a disease of the gut itself. Gut inflammation was the cause in 71%, and two thirds of those dogs responded to a diet change. Infections, mostly parasites, accounted for 13% and tumors for 4%. The other 10% had a problem outside the gut: the pancreas in 6%, hormones in 2% [1].

Small bowel or large bowel signs

Your description of the stools helps the vet decide where the problem is, and which tests come first [1].

Some dogs have signs of both: studies call this diffuse disease [1].
Large bowel (colon)Small bowel
Typical signsFrequent small stools, mucus, fresh red blood, straining [4]Watery diarrhea, weight loss, low energy [1]
Blood workOften normal [4]More often low albumin and very low vitamin B12 [1]
In studiesYounger dogs with milder, mainly large bowel signs were more likely to respond to diet [1]Linked with a less favorable outcome [1]

What the stool and blood tests show

  • Fecal tests: a flotation and a Giardia antigen test are part of every work-up [1, 2]. Giardia was found in 11% of dogs in the 136-dog study [1]. See Giardia in dogs.
  • Blood count, chemistry and urinalysis: done in every dog, to rule out kidney, liver and other diseases that cause the same signs [2].
  • Albumin, globulin and cholesterol: low albumin, often with low globulin and low cholesterol, suggests the gut is leaking protein (protein-losing enteropathy). Low calcium and magnesium can go with it [2]. See albumin and globulin in dogs and protein-losing enteropathy.
  • Vitamin B12 (cobalamin) and folate: Low B12 points to disease of the small intestine [2]. It is low in 19–61% of dogs with chronic gut inflammation [2]. Folate is less useful: it is low in only 1–47% and is not specific [2, 8].
  • cTLI: checks that the pancreas makes digestive enzymes. A value under 2.5 µg/L with typical signs (big appetite, large volumes of stool, weight loss) confirms exocrine pancreatic insufficiency (EPI) [9]. The German Shepherd is one of the breeds most often affected [10].
  • Basal cortisol: screens for Addison’s disease. In 151 dogs with chronic gut signs, 4% had Addison’s, and none had the typical sodium or potassium changes [11]. A cortisol above 2 µg/dL (55 nmol/L) makes it very unlikely [12]. A low value is not a diagnosis: an ACTH stimulation test confirms or rules it out [2, 11].
  • Spec cPL (pancreatic lipase): a high value suggests the pancreas is also inflamed, and is linked with a less favorable outcome [2, 13]. See lipase and amylase.

Chronic gut inflammation is a diagnosis of exclusion: these tests are there to rule out the diseases that look like it [2]. More on Addison’s disease in dogs.

Reading a low vitamin B12 result

Low B12 is common: 36% of dogs with chronic gut disease had it in one study [6]. A normal value does not rule out gut disease [2].

An annotated line from a lab report · Illustrative example
AbbreviationResultUnitLaboratory intervalFlag
COB Cobalamin (vitamin B12)180ng/L244–959L
  1. Abbreviation COB, B12 or Cbl, depending on the laboratory.
  2. Result 180 ng/L in this illustrative line: clearly low.
  3. Unit ng/L, the same as pg/mL. Some laboratories report pmol/L.
  4. Laboratory interval 244–959 ng/L is the dog interval used in one study [7]. Each laboratory sets its own.
  5. Flag L: below the interval. Under 200 ng/L was a risk factor for a poor outcome in dogs with chronic enteropathy [5]. Very low B12 was also seen in 2 of 4 dogs with EPI in one study [1].

Diet trials, ultrasound and biopsies

  • Diet trial first: in a dog that is stable and eating, a strict diet trial is the preferred next step, before invasive tests. Between 38% and 89% of dogs with chronic gut inflammation respond to food [2].
  • How it works: the dog eats only a hydrolyzed or new-protein diet (or another therapeutic diet) for at least 2 weeks, with no treats or table food. Ideally, up to 3 different diets are tried before biopsies [2]. Most improvement on a hydrolyzed diet is seen within 2 weeks [2].
  • Abdominal ultrasound: looks at the gut wall, lymph nodes and other organs, mainly to rule out other diseases. It is advised especially with marked signs, weight loss of 5% or more, low albumin, or no response to diet [2].
  • Endoscopy and biopsies: a camera passed under general anesthesia takes small samples from the stomach, small intestine and colon [2]. Severe weight loss, a dog that will not eat, low albumin or thickened gut on ultrasound are reasons to do it sooner [3]. Biopsies cannot predict which dogs will respond to diet [2].

Outlook

Most dogs improve. In the 136-dog study, 87% reached full or partial remission. A poor outcome was linked with anemia (hematocrit under 40%), albumin under 2.0 g/dL and B12 under 200 ng/L [1]. In 70 dogs followed for 3 years, 18% were put to sleep because the disease could not be controlled; albumin under 20 g/L (2.0 g/dL) and low B12 were risk factors [5].

Dogs whose diarrhea responds to diet usually do very well long term [3]. After 12 to 14 weeks of remission, 31–79% stay well when the diet is changed again [2]. About 15–43% of dogs that need medication do not respond well enough [3], and dogs that lose protein through the gut have a poorer outlook [14].

Related articles

Other values often read together: cholesterol and triglycerides, hookworms.

For cats, see IBD in cats. En français : diarrhée chronique du chien.

Questions to ask your veterinarian

  1. Does this look like small bowel or large bowel diarrhea?
  2. Have the stool tests, including Giardia, been done?
  3. Are albumin, vitamin B12, cTLI and cortisol in range?
  4. Which diet should we try, for how long, and what counts as a response?
  5. At what point would you recommend ultrasound or biopsies?
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Frequently asked questions

Why does my dog keep getting diarrhea every few weeks?

Diarrhea that comes and goes is typical of chronic gut disease [1, 4]. The most common cause in studies is gut inflammation that improves with a change of diet; parasites such as Giardia, pancreas problems and Addison’s disease are other causes [1, 11]. Once it has lasted 3 weeks, a work-up is worthwhile [1].

What is a red flag for diarrhea in a dog?

Weight loss, a poor appetite and low albumin are reasons to investigate sooner [3]. Swelling or fluid in the belly suggests protein loss [2]. Black or bloody stools were seen in 4 of 6 dogs whose chronic signs turned out to be Addison’s disease [11].

How do you treat chronic diarrhea in dogs?

It depends on the cause, so the tests come first. Parasites, EPI and Addison’s disease each have their own treatment. For gut inflammation, a strict diet trial is usually the first step in a stable dog, and many dogs respond to diet alone [2]. Your vet decides on medication if diet is not enough.

How long does a diet trial take?

At least 2 weeks of feeding only the new diet. If it does not work, other diets are tried, ideally up to 3, before biopsies [2]. Dogs with intermittent signs may need longer to judge [2].

Can a blood test find the cause of chronic diarrhea?

It helps but rarely gives the answer alone. Blood tests rule out other diseases and show clues such as low albumin, low B12, a low cTLI (EPI) or a low cortisol (Addison’s) [2, 9, 11].

Sources

  1. Volkmann M et al. Chronic Diarrhea in Dogs – Retrospective Study in 136 Cases. J Vet Intern Med. 2017;31(4):1043-1055. doi.org/10.1111/jvim.14739
  2. Heilmann RM et al. ACVIM-endorsed statement: consensus statement and systematic review on guidelines for the diagnosis and treatment of chronic inflammatory enteropathy in dogs. J Vet Intern Med. 2026;40(1):aalaf017. doi.org/10.1093/jvimsj/aalaf017
  3. Jergens AE, Heilmann RM. Canine chronic enteropathy – current state-of-the-art and emerging concepts. Front Vet Sci. 2022;9:923013. doi.org/10.3389/fvets.2022.923013
  4. Leib MS. Treatment of chronic idiopathic large-bowel diarrhea in dogs with a highly digestible diet and soluble fiber: a retrospective review of 37 cases. J Vet Intern Med. 2000;14(1):27-32. pubmed.ncbi.nlm.nih.gov/10668813
  5. Allenspach K et al. Chronic enteropathies in dogs: evaluation of risk factors for negative outcome. J Vet Intern Med. 2007;21(4):700-708. pubmed.ncbi.nlm.nih.gov/17708389
  6. Berghoff N et al. Serum cobalamin and methylmalonic acid concentrations in dogs with chronic gastrointestinal disease. Am J Vet Res. 2013;74(1):84-89. doi.org/10.2460/ajvr.74.1.84
  7. Toresson L et al. Comparison of efficacy of oral and parenteral cobalamin supplementation in normalising low cobalamin concentrations in dogs: a randomised controlled study. Vet J. 2018;232:27-32. doi.org/10.1016/j.tvjl.2017.12.010
  8. Ullal TV et al. Association of folate concentrations with clinical signs and laboratory markers of chronic enteropathy in dogs. J Vet Intern Med. 2023;37(2):455-464. doi.org/10.1111/jvim.16681
  9. Wiberg ME et al. Serum trypsinlike immunoreactivity measurement for the diagnosis of subclinical exocrine pancreatic insufficiency. J Vet Intern Med. 1999;13(5):426-432. pubmed.ncbi.nlm.nih.gov/10499725
  10. Batchelor DJ et al. Breed associations for canine exocrine pancreatic insufficiency. J Vet Intern Med. 2007;21(2):207-214. pubmed.ncbi.nlm.nih.gov/17427378
  11. Hauck C et al. Prevalence and characterization of hypoadrenocorticism in dogs with signs of chronic gastrointestinal disease: a multicenter study. J Vet Intern Med. 2020;34(4):1399-1405. doi.org/10.1111/jvim.15752
  12. Gold AJ et al. Evaluation of basal serum or plasma cortisol concentrations for the diagnosis of hypoadrenocorticism in dogs. J Vet Intern Med. 2016;30(6):1798-1805. doi.org/10.1111/jvim.14589
  13. Kathrani A et al. Elevated canine pancreatic lipase immunoreactivity concentration in dogs with inflammatory bowel disease is associated with a negative outcome. J Small Anim Pract. 2009;50(3):126-132. doi.org/10.1111/j.1748-5827.2008.00693.x
  14. Dandrieux JR. Inflammatory bowel disease versus chronic enteropathy in dogs: are they one and the same? J Small Anim Pract. 2016;57(11):589-599. doi.org/10.1111/jsap.12588

Laboratory methods and reference intervals vary. This article explains; it does not diagnose. For a decision about your pet, use the original report and talk to your veterinarian. Our editorial policy.

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