What is your approach to isolated alkaline phosphatase without other laboratory abnormalities?

Assuming none of the other LFTs are abnormal, I would get a GGT.

If GGT is elevated --> likely a hepatobiliary issue. Would consider age, medical history, and risk factors. If persistently elevated, could consider RUQ US + MRCP. Conditions like PSC or PBC are frequently discovered due to asymptomatic alkaline phosphatase elevations.

If GGT is not elevated, consider a bone issue --> consider bone scintigraphy or other imaging modalities. Could consider Paget's vs. other osteoclastic/osteoblastic diseases, like breast/prostate cancer.

Hard to give further guidance without more details, but this is a general framework to consider.