A 70-year-old man undergoes a routine examination and is found to have serum alkaline phosphatase levels three times higher than the normal upper limit. His serum calcium, serum phosphorus, and liver function tests are all within normal ranges. What is the most probable diagnosis?

Explanation

The patient’s elevated alkaline phosphatase with normal calcium, phosphorus, and liver function tests suggests increased bone turnover without liver involvement. Primary hyperparathyroidism commonly presents with elevated alkaline phosphatase due to increased osteoclastic activity, making it the most likely diagnosis in this scenario.