Congenital portosystemic shunts (PSS) are usually diagnosed in young dogs (under 2 years of age) as a result of a combination of nonspecific symptoms. The results of a urinalysis and routine blood work (a complete blood count and a serum biochemistry profile) are typically unremarkable in dogs with portosystemic shunts, although there may be an elevation in liver enzymes, and some changes in blood urea nitrogen (BUN) levels. Abdominal radiographs (X-rays of the belly) may reveal a small liver (microhepatica) and/or abnormalities in the kidneys. More definitive diagnosis is made by drawing blood samples and submitting them to a diagnostic laboratory for preprandial (fasted) and postprandial (after a meal) serum bile acid tests.
Abdominal ultrasound done by a skilled ultrasonographer may actually identify a PSS and/or an abnormally small liver. Other advanced diagnostic imaging techniques include portovenography, transcolonic or colorecytal portal scintigraphy and radiographic mesenteric portography. Mesenteric portography is considered to be the gold standard for diagnosing a PSS. A liver biopsy is recommended in almost all cases of suspected portosystemic shunts, to assess the nature and extent of liver damage. A fine needle aspirate can also be taken, but while it is a less invasive procedure than a biopsy it does not provide as good a sample for diagnostic purposes. Radiographic studies using contrast media are also available to diagnose a PSS. Many of these tests are only available at specialized referral centers and at veterinary teaching hospitals.
Puppies of high-risk breeds can be screened for portosystemic shunts by measuring the concentration of bile acids and/or ammonia in their blood. Unfortunately, these tests can have false positive results, and no puppy should be labeled as having a PSS - and certainly should not be euthenized - based solely on the results of a blood test. The best way to diagnose a PSS is through abdominal ultrasound. This technique is highly specific and very sensitive for the diagnosis of a portosystemic shunt.