Introduction: The liver plays a key role in most of the body functions of all animals, including dogs. So it follows that problems in organs other than the liver are often reflected in changes in liver function. And of course, a problem in the liver itself can be the primary cause of liver malfunction. The liver is a very resilient organ with lots of reserve, a double-edged sword when considering how to diagnose and treat liver disease in dogs – it can function at a seemingly normal level even if 70-80 percent of the organ is compromised. Because of this, a chronic liver problem may exist for a long time before symptoms appear that the dog owner, or even the veterinarian, will recognize. When symptoms finally do appear, they can be many and varied, including but not limited to loss of appetite, vomiting or diarrhea, lethargy, an enlarged abdomen, weight loss, color changes in feces or urine, or even seizures. Many vets recommend a yearly check of a blood sample for “liver values” and other factors, to identify these often hidden liver malfunctions as early as possible. Here is a simplified description of these measurements and what they may indicate, followed by a description of some of the more common liver problems in dogs.
Parameter Normal range
ALT 10-84 U/L
AST 5-55 U/L
ALKP 2-200 U/L
Tot BILI
Albumin 2.5-4.3 g/dL
BUN 9-27 mg/dL
“Liver Values”: The table above lists some common measurements that can aid vets in diagnosing problems involving the liver or the bile duct system. The first value, alanine transaminase (ALT, [formerly SGPT]), is an enzyme present only inside liver and muscle cells in dogs. When liver cells are injured they become “leaky,” releasing
ALT into the blood. ALT levels will rise quickly after a liver problem begins and, if the condition is reversed, they will return to normal within 1-2 weeks. The second value, aspartate transaminase (AST), is another enzyme found in liver as well as in several other organs and therefore it is less liver-specific than ALT. It will also leak into the blood after liver injury or disease, so an increase in AST will parallel that of ALT, at least in the short term. Alkaline Phosphatase (ALKP), although found in cells of several organs besides those of the liver, is another enzyme that can be an early indicator of a liver or bile duct problem if elevated in blood. An increase in ALKP without elevation of ALT, however, may suggest a non-liver problem such as Cushing’s Disease. It’s also important to know that, since ALKP is found in bone, it is normally very high in young dogs who are still growing. Bilirubin is a waste product normally excreted into the bile duct system by the liver cells. Total bilirubin (Tot BILI) is a measure of how much of this greenish waste product is circulating in the blood, where little if any should normally be found. When liver cells die or if the liver is obstructed (e.g., liver cancer), or when the bile duct is blocked (see below) and back-pressure injures the liver, bilirubin can leak into blood vessels. If bilirubin levels are high enough in the blood, its color will turn some tissues like the white of the eye or the skin yellow, resulting in jaundice (icterus). Albumin (ALB) is the main protein made by liver cells. If it is abnormally low in a blood sample, this may indicate liver disease. Finally, changes in Blood-Urea-Nitrogen (BUN) levels may also accompany liver problems. Urea is made by the liver from ammonia, a waste product of protein digestion, and excreted into blood for removal by the kidneys. If the liver is damaged, BUN levels in the blood may fall, resulting in buildup of ammonia which can spillover into blood. High blood ammonia can cause neurological signs like behavioral changes or even seizures, especially when they occur with feeding. So although not a specific “liver value”, BUN measurements can provide additional clues when liver disease is suspected. These blood tests are some of the first indicators that a vet will examine when symptoms arise which may indicate a liver problem. There are other, more specific tests that evaluate liver function and can help to pinpoint the problem, but these six basic blood values will usually be the first step in identifying liver disease or injury.
Structural Problems: The most common structural problem in the liver is called a “liver shunt” (portosystemic shunt). This is the abnormal presence of a blood vessel that allows some of the blood from the GI tract to bypass the liver and go more or less directly to the heart. This prevents some of the blood from being cleansed of toxins by the liver and also prevents the liver from acting on the nutrients carried by blood that has passed through the GI tract. Shunts can be either congenital or acquired after birth. Before birth, when the placenta manages clearance of toxins, metabolism of nutrients, etc., fetal blood bypasses the fetal liver through a shunting vessel. These prenatal shunts usually close at birth. Sometimes a fetal shunt will fail to close and remain open and functional in the pup. Or there can be abnormal, “extra” bypass vessels in pups that remain open after the normal shunt closes. In adults, acquired shunts can form when portions of the liver become so diseased that blood can no longer pass through these areas. Either way, shunts can lead to serious problems like failure of a pup to grow normally, buildup of toxins, and/or weight loss because a portion of the dog’s blood does not pass through the liver. More simple shunts can be corrected surgically, especially in pups, while others may be managed medically and some may be fatal. Other vascular abnormalities can occur in the liver, but the porto-systemic shunt is the most common.
Hepatitis: A diagnosis of hepatitis indicates that the liver is inflamed and that “inflammatory” cells from the blood and surrounding tissues have moved into the liver to combat a problem such as infection. Hepatitis can be acute, of short (leptospirosis, a bacterial infection, has begun to reappear because of possible new strains not prevented by current vaccines. There are also several fungal diseases that can cause hepatitis, but these are relatively uncommon. Another form of hepatitis, called Chronic Active Hepatitis (CAH), is actually a syndrome caused by any of a number of liver insults including but not limited to infectious agents, toxins, or genetic problems such as copper storage disease. The actual cause of CAH will often remain unidentified. In CAH, chronic liver inflammation is present, along with immune cells which produce large amounts of antibodies that eventually damage the liver cells. Later in the disease, healthy liver cells are replaced by fibrous tissue, much like cirrhosis in humans. Finally, blood flow through the liver may be compromised and shunts may form, blood pressure increases and fluid builds up in the abdomen (ascites). If the liver fibrosis is extensive, liver failure may be the end result.
Nodular hyperplasia: This condition usually appears in older dogs and can be accompanied by elevated levels of blood ALT and/or ALKP. The liver cells become enlarged and tend to accumulate fats and/or starch deposits. On ultrasound, this can mimic liver cancer and therefore biopsy of the liver is sometimes performed to rule out malignancy. The cause is unknown and liver function is usually normal.
Idiopathic Vacuolar Hepatopathy (IVH): Much like nodular hyperplasia, this condition is signaled by elevated ALKP levels without changes in other liver enzymes and without any evidence of other potential diseases such as Cushing’s. Although the cause is unclear, the findings of high ALKP and of liver vacuoles on ultrasound do not seem to predict true liver disease. Dogs with this diagnosis are usually older and generally do not develop other liver problems; this condition is diagnosed in a disproportionate number of Scottish Terriers and has led to the suggestion that this breed has a predisposition to IVH.
Hepatic cancer (neoplasm): Primary liver cancers, i.e., those which arise in the liver rather than spreading there from other parts of the body, are of several types. They can develop directly form the liver cells and be “hepatocellular” or they can form in some portion of the gall bladder. Of the two types, the latter is the less common in dogs. Again, because the liver has such a large reserve capacity, liver cancers are often diagnosed late in the disease, when much of the liver is already compromised by the cancer. In addition, liver cancers ted to metastasize to other parts of the body early in the disease, making them even more serious. In very fortunate cases where the cancer is found early and is restricted to a single liver lobe, the lobe can be surgically resected and the life span may be extended.
Biliary Disease: When bile leaves the liver, it is stored and concentrated in the gall bladder until it passes into the bile duct on its way to the intestine. The bile duct is very close to the pancreas whose duct joins it near the duodenum. So any pancreatic inflammation can put pressure on the bile duct, potentially obstructing the flow of bile. Obstruction can also occur if gallstones present in the gall bladder pass into the bile duct or if liver cancer is present and a mass presses on the duct. Early signs of biliary obstruction include difficulty in digesting fats which leads to feces that are greasy and more gray or whitish than brown. Chronic obstruction of bile flow with resulting back-pressure on the liver can result in inflammation of the liver itself, jaundice, and other problems. If severe and long-standing, obstruction can cause rupture of the duct or gall bladder, causing peritonitis or other serious conditions.
The Bottom Line: While any type of liver disease can cause serious problems for your dog, if you understand what all those tests mean, you’re in a good position to catch liver issues early and keep your dog healthy as long as possible.