What is the relation of PTH and urinary calcium level?

Answer 1

PTH is released when the body senses low serum calcium levels. PTH does everything in its power to increase serum calcium- it rips it from bone, increases its absorption from food, increases VIT D production (which also aids calcium absorption) and reduces its excretion from the body in urine. It therefore reduces urinary calcium.

Above it was stated that PTH increases vit D production.This is wrong. Exposure of the skin to sunlight when the angle isn't too low and certain foods and supplements increase vit D. When serum calcium is low, PTH is sent by the parathyroids to signal vitamin D to activate itself and enable calcium absorption. When there is sufficient dietary calcium and vitamin D, serum calcium rises appropriately, and PTH is then decreased. When there is not enough dietary calcium and vitamin D, PTH can't get the calcium it needs. PTH then goes to the kidneys to look for temporarily stored calcium. If there isn't enough there, it goes to the bone to get the calcium there. Urinary calcium is from excess calcium that is absorbed into the blood with help from vitamin D (and thyroid) or absorbed when the bone is broken down. I learned that when urinary calcium is very high (above 300), PTH is high, but serum calcium is normal, this may indicate primary hyperparathryoidism even if serum calcium is normal. Good luck finding a Doctor Who will look further into primary hyperparathyroidism for patients without high serum calcium, regardless of high PTH and high urine calcium.