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Liver shunt in dogs: bile acids, ammonia and the blood work clues

A portosystemic shunt is an abnormal blood vessel that lets blood from the intestine bypass the liver. Substances normally cleared by the liver, such as ammonia, then reach the brain. Most shunts are present from birth and are found in young dogs, often small breeds, sometimes from a routine blood test.

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

The essentials

A low urea (BUN), a low cholesterol and small red cells are classic clues on routine blood work. Bile acids before and after a meal are very sensitive: normal paired bile acids make a shunt unlikely, and high bile acids with a high ammonia make one very likely. Ammonium urate crystals or stones in the urine are common. CT angiography confirms the shunt and maps it before treatment. Most dogs with a single shunt outside the liver do well after surgery.

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Which dogs get a shunt

Shunts lie either outside the liver (extrahepatic) or inside it (intrahepatic); intrahepatic shunts are less common [1]. In 2,400 dogs, shunts were diagnosed in 0.18% of all dogs; the highest proportions were in the Havanese (3.2%), Yorkshire Terrier (2.9%), Maltese (1.6%), Dandie Dinmont Terrier (1.6%) and Pug (1.3%) [2]. Intrahepatic shunts run in families of Irish Wolfhounds [3].

Signs include neurological changes, digestive upsets and urinary problems; in dogs diagnosed at 5 years or older, neurological signs were the most frequent [4].

What routine blood work shows

  • Low urea (BUN): common, because the liver makes urea from ammonia [5].
  • Low cholesterol: a sign of reduced production by the liver [6].
  • Small red cells (microcytosis), often without anemia [7].

Bile acids and ammonia

Most dogs with a shunt have markedly high bile acids after a meal [8]. In 192 dogs, paired bile acids (before and 2 hours after a meal) detected every shunt, so normal paired bile acids make a shunt unlikely; fasting ammonia was less sensitive (77%) but more specific (93%) [9]. In another study, high fasting bile acids together with high ammonia had a specificity of 97% [10]. Puppies of predisposed breeds are best tested after 16 weeks of age [8].

An annotated line from a lab report · Illustrative example
AbbreviationResultUnitLaboratory intervalFlag
BA (2 h) Bile acids, post-prandial142µmol/L< 25H
  1. Abbreviation BA, SBA or bile acids; the 2-hour sample is taken after a meal.
  2. Result 142 µmol/L in this illustrative line: markedly high.
  3. Unit µmol/L.
  4. Laboratory interval An illustrative dog value; above 25–30 µmol/L suggests liver or blood-flow disease [8].
  5. Flag H: above the interval. In a young small-breed dog, a shunt is a leading cause. See the bile acids test.

Crystals and stones in the urine

Ammonium urate crystals look like brown “thorn-apples” under the microscope. Outside Dalmatians, English Bulldogs and Black Russian Terriers, they are rarely seen in normal dogs and are common with shunts [11]. In 363 dogs with a shunt, 19.3% had ammonium urate stones, 32.2% of those with a shunt outside the liver [12].

Imaging and outlook

Ultrasound finds many shunts, but CT angiography is the gold standard: in one study it detected 96% of shunts, against 68% for ultrasound [13, 14].

In 206 dogs with a single shunt outside the liver treated with an ameroid ring, 92% of the dogs followed long term had no signs, with an estimated median survival of 152 months [15]. Shunts inside the liver are more complex to treat [1].

Related articles

Bile acids test for dogs

How the fasting and 2-hour samples work.

Read the article

En français : le shunt porto-systémique du chien.

Questions to ask your veterinarian

  1. Are the urea, cholesterol and red cell size low?
  2. Should we measure bile acids before and after a meal, and ammonia?
  3. Does the urine show ammonium urate crystals or stones?
  4. Is a CT scan needed to locate the shunt?
  5. Is the shunt inside or outside the liver, and what are the options?
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Frequently asked questions

What is the life expectancy of a dog with a liver shunt?

After surgery for a single shunt outside the liver, most dogs do well: in one study the estimated median survival was 152 months [15].

Can a dog recover from a liver shunt?

Many dogs become free of signs once the shunt is closed; in one study, 92% of dogs followed long term had no signs [15].

Which breeds get liver shunts?

Havanese, Yorkshire Terriers, Maltese, Dandie Dinmont Terriers and Pugs had the highest proportions in a study of 2,400 dogs; Irish Wolfhounds have inherited shunts inside the liver [2, 3].

Why is urea low with a liver shunt?

Blood from the gut bypasses the liver, which normally turns ammonia into urea. Urea falls and ammonia can rise [5].

Do normal bile acids rule out a shunt?

Normal paired bile acids, before and after a meal, make a congenital shunt unlikely [9].

Sources

  1. Atiee GF, Cook AK. Intrahepatic congenital portosystemic shunts. Vet Clin North Am Small Anim Pract. 2025;55(4):699-716. doi.org/10.1016/j.cvsm.2025.03.002
  2. Tobias KM, Rohrbach BW. Association of breed with the diagnosis of congenital portosystemic shunts in dogs: 2,400 cases (1980-2002). J Am Vet Med Assoc. 2003;223(11):1636-1639. doi.org/10.2460/javma.2003.223.1636
  3. van Steenbeek FG et al. Evidence of inheritance of intrahepatic portosystemic shunts in Irish Wolfhounds. J Vet Intern Med. 2009;23(4):950-952. doi.org/10.1111/j.1939-1676.2009.0319.x
  4. Worley DR, Holt DE. Clinical outcome of congenital extrahepatic portosystemic shunt attenuation in dogs aged five years and older: 17 cases (1992-2005). J Am Vet Med Assoc. 2008;232(5):722-727. doi.org/10.2460/javma.232.5.722
  5. eClinPath, Cornell University College of Veterinary Medicine. Liver function tests. eclinpath.com/chemistry/liver/liver-function-tests
  6. eClinPath, Cornell University College of Veterinary Medicine. Cholesterol. eclinpath.com/chemistry/energy-metabolism/cholesterol
  7. eClinPath, Cornell University College of Veterinary Medicine. RBC indices interpretation. eclinpath.com/hematology/tests/rbc-indices-interpretation
  8. eClinPath, Cornell University College of Veterinary Medicine. Bile acids. eclinpath.com/chemistry/liver/liver-function-tests/bile-acids
  9. Devriendt N et al. Diagnostic value of liver function tests and ultrasonography in dogs with suspected congenital portosystemic shunts. Vet Rec. 2022;190(10):e1381. doi.org/10.1002/vetr.1381
  10. van Straten G et al. Diagnostic value of the rectal ammonia tolerance test, fasting plasma ammonia and fasting plasma bile acids for canine portosystemic shunting. Vet J. 2015;204(3):282-286. doi.org/10.1016/j.tvjl.2015.04.020
  11. eClinPath, Cornell University College of Veterinary Medicine. Urinalysis: crystals. eclinpath.com/urinalysis/crystals
  12. Walton-Clark M et al. Retrospective analysis of the incidence and clinicopathological findings associated with ammonium urate urolithiasis in dogs with congenital portosystemic shunts: 363 cases (2010-2023). J Small Anim Pract. 2025;66(4):248-257. doi.org/10.1111/jsap.13821
  13. Kim SE et al. Comparison of computed tomographic angiography and ultrasonography for the detection and characterization of portosystemic shunts in dogs. Vet Radiol Ultrasound. 2013;54(6):569-574. doi.org/10.1111/vru.12059
  14. Wilson S et al. Ferumoxytol-enhanced magnetic resonance angiography provides comparable vascular conspicuity to CT angiography in dogs with intrahepatic portosystemic shunts. Vet Radiol Ultrasound. 2021;62(4):463-470. doi.org/10.1111/vru.12963
  15. Falls EL et al. Long-term outcome after surgical ameroid ring constrictor placement for treatment of single extrahepatic portosystemic shunts in dogs. Vet Surg. 2013;42(8):951-957. doi.org/10.1111/j.1532-950X.2013.12072.x

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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