FrançaisWhat ALP measures on your dog’s blood work
Alkaline phosphatase is an enzyme attached to the membranes of several tissues. Two sources matter in practice: the liver, where it lines the small channels that carry bile, and bone, where it is made by the cells that build new bone [1].
Dogs have a particularity: a third form, called corticosteroid-induced ALP. It is produced by liver cells when cortisol-like hormones are present, whether they are given as medicine or released by the body during prolonged stress or illness. Dogs are the only species known to have this form [1].
On a report you may see ALP, ALKP, SAP or AP. They all mean the same test. The result is usually given in U/L (units per litre); some European laboratories use µkat/L (U/L × 0.0167 = µkat/L) [1]. French reports call it PAL (phosphatase alcaline): see our French article on PAL and ALAT in dogs.
How to read the ALP line on the report
Each result line has five parts. Reading them in order avoids the most common mistake: comparing a number with an interval from another laboratory or a website.
- Abbreviation ALKP and ALP are the same test. Check that you are reading the dog’s chemistry panel, not a urine result.
- Result The measured activity. On its own, the number says how much enzyme is in the sample, not where it came from.
- Unit U/L here. A value in µkat/L is about 60 times smaller for the same activity.
- Laboratory interval The range of healthy adult dogs for this laboratory and this analyser. It is the only interval that applies to this result.
- Flag H means above the interval. It shows where the value sits, not why.
A useful way to describe the size of an increase is the multiple of the upper limit. In this illustrative line, 412 ÷ 212 ≈ 1.9, so ALP is about twice the upper limit. Veterinary clinical pathologists often call an increase of 2 to 3 times mild, 4 to 5 times moderate and more than 10 times marked, although cut-offs vary between clinicians [8].
ALP reference values: age and breed change the picture
There is no universal “normal ALP for dogs”. Each laboratory sets its own interval for its own method, so always use the one printed next to the result. Age and breed then shift what is expected.
| Situation | What to expect | Why |
|---|---|---|
| Puppy, young dog | ALP can be 2 to 10 times the adult value [1]. It falls during the first months and reaches adult values by about 15 months [1]. | Growing bone releases bone ALP [1, 7]. Puppies also have lower ALT than adults [3]. |
| Adult dog | Read against the laboratory’s adult interval. For example, the Merck Veterinary Manual lists 1–114 U/L [9]. | Most circulating ALP comes from the liver [1]. |
| Siberian Husky puppies | Very high values have been reported in some families, without illness [1]. | A benign, inherited increase of bone ALP [1]. |
| Scottish Terriers | Higher ALP has been reported in the breed [1]. | Mainly the steroid-induced form [1]. |
Why ALP can be high in a dog
Because ALP has several sources, a high value opens a list of possibilities that your veterinarian narrows down with the history, the examination and other results. The main families are below.
- Growth and bone. Young dogs, and situations where bone-building cells are very active [1].
- Steroid medicines. Prednisone, prednisolone and other corticosteroids increase ALP in dogs. After a single injection of methylprednisolone, the increase lasted up to three weeks in one study [1].
- Other medicines. Anticonvulsants such as phenobarbital can raise ALP [1]. In published case series, ALP rose in about a quarter of dogs given low-dose rifampicin [6] and long-term zonisamide raised liver enzymes in fewer than 10% [5].
- The body’s own cortisol. Prolonged stress, chronic illness and disorders of the adrenal glands increase cortisol, which induces the steroid form of ALP over several days [1]. Your vet may then propose an ACTH stimulation test.
- Bile flow and the liver. Anything that slows the flow of bile, inside or outside the liver, strongly induces liver ALP. Inflammation of the pancreas near the bile duct can do the same [1].
A laboratory can measure the share of the steroid-induced form, but this test is not reliable for separating the causes: any chronic disease, including liver disease, can raise it [1, 2].
What can skew an ALP result
These points explain why a vet may simply repeat the test before going further, especially when the dog is well and the increase is mild.
- A haemolysed sample (red cells broken during collection or transport) can increase measured ALP [1].
- ALP must be measured on serum or heparin plasma: a sample collected only in an EDTA tube cannot be used for this test [1].
- Medicines given in the previous weeks, including injections, tablets, creams, ear drops and eye drops: tell your vet about all of them.
- Changes of laboratory or analyser between two tests. A trend is easier to read when the same laboratory is used [1].
The values often read with ALP
ALP is rarely interpreted alone. In dogs with confirmed liver lesions, ALT, ALP or both were increased in up to 90% of cases, but these enzymes are also increased by many conditions outside the liver [4]. That is why your vet looks at the pattern.
Questions to ask your veterinarian
- How many times above the upper limit is my dog’s ALP, and how does that compare with the previous test?
- Could any medicine my dog has had in the last weeks, including creams or drops, explain the increase?
- How do the ALT, GGT and bilirubin results fit with this ALP value?
- Should we repeat the test, and when, before deciding on further tests?
- Is an ultrasound or a bile acids test useful in my dog’s case, and why?
Get your dog’s whole report explained, value by value.
ALP is one line among many. AI DiagAnimals reads the full report, with its own intervals and units, and prepares the questions to bring to your vet. The service opens soon: leave your email to be told first.
Frequently asked questions
What causes high alkaline phosphatase levels in dogs?
The most common families are growth in young dogs, corticosteroid medicines, the body’s own cortisol during prolonged stress or illness, some other medicines and conditions that slow bile flow. Your vet narrows these down with the history and other results [1].
Can stress cause elevated liver enzymes in dogs?
Prolonged stress and illness raise cortisol, and in dogs cortisol induces a specific form of ALP. This takes several days, so the stress of a single vet visit is not expected to explain a high ALP [1].
Is a high ALP normal in a puppy?
Often, yes. Growing bone releases ALP, so puppies can have values several times higher than adults until about 15 months of age [1, 3]. Your vet uses age-appropriate interpretation.
What cancers can raise ALP?
Some tumours of bone and some tumours affecting the liver or bile ducts can increase ALP [1]. A high ALP on its own cannot show whether a tumour is present: many other, more common situations raise it too.
How can I lower my dog’s ALP?
There is no treatment for the number itself. If the cause is found, the plan targets that cause. Do not stop a prescribed medicine or start a supplement without talking to your vet.
Sources
- eClinPath, Cornell University College of Veterinary Medicine. Alkaline phosphatase (ALP). eclinpath.com/chemistry/liver/cholestasis/alkaline-phosphatase
- Kojima K et al. Analysis of serum corticosteroid-induced alkaline phosphatase isoenzyme in dogs with hepatobiliary diseases. J Small Anim Pract. 2017;58(5):257-262. doi.org/10.1111/jsap.12623
- Montoya Navarrete AL et al. Effect of age, sex, and body size on the blood biochemistry and physiological constants of dogs from 4 wk to > 52 wk of age. BMC Vet Res. 2021;17:265. doi.org/10.1186/s12917-021-02976-w
- Assawarachan SN et al. A descriptive study of the histopathologic and biochemical liver test abnormalities in dogs with liver disease in Thailand. Can J Vet Res. 2020;84(3):217-224. pubmed.ncbi.nlm.nih.gov/32801457
- Smith TK et al. Incidence of hepatopathies in dogs administered zonisamide orally. J Vet Intern Med. 2022;36(2):576-579. doi.org/10.1111/jvim.16398
- Harbour L et al. Rifampicin treatment of canine multidrug-resistant meticillin-resistant staphylococcal pyoderma: a retrospective study of 51 cases. Vet Dermatol. 2022;33(5):384-391. doi.org/10.1111/vde.13105
- Hatayama K et al. Serum alkaline phosphatase isoenzymes in laboratory beagle dogs detected by polyacrylamide-gel disk electrophoresis. J Toxicol Sci. 2011;36(5):653-660. doi.org/10.2131/jts.36.653
- eClinPath, Cornell University College of Veterinary Medicine. Alanine aminotransferase (ALT). eclinpath.com/chemistry/liver/liver-injury/alanine-aminotransferase
- Merck Veterinary Manual. Serum biochemical analysis reference ranges. merckvetmanual.com/reference-values-and-conversion-tables/reference-guides/serum-biochemical-analysis-reference-ranges
Laboratory methods and reference intervals vary. This article explains; it does not diagnose. For a decision about your pet, use the original report and talk to your veterinarian. Our editorial policy.