A 50-Year-Old Is Being Evaluated in the Office Due to Renal

A 50-year-old is being evaluated in the office due to renal stones. He states that his bowel habits change and feels constipated over the last month. He has no prior medical conditions and takes no medication. He has no family history of inherited disease. His physical examination is normal. Lab tests show normal creatine level with elevated calcium serum level 11.5 mg/dl. Further investigation reveal a PTH hormone 99 pg/ml (normal: 10-65) and phosphors inorganic level is 1.9 mg/dl Which of the following is the most likely mechanism causing this patient's low serum phosphate?

A) Decreased phosphate reabsorption in proximal tubules
B) Increased bone deposition of phosphorus
C) Increased fecal loss of phosphorus
D) Increased phosphate secretion in distal tubules
E) Transcellular shift of phosphorus into the cells