DEAR DR. DONOHUE: The laboratory that analyzed my kidney stone reported it as calcium oxalate. Why didn’t the report indicate the percentages of calcium and oxalate so my diet could be modified as necessary? The general description provides no guidance to me. – J.K.

ANSWER: The percentage isn’t essential. At least 70 percent of all kidney stones are calcium oxalate, and that’s all the information necessary. The other 30 percent of stones are calcium phosphate, uric acid and ammonium magnesium phosphate. The last kind of stone is associated with kidney infections.

A piece of relevant information is how much calcium is in a 24-hour collection of urine. And knowledge of your blood calcium and phosphorus would indicate if the parathyroid glands are involved in your stone formation.

The analysis of your stone as being calcium and oxalate gives you good guidance on what you should do. The most important aspect of stone prevention is staying well-hydrated. If the urine stays dilute, stones don’t form. You should be putting out about 2.5 liters (about 2.5 quarts) of urine a day. That means you need to drink eight 10-ounce glasses of fluid daily. The rest of the needed fluid will come from fluids in solid foods. Decrease the amount of meat you eat, and cut back on salt. Both encourage calcium excretion into the urine. Obesity leads to stone formation, so if you need to, lose weight.

You don’t have to cut back on calcium, but you should keep an eye on oxalate; however, you don’t need to make a fetish of it. Oxalate-rich foods include tea, chocolate, spinach, rhubarb, beets and nuts. You should make an effort to take in more potassium, since it prevents the formation of calcium oxalate stones. Baked potatoes with skins, oranges and orange juice, bananas, peas, navy beans and squash have lots of potassium.

The most important message is the fluid message. If you drink enough that your urine is always colorless, you have lessened the chances of getting another stone.

DEAR DR. DONOHUE: I am always chewing ice. I can’t stop. I’m not going to have any teeth left. What can I do to stop this? – Anon.

ANSWER: You have pica – a compulsion to eat nonfood substances. Clay, dirt, ice, grass, starch and many other inedibles are pica foods. Children frequently eat such substances. They usually outgrow the habit or are told to knock it off. Adults can develop such cravings too. Sometimes an iron deficiency triggers them. Sometimes pregnant women start eating bizarre substances. Often there is no explanation why it happens.

The only way to save your teeth is to adopt a firm will to stop the ice-chewing. If you can picture yourself having only quarter-inch teeth, that will be a big motivation to give up this habit.

DEAR DR. DONOHUE: The only time I have incontinence is when I take a vitamin tablet. If I take my husband’s vitamin tablet, I don’t have the problem.

One of the ingredients in my vitamin is sorbitol. It doesn’t appear on the label of my husband’s vitamins. Is it, perhaps, the culprit? – J.T.

ANSWER: What kind of incontinence do you have? If it’s urine incontinence, then sorbitol is not the likely answer. If it’s bowel incontinence, sorbitol might be the reason. It gives some people diarrhea. However, the amount in one vitamin tablet is so small that it’s hard to implicate it as being the cause.

All the same, why don’t you just switch vitamins?

DEAR DR. DONOHUE: My friend was just released from the hospital after treatment for an electrolyte imbalance. What is an electrolyte? – K.R.

ANSWER: Electrolytes are atoms or molecules that have either a positive or negative charge. Sodium, potassium, chloride and bicarbonate are the body’s most important electrolytes.

Electrolytes keep the body in electrical balance, and they play a role in maintaining the body’s acid-base balance. They can be thrown out of whack for a number of reasons, like diarrhea, vomiting or kidney problems. Did your friend ever say what the underlying cause of his or her electrolyte imbalance was?

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475. Readers may also order health newsletters from www.rbmamall.com.