Why Are My Dog's Liver Tests Abnormal?
Dear Dr. Barchas,
Do you have any idea why my dog's liver enzyme levels are higher than normal? His diet and environment have not changed, and he doesn't exhibit any signs of illness or distress. He has itch issues, which we put down to the time of year (summer) and he's not on medications. We did blood work and all levels are good, except the liver is high. We have no clue why.
In Catch-22, Yossarian often faked a liver ailment to avoid treacherous World War II bombing missions. The reason: The liver was an incomprehensible organ, so his doctors couldn't prove he was faking.
Medical science has come a long way since then. We now understand a lot about the liver, although it is incredibly complex and undoubtedly performs a number of functions that have not yet been discovered.
The most basic purposes of the liver are to contribute to metabolism and detoxify the body by storing and producing sugar for the bloodstream. Detoxification consists of altering (metabolizing) the tens of thousands of chemicals (mostly natural, but also manmade) consumed and produced by every individual every day. These are then usually excreted by the kidneys.
The liver is one of the most important organs in the body. Because of this, there are several blood tests to check on it. However, pet owners must remember that interpretation of the tests is complex and nuanced. "Abnormal liver values" don't necessarily mean that the liver is in trouble.
First, consider that the definition of normal is arbitrary. To determine a normal reference range for a blood test, laboratories run the test on a large number of seemingly healthy individuals. They then analyze the results and usually set the "normal" range as the mean value, plus or minus one or two standard deviations. Anyone who has studied statistics will know that plenty of completely healthy people will naturally have lab values that fall outside of this range.
Second, realize that laboratory values aren't always perfect indicators of liver function. This is especially true when liver enzymes -- such as the ones mentioned by RJ -- are concerned. The enzymes in question are produced by and reside in the cells of the liver and the associated gallbladder and bile duct. When these cells are traumatized, insulted, or injured, they release the enzymes into the bloodstream, where they can be measured.
Some forms of liver injury are mild and self-limiting. A former nondrinker who goes on a weekend bender might have elevated liver enzymes on Monday morning blood tests. The liver enzymes would likely be back to normal by Friday. The same is true of a dog who is exposed to any of the millions of mildly toxic chemicals that are metabolized by the liver. Many dogs experience chronic benign (harmless) liver changes as they age; these changes can lead to consistently elevated liver enzyme levels.
Other forms of liver insult are more serious. For instance, dogs who are struck by cars may suffer bruising of the liver and increases in blood liver enzymes. Glandular disease, especially an adrenal gland problem known as Cushing's disease, can cause increased liver enzymes. Diseases of the intestines, heart, or pancreas can have secondary effects on the liver and cause blood test anomalies as well. More ominously, seriously toxic substances such as death cap mushrooms may cause liver enzyme elevations as a precursor to fatal liver failure.
Finally and unfortunately, organic liver disease can cause blood test changes. Hepatitis (viral or bacterial), gallstones and accumulations of mucus in the gallbladder, and irregular blood flow through the liver all might cause the sorts of changes that RJ describes.
Dogs with repeatedly abnormal liver enzyme results should undergo further testing. Testing of the adrenal glands, along with X-rays and ultrasound of the liver, often offer some insight into whether there is a significant problem. More advanced liver function tests also are available.
RJ, I recommend that you discuss these options with your vet.