My seven year old grandson, has unusual and sometimes drastic reactions to sugars and carbs (including eye spasms). Because of this, we have removed sugar and limited carbs from his diet. He has high thirst, and frequent urination. His doctor tested his urine and found sugar and then scheduled a blood test, which was negative for diabetes. The next month, he again had sugar in his urine, but the blood test was negative, so they said they want to test his urine monthly. Why would he have sugar in his urine if he doesn’t have diabetes? Could the problem be with his kidneys or some other organ? Please respond soon. I am very concerned.

The most common cause of “sugar” in the urine is diabetes. It is a specific sugar called “glucose.” Glucose is the building block of most other sugars. For example, table sugar (sugarcane, beet sugar) is a complex of glucose plus the fruit sugar called fructose; the sugar in milk has a component of a different sugar called galactose. Special tests can help determine what type of sugar your grandchild might be “spilling” into the urine.

So while glucose in the urine certainly brings to mind the possibility of diabetes, it is not the only possibility. As you correctly concluded, there can be other possibilities, many clinically insignificant. Sometimes, an important kidney problem is discovered because of the incidental finding of “sugar” in the urine.

The kidneys tend not to “spill” glucose into the urine until the blood glucose is more than about 180 mg/dl [10 mmol/L]. So while a normal, fasting glucose (from a vein — not just a “fingerstick”) is very, very reassuring, it might be helpful for your grandchild’s doctor to also measure a fasting glucose plus a another reading about two hours after a hearty, carbohydrate filled breakfast to be even more reassured that this is not diabetes currently. A venipuncture glucose sent to the laboratory will be more accurate than a fingerstick reading on a meter.

DS