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Kidney Diseases

Urinary excretion of calcium

03/09/2011

Question:

My remaining parathyroids barely function. (Had an adenoma removed.) I presently take 1600 mg. calcium citrate daily and .25 mcg Calcitriol every other day. My serum calcium level is 8.5, which is fine; but my 24-hour urine calcium is high @281. I have read that taking more Vitamin D can help in decreasing urinary excretion of calcium? Could you comment please. I might be able to reduce the amount of calcium supplements I take. Would this be better to reduce urinary calcium excretion? I also found a few references which stated that there might be higher urinary excretion when taking calcium citrate rather than other forms of calcium. Is this true? Does potassium citrate help to reduce urinary excretion of calcium? Thank you! Mary

Answer:

A urine calcium of 281 mg per day is quite acceptable for a patient with hypoparathyroidism, and I wouldn't change a thing. If the urine calcium rose to greater than 300 mg per day then I would probably decrease your calcium intake rather than changing your vitamin D dose. In fact, an increase in your vitamin D dose would result in an increase, not a decrease, in your urine calcium. Vitamin D works by increasing the amount of calcium that is absorbed from the food in the intestines.

There should be no significant difference between taking calcium citrate and calcium carbonate (as long as the calcium carbonate is taken with food, which improves its absorption) as long as the doses are set so that an equal amount of calcium is present in the doses administered. By weight calcium citrate is only 21% calcium, whereas calcium carbonate is 57% calcium. This it takes more milligrams of calcium citrate to provide the same amount of calcium as a smaller number of milligrams of calcium carbonate.

Potassium citrate decreases the risk of kidney stones by providing citrate in the urine, which decreases stone formation. It does not, however, decrease the calcium in the urine.

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Response by:

Thomas A Murphy, MD, FACP, FACE Thomas A Murphy, MD, FACP, FACE
Associate Professor of Medicine
School of Medicine
Case Western Reserve University