High alkaline phosphatase in dogs: plenty of ordinary causes

What this marker measures

Alkaline phosphatases, shortened to ALP or ALKP, are enzymes present in several tissues. The two main sources in dogs are the liver, particularly the cells lining the bile ducts, and bone that is growing or remodelling. The blood test measures total enzyme activity, all origins together. It does not say where the enzyme came from.

One canine feature changes how it reads. Dogs make an extra form under the effect of glucocorticoids, both the ones they are given and the ones their own body produces. Cats have no equivalent. The practical consequence: in dogs, ALP goes up easily, and an isolated rise is the most ordinary abnormal result on a blood panel. In cats, the same rise carries much more weight, because the enzyme's half-life there is very short and few causes push it up.

What vets look into when the value sits outside the range

The causes below are ordered by rough frequency in canine practice, not by severity.

This list is not a menu to choose from. It is the order in which the hypotheses get tested, starting with the most frequent and the easiest to check.

What this value does not tell you on its own

ALP does not measure how the liver is working. A liver working badly can have a barely raised ALP, and a dog in perfect health can have a very high ALP for a benign reason. So an isolated line neither reassures nor alarms.

The markers read at the same time:

• GGT, the other bile duct enzyme. The ALP and GGT pair helps separate a biliary origin from a rise linked to bone or to corticosteroids.
• ALT, which signals that the liver cells themselves are suffering.
• Bilirubin, which rises when bile drains badly or when red cells are being destroyed.
• Albumin, urea, cholesterol and glucose, which reflect the liver's actual work.
• Bile acids or blood ammonia, which are genuine function tests, when the question arises.
• The full blood count and electrolytes, which place the whole picture in context.

Two things are often worth more than everything else: the dog's age, and the trend. An ALP compared with a panel from six months ago tells a story; the same figure taken once tells none. An abdominal ultrasound, when it is offered, is there to look at the structure of the liver, the gall bladder and the adrenal glands, which a blood test never shows.

Finally, bear in mind that the range printed on your report belongs to the laboratory and the analyser that ran the test. Two laboratories cannot be compared line for line. Always compare a result with a result obtained by the same method.

Questions to ask your vet

1. Is this ALP isolated, or are other liver markers moving at the same time?
2. Has my dog had corticosteroids in recent months, including as an ointment or as ear or eye drops?
3. How soon should we recheck, and what will you be looking at then?
4. Would an abdominal ultrasound change what you do, and what exactly would you be looking for?
5. Are liver function tests, such as bile acids, indicated here, and what would they add that ALP does not?

Does a high ALP in my dog mean a liver problem?

Not necessarily. ALP also comes from bone, and dogs make an extra form of the enzyme under the effect of corticosteroids, whether their own or given as treatment. It is the whole panel, the dog's age and how the figure moves over time that point the way.

My puppy's ALP is above the range, is that worrying?

In a growing animal, bone makes this enzyme actively and the value often clears the range set for an adult. The vet places the result in the context of age and rechecks after growth has finished if needed.

Can an ointment or drops containing corticosteroids push ALP up?

Yes. Corticosteroids applied to the skin, the ear or the eye are partly absorbed into the circulation and are sometimes enough to raise a dog's ALP. Always tell the vet about these products, including ones given several weeks ago, and do not change anything yourself.

Should the test be repeated?

Rechecking later is a routine step, because the trend carries more information than an isolated figure. The vet sets the interval according to the dog's condition and the other markers.