Drinking more than three liters a day with a corresponding increase in urinary excretion is considered too much. This so-called “polydipsia-polyuria syndrome” usually develops over time as a habit or is a side effect of a mental illness.
In rare cases, however, the cause may be a deficiency of the hormone vasopressin (AVP; AVP deficiency, formerly known as central diabetes insipidus). In this disease, the pituitary gland lacks the hormone AVP, which regulates water and salt levels in our body. Affected people cannot concentrate their urine and lose large amounts of fluid. Therefore, they have a strong sense of thirst and must drink a lot to avoid dehydration.
Vasopressin
The distinction between a “harmless” form of excessive drinking, also called primary polydipsia, and AVP deficiency is extremely important because the treatment is fundamentally different. AVP deficiency is treated with the hormone vasopressin, while people with primary polydipsia receive behavioral therapy aimed at slowly reducing the amount they drink.
Incorrect treatment can have life-threatening consequences, as incorrect treatment with vasopressin can lead to water intoxication. And conversely, drinking less in AVP deficiency will lead to dehydration.
In recent years, researchers at several international teaching hospitals have worked intensively on testing methods to distinguish between these two syndromes. A test in which the hormone vasopressin is stimulated by saline infusion showed a very high reliability of 97%. However, because of the strong salt increase, constant monitoring of patients and half-hourly blood salt measurements are necessary. The same researchers therefore developed a simplified and well-tolerated test in which, instead of the salt infusion, an infusion containing the protein component arginine, which also stimulates the hormone vasopressin, is administered. This test showed equally good reliability.
Gold standard
The new study directly compared the two tests. The results of the international study, in which seven tertiary hospitals participated, showed that the saline stimulation test is clearly better and more reliable than the arginine infusion test. In the future, therefore, the saline stimulation test should be the “gold standard,” while the arginine stimulation test should come in second place.
