ALP

In dogs, the differential for a raised ALP is famously broad. Common, often benign causes sit alongside important ones:

• Steroids and steroid-like effects — corticosteroid medicines, and the natural excess of Cushing's disease, induce a specific ALP in dogs. This is one of the commonest reasons for a high ALP.
• Bile-flow problems (cholestasis) — gallbladder disease, bile-duct obstruction, or liver disease crowding the ducts.
• Bone activity — growing puppies normally have high ALP; bone disease can raise it in adults.
• Other endocrine and reactive causes.

Because of this range, a raised canine ALP is interpreted by its company: with a raised ALT it leans hepatocellular; with a raised GGT it leans towards the bile system; in a dog with increased thirst, a pot-belly and skin changes it raises Cushing's. The magnitude and the trend help, but ALP almost never stands alone.

A normal ALP is reassuring, and a low ALP is generally not a concern. In dogs, because ALP is so easily raised by benign factors, a normal ALP alongside a raised ALT can itself be a useful clue about which process is at play.

Followed over time, ALP is useful for tracking cholestatic (bile-flow) liver disease and monitoring response to treatment. A persistently high or rising ALP, especially with a rising GGT and bilirubin, points to an ongoing bile-system process worth investigating; a falling ALP tracks resolution. In a dog on steroid medication, a stable, steroid-induced elevation is expected and interpreted in that light rather than as new disease.

This is a marker where species matters enormously. Cats have far less ALP in their tissues and it clears from the blood quickly, so cats do not show the big steroid- and bone-driven rises dogs do. The practical result: almost any elevation of ALP in a cat is clinically significant, and often points to important liver disease such as hepatic lipidosis or cholangitis, or to hyperthyroidism. A modestly high ALP that might be shrugged off in a dog demands attention in a cat.

ALP is measured on a routine chemistry panel, reported in U/L. No special preparation is needed; a fasting sample reduces interference. Reference ranges vary between labs and analysers, and puppies run much higher than adults, so always read the value against your own report's range and interpret it with age and species in mind.

A mildly raised ALP in an otherwise-well adult dog is often observed and rechecked, particularly if ALT is normal and there is a benign explanation like recent steroids. A markedly or persistently raised ALP — or any clear elevation in a cat — warrants a fuller look with your vet: ALT, GGT and bilirubin to localise it, imaging of the liver and gallbladder, and, where the picture fits, screening for Cushing's or thyroid disease.