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Polyuria is a condition in which the body produces unusually large volumes of urine at abnormally frequent intervals. Diabetes and polyuria are linked because polyuria is one of the main symptoms of diabetes. While it is also associated with other medical problems, polyuria is a symptom of both diabetes mellitus and the lesser known, and quite different, diabetes insipidus. Polyuria occurs in both forms of diabetes mellitus, Types 1 and 2. If any of the varieties of diabetes are left untreated, polyuria can lead to severe dehydration, which could be serious in frail or elderly patients.
In diabetes mellitus, the level of sugar in the blood is too high. Normally, when the kidneys filter blood to make urine, they reabsorb all of the sugar, returning it to the blood stream. The sugar levels associated with diabetes mellitus are so high that they overwhelm the kidneys' ability to reabsorb it, with the result that sugar ends up in the urine. This sugar draws more water into the urine and that is how the large urine volumes seen in diabetes and polyuria occur.
The mechanism that causes polyuria in diabetes insipidus is different. Here, the problem does not concern blood sugar levels. Instead, there is an abnormality regarding the hormone which acts on the kidneys to make them preserve water in the body.
This water-conserving hormone is produced and stored in the brain. Some forms of brain damage, which could be caused by disease or accidental injury, can reduce the amount of hormone available. As a result, the kidneys fail to conserve water, allowing large amounts to pass out of the body in the form of very dilute urine. Another form of diabetes insipidus develops because the kidneys do not respond to the hormone. This can be inherited or it may result from kidney damage, sometimes caused by certain drugs.
Along with polyuria, one of the other signs of diabetes can be an extreme thirst, known as polydipsia. The two conditions often occur together and may be associated with dehydration. If a patient is excessively dehydrated, treating diabetes and polyuria may involve admission to the hospital so that fluids can be given. Otherwise, management of both diabetes and polyuria involves giving the appropriate treatment for the specific type of diabetes.
Diabetes mellitus Type 1 is generally treated with insulin, which enables sugar to be taken up out of the blood stream into cells. Type 2 can often be controlled by making dietary changes and exercising more, although medication is required in some cases. Diabetes insipidus may be managed by giving an artificial version of the missing hormone if appropriate, or by giving other medications.