Following are differential diagnoses for patients presented with elevated ALP.
Cholestasis (intrahepatic or posthepatic)
Hepatic lipidosis (cats)
Diabetes mellitus
Hyperadrenocorticism
Neoplasia of liver or biliary tree
Infectious (eg, ascending intestinal bacteria, leptospirosis, histoplasmosis, toxoplasmosis) or inflammatory (eg, idiopathic, copper storage) hepatitis
Cholecystitis or cholangitis
Triaditis (ie, concurrent pancreatitis, cholangiohepatitis, and inflammatory bowel disease [cats])
Gallbladder mucocele
Pancreatitis
Portosystemic shunt
Portal vein hypoplasia
Toxicity (eg, tetracyclines, NSAIDs)
Nodular hyperplasia
Hepatic fibrosis
Proximal duodenal obstruction (eg, mass or foreign body causing secondary bile duct obstruction)
Reactive hepatopathy (eg, enteritis, chronic enteropathy)
Induction by drugs or hormones (independent from toxicity)
Phenobarbital
Glucocorticoids (dogs)
Hyperthyroidism
Hypothyroidism (usually mild elevation, if any)
Other
Increased osteoblastic activity (eg, osteosarcoma, hyperparathyroidism, bone fracture or damage, hyperthyroidism)
Normal bone growth (young dogs)
Breed-specific conditions (eg, high ALP in Scottish terrier, benign familial hyperphosphatemia in Siberian husky)