What is ALP?

The liver's share comes from the cells lining the ducts rather than from liver cells, so ALP reports on the route out of the liver, not the tissue behind it. Bone complicates that: bone-forming cells release the identical enzyme, so a change in ALP is not by itself a statement about the liver.

Bilirubin is the pigment those ducts carry, so when both markers move together the difficulty is more likely to lie in the drainage of bile than in liver cells. Calcium and Phosphate are the mineral building blocks that bone-forming cells use, and they are read alongside ALP when bone rather than bile is the question.

Anything that slows the drainage of bile prompts the duct lining to release more of the enzyme. Bone being rebuilt moves it too, and that runs fastest while a child is growing or a fracture is healing. Pregnancy contributes twice over, through bone and through the placenta, which makes ALP of its own.

ALP shifts over weeks as bile duct cells and bone-forming cells turn over, and a pregnancy or a stretch of bone growth can keep it climbing for months. A yearly measurement therefore catches a stretch of bone growth or a pregnancy while it is still running, and the next year's shows whether it has passed. This is Do Health's monitoring schedule, not a general recommendation for everyone.