Extra fluids prevent kidney stones

I had a kidney stone three years ago, and it was pulverized with sound waves. I had them again last year. My doctor hasn't submitted them for analysis, so I don't know the kind of stones I had. He hasn't given me any information on diet or medicine. Will you please furnish some? — S.S.

ANSWER: The most common kind of kidney stone is a calcium oxalate stone. It, like the other kidney stones, forms when urine contains too much calcium oxalate. When that occurs, crystals of this material arise, settle out of the urine and aggregate to produce a larger and larger stone. It's similar to what happens when a person adds too much sugar to iced tea. No matter how hard one stirs the tea, sugar settles on the bottom because there is too much already dissolved.

It is important to know the composition of the stone. Without such knowledge only generalizations can be made.

One of those generalizations is to stay hydrated. You should drink 2 to 2.5 liters (a little more than 2 to 2.5 quarts) of liquids a day. It doesn't all have to be water. Other liquids are acceptable. The color of your urine will tell you if you're drinking enough. It should be pale yellow or colorless.

Calcium restriction sounds like a logical approach to preventing a calcium stone; it isn't. Too little calcium increases the absorption of oxalate and promotes the growth of another stone.

You should restrict salt, however. Sodium makes more calcium and oxalate pass into the urine.

Sometimes doctors put stone-formers on diuretics (water pills), which lower the urine calcium load. Hygroton (chlorthalidone) and HydroDIURIL (hydrochorothiazide) reduce calcium excretion in the urine.

Foods high in oxalates are a stimulus for stone formation. Such foods are spinach, rhubarb, wheat bran, beets, strawberries, peanuts and beans (not lima or green beans). You don't have to ban them; just go easy with them.

DEAR DR. DONOHUE: I have ridges on my fingernails. My doctor says I am slightly anemic. My iron is 87, my percent transferrin saturation is 20 and my ferritin is 68. He prescribed a pill that contains folic acid, vitamin C and iron. My insurance won't cover it because iron can be obtained over the counter. Which type of iron should I take so that my stomach will tolerate it? — A.B.

ANSWER: The normal blood iron is 80 to 100 micrograms/ dL (14-32 mmol/L) for a man. Your reading is normal. Transferrin is a protein that transports iron in the blood. The transferrin saturation for a man ought to be 20 percent to 50 percent. Again you are OK. Ferritin is iron stored in cells. Normal values for a man are 12 to 300 nanograms/ml (12-300 micrograms/ L). Your value is acceptable. All your lab results are on the lower side of normal but still normal.

The dose of ferrous sulfate, the most commonly taken iron supplement, is 325 mg, taken three times a day. Iron is better absorbed on an empty stomach. If it causes you distress, take it with food. Ferrous gluconate has about half the iron in ferrous sulfate. Ferrous fumarate has just a bit less than does ferrous sulfate. Both are kinder to the stomach.

By ridged fingernails, do you mean elevated lines in the nail that run from the bottom to the top? They aren't a sign of iron lack. They're normal and increase with age. Iron deficiency can cause thin nails with a concavity in the center and with raised nail edges.

DEAR DR. DONOHUE: I have a question for you. I have been told that anyone with any type of cancer should refrain from sugar, as sugar helps the cancer spread. Why don't doctors tell their patients to refrain from sugar?