Kidney Stones and Idiopathic Hypercalciuria
Originally produced for “Urological” I am reposting here. This episode is keeping with the theme of kidney stone prevention.
Calcium is one of the most important minerals in the body. The average adult body contains in total approximately 1 kg of calcium, 99% of which is stored in our bones and teeth. In our bloodstream calcium also has many regulatory functions. Calcium enables our blood to clot, our muscles to contract, and our hearts to beat. Because calcium is a mineral that is so necessary for life our bodies regulate its metabolism very closely.
Our bodies cannot produce its own calcium. We get our calcium from our food. When we don’t get the calcium our bodies need in our diets, calcium is taken from our bones if our bodies need to maintain calcium balance. A lack of calcium in the diet, or disorders of calcium metabolism, can lead to osteopenia and osteoporosis.
What is adequate calcium? Around 800mg-1200mg of calcium is adequate for most healthy, active men and women. Calcium supplementation is used for patients with bone loss or at risk for osteopenia or osteoporosis.
Calcium readily binds to other minerals in the urine, combining with oxalate and phosphate to produce the common calcium oxalate or calcium phosphate stones. Calcium oxalate stones form the most common form of kidney stones. Up to 80% percent of kidney stones are calcium oxalate, either in the form of calcium oxalate monohydrate or calcium oxalate di-hydrate stones.
People with normal kidney function lose very little calcium in the urine, less than 150 mg a day, as measured by 24 urine collection. But in kidney stone formers a common finding on 24-hour urine collections is hypercalciuria, higher than normal calcium excretion. High urine calcium ‘clinical hypercalciuria’ is a urine calcium level above 200 mg/day. A person’s risk of forming kidney stones increases as the calcium levels in the urine rise.
There are a number of reasons there may be too much calcium in the urine but the most common one is idiopathic hypercalciuria. Idiopathic Hypercalciuria is not a disease per se, it is a condition and a risk factor for other diseases, kidney stones being one of them, but also long term, osteopenia and osteoporosis.
No red line determines when a patient has or needs treatment for Idiopathic Hypercalciuria. We know that values above 200mg of calcium excretion for 24 hour is a risk factor for kidney stones but historically we have used cutoffs slightly higher for patients to determine when to start or use medication, as high as 250 mg/day for women and 300 mg/day in men.
Often simple dietary changes can be enough to lower kidney stone recurrence risk in patients with only a slightly increased level of calcium in the urine. Increasing fluid intake, moderating salt, animal protein and oxalate consumption, focusing on adding fresh fruits and vegetables and adding Lemonade (often in the form of Crystal Light to decrease sugar load), orange juice or even Lemon juice to increase citrate in the urine may be all a patient needs to help prevent stone formation.
If dietary changes are not effective, however, or if the calcium excretion is very high, then medication is advised. Medication to treat idiopathic hypercalciuria to prevent kidney stones is an ongoing medication, one that is needed indefinitely.
The most common medication used for idiopathic hypercalciuria is a class of medications called thiazide diuretics, but another diuretic call indapamide can also be used.
Chlorthalidone is the most commonly used thiazide diuretic because of its long half life but hydrochlorothiazide is effective as well. Thiazide diuretics decrease the calcium levels in the urine. Dose adjustment, increasing or decreasing the dose, is done according to results on 24-hr urine testing. Repeat 24 hour urine test are needed initially to see if the medication is effective but also on an ongoing basis because some kidneys become tolerant to the medication. A short vacation from the diuretic often resets the body and resets the medication’s effects.
Thiazide diuretics can have side effects. Thiazide diuretics can be potassium wasting and cause low potassium levels in the blood. A plant based diet or increasing fruits and vegetables in the diet (I joke that I’m a fan a the banana) can increase the potassium in your diet but some patients taking the medication will need to take potassium supplements, either in the form of potassium pills or in some kidney stone formers, Potassium Citrate. Potassium Citrate has the advantage of not only preventing hypokalemia (low potassium levels) but also increasing urinary citrate excretion.
The only way to know if you need medication is to get 24-hour urine tests to determine the urine composition and excretion of calcium. If you are a person who has made lots of stones, or one very large one, or you come from a family that makes kidney stones I would suggest you ask your urologist if you might benefit from 24-hr urine testing.
