A 72-year-old man with chronic kidney disease (CKD) presents for follow-up. His laboratory results show a serum creatinine of 2.5 mg/dL, urea of 40 mg/dL, elevated phosphate, and low calcium. What is the most likely cause of his abnormal calcium and phosphate levels? A) Hyperparathyroidism B) Osteomalacia C) Chronic kidney disease D) Paget’s disease E) Hypervitaminosis D Correct Answer: C) Chronic kidney disease Explanation: Chronic kidney disease (CKD) leads to elevated phosphate and low calcium levels due to impaired renal excretion of phosphate and reduced activation of vitamin D, which reduces calcium absorption in the gut. Hyperparathyroidism (A) can also cause elevated phosphate, but it typically presents with hypercalcemia (not low calcium). Osteomalacia (B) is due to vitamin D deficiency and results in low calcium and low phosphate, but it is not typically associated with elevated creatinine or urea. Paget’s disease (D) presents with bone deformities, elevated alkaline phosphatase, and normal calcium and phosphate levels. Hypervitaminosis D (E) would cause hypercalcemia and normal or low phosphate. Key Tips for PLAB 1: ✅ Chronic kidney disease leads to hyperphosphatemia and hypocalcemia. ✅ Management of CKD often includes phosphate binders and vitamin D supplements.
