Dr. Greene's Answer
If your daughter was dehydrated at the time of the test, this could have caused the calcium oxalate crystals – but if they are found again it’s worth paying a bit of attention,, because kids who have ongoing high levels of oxalate in the urine are more likely to develop kidney stones later on in life.
Oxalate is found in many foods, and oxalate levels in the urine can often be decreased by changes in the diet. Your daughter may not need to do any of these things, but I’m including them here for reference.
1) Increase fluids. Pretty much any fluid helps, with the exception of grapefruit juice, which doesn’t seem to help and may even raise the risk of stones. And because your daughter hadn’t been drinking much at the time of her urine test, staying well hydrated may be important for her.
2) Avoid high animal protein diets. Animal protein as part of a balanced diet is fine, but a diet that focuses on large amounts animal protein can increase oxalate.
3) Increase (most) fruits and vegetables in the diet. This decreases oxalate in the urine, probably from the extra potassium and citrate, among other things.
4) Decrease high oxalate foods. Spinach and rhubarb are the classics, but some nuts and legumes are also pretty high.(Check Harvard’s spreadsheets with the oxalate concentration of foods for a detailed list. Many of these are healthy foods, so I wouldn’t even think about decreasing them unless someone is having a problem. If it were ever an issue, there are low-oxalate alternatives to all of the high-oxalate foods (like choosing chicken noodle soup instead of lentil soup, or oatmeal instead of Cream of Wheat).
5) Limit added sodium in processed foods.
6) Limit added sugar and high fructose corn syrup in foods.
7) Encourage foods that contain calcium.
8) Avoid calcium supplements and high-dose vitamin C supplements.
Again, someone with oxalate crystals may not need to do any of these things in the short run. They may never have this result again. But either way, increasing fluids, fruits and vegetables, and calcium-rich foods and also decreasing added sodium, sucrose, and high fructose corn syrup are good for all of us (and each also happens to reduce oxalate levels and/or stone risk).