By Dr. Becker
Many conscientious pet owners take their furry charges in for regular wellness exams, including organ function tests. These owners are often concerned, or at least curious about changes in the numbers from one blood test to the next – especially when the changes relate to major organs like the liver. Most knowledgeable pet guardians are very aware of how important liver function is to their animal’s health, longevity, and quality of life.
Changes in liver enzyme values from one blood test to the next are actually quite common, and elevations in liver enzymes don’t automatically indicate organ disease. While any abnormal value should be addressed, there are several factors to consider when reviewing test results. These include which liver values have increased, how much they’ve increased, and how long the elevation has persisted. This is one reason I suggest you ask your veterinarian to go over test results with you in the exam room, or ask for a copy of the results and review them at home, adding them to your pet’s medical file so you can compare them to future test results.
There are a number of blood serum chemistry values your veterinarian uses to determine how well your dog’s or cat’s liver is functioning. The values most commonly measured include ALP (alkaline phosphatase), ALT (alanine transaminase), AST (aspartate transaminase), bilirubin and albumin.
Elevations in Alkaline Phosphatase (ALP)
It’s not unusual for a young pet’s ALP enzyme to be elevated, but it’s frustrating to me how many vets assume this marker isn’t relevant unless the animal is showing clinical signs. I’m a stickler for perfect bloodwork, or I want a reason for why it’s not. Ignoring subtle changes in an animal’s biochemistry profile usually means the animal is slipping away from homeostatic balance, something that should not be overlooked year after year.
The ALP enzyme is produced in several places in the body, including the outer layer of liver cells in response to stress. An elevated ALP can certainly be an early marker for liver disease, but it can also point to problems outside the liver – or it can be a transient, self-resolving situation.
For example, within a few hours of ingesting colostrum, puppies and kittens have very high levels of ALP. Young pets are also apt to have high levels of ALP in their bones. Diseases of the bones, endocrine system, cancer and other disorders can also increase ALP levels. When some drugs such as certain types of glucocorticoids, as well as anticonvulsants are given, a process called “enzyme induction” takes place. Dogs with hyperadrenocorticism, which causes increased cortisol levels, also have higher ALP levels.
So although ALP is used primarily as an indicator of liver disease, there are many other potential sources of elevation to consider.
Elevations in Alanine Transaminase (ALT)
If an animal’s ALT level is elevated, it’s cause for concern. ALT is produced inside liver cells and the only way it can reach the bloodstream is through a ruptured cell. So an elevated ALT value (without elevation in other markers) may indicate rapid death of, or injury to, liver cells.
However, the liver has regenerative powers, so slightly higher than normal rates of cell death, or short periods of significant cell death, may be resolved by the liver’s ability to regenerate tissue. As a general rule, veterinarians consider that ALT values two to three times normal warrant further investigation, while lower elevations in a clinically normal animal can be closely monitored through regular rechecks.
Also, ALT is present in intestinal as well as liver cells, so a serious GI disease can cause mild elevations in this enzyme.
Elevations in Aspartate Transaminase (AST)
AST is a more sensitive marker, but less specific than ALT for identifying liver disease. AST is found not only in the liver, but also in the skeletal and cardiac muscles, so it’s important to investigate the source of any elevation in this enzyme.
Elevations in Bilirubin
An elevation in a pet’s bilirubin level may be a sign that several significant and life threatening issues could be occurring, including liver or obstructive gallbladder disease. If the animal is sick, immediate diagnosis and treatment is required. Bilirubin is a pigment released when red blood cells die off. In a healthy animal, bilirubin is produced more or less continuously as old blood cells are replaced with new ones, and the liver is able to clear the waste pigments.
In some animals with normal liver function, bilirubin may be elevated by a disease that causes rapid destruction of red blood cells. While the liver may be healthy, the disease causing the death of red blood cells (including auto immune issues, heavy metal accumulation, toxins, parasites or infectious disease) needs to be immediately diagnosed and treated.
Low Levels of Albumin
A low albumin level in a dog or cat can also signal liver failure. Albumin is a blood protein produced by the liver, and a low level can also point to potential kidney disease, malabsorption of nutrients from food, intestinal disease, or inadequate nutrition.
Low albumin should be investigated, especially in pets that appear well nourished.
Diagnosing Liver Disease
The liver has tremendous regenerative capacity and the ability to adequately function even when it is “sick,” so an elevated blood ALT or AST level does not necessarily correlate to the relative “sickness” of the liver. That’s why these values, while important, don’t give a complete picture of the health of the organ. In fact, ALT and AST elevations can be quite minor in animals with end-stage liver disease.
In light of this, it’s important to never rely on a single ALT or AST value to arrive at a definitive diagnosis or prognosis. Increased ALT or AST values should be rechecked regularly, along with other markers of liver disease and liver function.
Since a definitive diagnosis of liver disease often requires a biopsy, many veterinarians faced with abnormal liver values in a pet, first try to rule out non liver-related diseases that might contribute to the abnormal values.
Abnormal liver enzymes signal there is liver damage occurring, but they aren’t a measure of liver function or health. The two-part blood test that measures liver function is called a Bile Acids Test, and it is the test I recommend if liver enzymes continue to climb, or if the patient is symptomatic.
If all other potential conditions are eliminated, the next step is typically to do an ultrasound exam of the liver, the gallbladder, and surrounding tissues.
If your pet is seriously ill and/or other diagnostic tests return ambiguous results, unfortunately, a liver biopsy may be the only remaining option to accurately diagnose your four-legged family member’s condition, and evaluate available treatment options. I always try to avoid this invasive procedure if possible, but sometimes it’s the only way to diagnose certain liver diseases.
Recheck, Recheck, Recheck
If your pet isn’t showing any signs of illness and mildly elevated liver enzymes are identified on routine bloodwork, your vet may suggest offering a means of liver detoxification, including milk thistle, SAMe, Phosphatidyl choline, NAC (N-acetyl cysteine) or SOD (superoxide dismutase). Hopefully, he or she will also address potential external causes of liver stress, including air, water and food contaminants, environmental chemical and toxin loads, infectious diseases, unnecessary vaccine stress, and parasite infestations. Sometimes a temporary liver detox diet can be of benefit.
If your pet has no symptoms of disease and you opt to provide a holistic liver support protocol, rechecking liver enzymes to ensure they’ve returned to normal is important for your peace of mind and to identify progressive liver disease before a crisis occurs. If your pet is ill, identifying the root cause (including infectious disease, metal accumulation, degenerative, inflammatory or immune-mediated disease or a congenital/structural problem) will allow your vet to formulate the best treatment protocol as early as possible, giving your furry friend the best chance for a speedy recovery and a good quality of life.