In primary hypoparathyroidism, which lab pattern is expected?

In primary hypoparathyroidism, which lab pattern is expected?

• A. PTH low; serum Ca low; vitamin D low; phosphate high
• B. PTH high; Ca high; vitamin D high; phosphate low
• C. PTH low; Ca low; vitamin D low; phosphate high
• D. PTH high; Ca low; vitamin D low; phosphate high

Answer: (C)

PTH is the hormone that raises serum calcium and lowers serum phosphate by acting on bone, kidney, and the activation of vitamin D. In primary hypoparathyroidism, there is a deficiency of PTH, so these actions are lost. Without PTH, calcium release from bone and calcium reabsorption in the kidney are reduced, leading to hypocalcemia. The activation of vitamin D in the kidney also falls because PTH stimulates 1-alpha hydroxylase; with less active vitamin D, intestinal calcium absorption decreases, worsening low calcium. At the same time, PTH normally promotes phosphate excretion in the kidney; without it, phosphate reabsorption increases, causing hyperphosphatemia. So the expected pattern is low PTH, low calcium, low active vitamin D, and high phosphate.

PTH is the hormone that raises serum calcium and lowers serum phosphate by acting on bone, kidney, and the activation of vitamin D. In primary hypoparathyroidism, there is a deficiency of PTH, so these actions are lost. Without PTH, calcium release from bone and calcium reabsorption in the kidney are reduced, leading to hypocalcemia. The activation of vitamin D in the kidney also falls because PTH stimulates 1-alpha hydroxylase; with less active vitamin D, intestinal calcium absorption decreases, worsening low calcium. At the same time, PTH normally promotes phosphate excretion in the kidney; without it, phosphate reabsorption increases, causing hyperphosphatemia. So the expected pattern is low PTH, low calcium, low active vitamin D, and high phosphate.