Elevated alkaline phosphatase in dogs is a common finding when dogs undergo blood tests. In order to better understand the meaning of elevated alkaline phosphatase, it helps gaining a deeper insight into what alkaline phosphatase is and what role it plays in your dog's body. There are several potential causes for elevated alkaline phosphatase, but there are times where mild elevations may not point to anything specific unless the dog starts manifesting concerning symptoms. Following is some information pertaining elevated alkaline phosphatase in dogs.
The Role of Alkaline Phosphatase in Dogs
Alkaline phosphatase (often abbreviated as ALP or ALKP) is an enzyme that is found throughout the dog's body particularly in the dog's liver, intestines, and bones. Enzymes are simply special proteins that play a role in making special chemical reactions happen.
For instance, enzymes are capable of breaking down certain molecules into smaller parts so that these smaller molecules can aggregate together and form larger structures. In the case of the enzyme alkaline phosphatase though, its exact function still remains unknown.
It has been found that the liver and bone each produce a slightly different type of alkaline phosphatase. Also, with corticosteroids (natural or medical form), a different type is also produced. Isoenzymes is the name that is given to these variations. The isoenzyme of the liver is referred to as L-ALP, the bone isoenzyme is referred to as B-ALP and the corticosteroid isoenzyme is referred to as C-ALP.
Elevated alkaline phosphatase in dogs is often noticed when the vet runs a blood biochemistry profile which is a general blood test to check for organ function, such as the dog's liver and kidneys. When the vet runs this blood test the total sum of these isoenzymes is calculated.
A specific test for isoenzymes may be conducted in some diagnostic laboratories. This ALP isoenzyme test may be helpful in challenging cases as it can help determine the organ triggering the increased alkaline phosphatase in dogs. There are several conditions that may cause elevated alkaline phosphatase in dogs. However, things can get confusing because ALP is very sensitive but not very specific.
Problems in the Liver
In a dog with a healthy liver, alkaline phosphatase along with other substances are continuously produced and then removed from the liver through the bile ducts.
In a dog with a functionally-impaired liver from disease, the bile duct is often blocked, which leads to the retention of these substances in the liver. This causes an accumulation of alkaline phosphatase which at some point eventually seeps out into the bloodstream.
Elevated alkaline phosophatase in dogs may therefore be diagnostic for a condition known as cholestatic liver disease whichconsists of the inflammation and destruction of liver's bile ducts. Biliary stasis (bile sludging) may be seen on ultrasound.
However, a high elevation of alkaline phosophatase doesn't always mean that the dog is affected by some type of liver problem. There are several other potential causes for his elevation and usually if there is truly a liver condition at play, there would be other abnormalities in the levels of other liver enzymes such as ALT (Alanine Transaminase) and GGT (Gamma-Glutamyl Transferase). Affected dogs may also show signs of liver issues such as jaundice, changes in appetite, vomiting, lethargy, fever.
A bile acids test may be helpful, but more advanced testing may be needed such as an ultrasound of the abdomen so to look at the liver, pancreas, and the adrenal glands for signs of enlargement. A biopsy of the liver may also be insightful. In older dogs that are not showing any other high values of liver enzymes other than ALP, the increase may be due to a benign condition known ashepatic nodular hyperplasia.
Some vets may tentatively prescribe liver support supplements to take some stress off of the liver, regardless of whether an exact underlying cause for elevated alkaline phosphatase in dogs is identified or not. A liver protectant may be given for 1-2 weeks and then the bloodwork may be rechecked to see if the values are lowered.
A dog's liver is quite sensitive and may respond to any type of inflammation or infection in the abdomen by increasing its leakage of enzymes inside the blood. Generally, concerns are raised when most liver enzymes are elevated at least 4 to 6 times their normal range, explains veterinarian Dr. Kara. Because alkaline phosphatase is also produced by other tissues as well, elevated levels don't always necessarily point to a liver problem.
"In older dogs without other liver enzyme elevation it can increase due to a benign condition called nodular hyperplasia. The dog feels fine but will have hyperactive nodules on its liver producing more enzyme than needed. This can be diagnosed with an ultrasound and a fine needle aspirate of the bumps."~Dr. Kara, veterinarian
Problems in the Bones
When a dog's bones grow, they depend on alkaline phosphatase. Any conditions that involves bone growth can therefore be a cause of elevated B-ALP levels. The conditions may be normal, and therefore, benign, or there may malignant conditions at play.
Elevated ALP levels in growing puppies can therefore be considered normal as puppies are undergoing substantial bone growth. It also may be considered normal in the case of a dog sustaining a broken bone which is in the process of healing and growing new bone tissue.
However, elevated alkaline phosphatase in dogs may also be indicative of a bone infection, some type of nutritional disease impacting the bones or bone cancer. X-rays may be helpful to rule out bone cancer. In the case of bone cancer, B-ALP levels are usually mild, generally less than 4x the upper limit of normal, explains board-certified veterinarian Dr. Susan E. Johnson. At times, even arthritis or dental disease can cause elevated ALP in dogs.
Problems in the Digestive Tract
Increased ALP levels in dogs may be seen when dogs suffer from conditions such as inflammatory bowel disease (IBD). IBD in dogs may cause increased gastrointestinal noises and mild increases in liver enzymes.
In a dog with elevated alkaline phosphatase levels suffering from lip smacking, nausea, vomiting and signs of abdominal pain it may help to run a test known as canine specific pancreatic lipase (can spec PL) so to check whether pancreatitis may play a role. Pancreatitis is the inflammation of the pancreas.
In some cases, primary liver disease can trigger inflammation which may affect the pancreas as well, leading to secondary pancreatitis, or vice versa, dogs with pancreatitis develop mildly elevated liver enzymes as a response to the inflammation in the pancreas. On top of issues with a dog's pancreas, gallbladder problems can also cause elevated alkaline phosphatase in dogs.
The Effects of Drugs
As mentioned, several drugs may cause an increase in the dog's alkaline phosphatase levels. Phenobarbital may cause increased levels of L-ALP, while steroids may increase L-ALP and C-ALP levels. This increase was proven in clinical studies.
For instance, in one study, dogs were given prednisone for 10 days. When their blood was tested, it was found that just after 3 days, their alkaline phosphatase levels were already elevated with incremental increases during the 10-day period.
Even when the administration of prednisone is discontinued, the effects of steroids on a dog's liver will persist for some time (3 to 5 weeks or more).
"Alkaline phosphates (ALKP) is seen with liver, bone and sometimes intestinal issues or can be raised following the use of certain drugs an in some hormonal problems. It will also be elevated in older dogs as a normal aging change. "~Dr. Dan, veterinarian
Potential Cushing's Disease
If a dog is not taking steroids, there are chances that the elevated alkaline phsophatase may be due to increased levels of natural steroids in the body due to a disease process (specifically, excess cortisol produced by the adrenal glands) as seen in Cushing's disease (hyperadrenocorticism).
A dog suffering from this condition typically drinks large amounts of water, urinates a lot and has a ravenous appetite. This condition can be diagnosed through a test called a low dose dexamethasone suppression test (LDDS). A special urine concentration test (specific gravity) may also help the vet look for presence of isosthenuric urine (specific urine gravity in the range of 1.008-1.012)
As seen, there are several possible causes of elevated alkaline phosphatase in dogs. More potential causes include diabetes mellitus, hypothyroidism, familial hyperphosphatasemia in Siberian huskies, over-the-counter drugs or herbal supplements/ Interestingly, Scottish terriers are known to have higher ALP compared other breeds.
Sometimes, pinpointing the issue can be quite a challenge as there are many possibilities, as veterinarian Micheal Salkin points out in the quote below. Many dogs with increased ALP values act normal in every other way and their blood tests don't reveal any other abnormalities. In the case of mild elevations that are just two to three times the normal range, a wait-and-see approach may be elected in otherwise healthy dogs.
" The alkaline phosphatase is such a nonspecific enzyme that we're beginning to wonder if we should be looking at that enzyme at all.... The list of causes for elevated alkaline phosphatase is exhaustive. It takes up a half of a page in my clinical pathology text."~Dr. Michael Salkin
- Dvm360: Diagnostic approach in dogs with increased ALP activity (Proceedings)
Res Vet Sci. 2002 Jun;72(3):201-4.Duration of increased serum alkaline phosphatase activity in dogs receiving different glucocorticoid doses. Ginel PJ1, Lucena R, Fernández M.