To distinguish Diabetes Insipidus from cause excessive urination other then blood glucose levels, levels of bicarbonate, and calcium levels, need to be tested. Measurement of blood electrolytes can reveal a high sodium level (hypernatremia as a marker of the degree of dehydration). Urinalysis showed dilute urine with a low specific gravity. Urine osmolarity and electrolyte levels are usually low.
A fluid deprivation test helps determine whether diabetes insipidus is caused by:
Excessive fluid intake (primary polydipsia)
defects in the production of ADH
defects in the renal response to ADH
This test measures the changes in body weight, urine output, and urine composition when fluids are retained and when dehydration occurs. The body's normal response to dehydration is hold urine and conserve water, so that the urine becomes more concentrated and urination becomes more frequent. Patients with diabetes insipidus continue to urinate large amounts of dilute urine although not drink any liquid. In primary polydipsia, urine osmolality increases and stable above 280 Osm / kg with fluid restriction, while stabilization at lower levels indicate diabetes insipidus. Stabilization in this test means, especially when the increase in osmolality less than 30 Osm / kg per hour for at least 3 hours. Measured levels of ADH during this test is also required, although it would be time consuming to do so. [3]
To differentiate the type of Diabetes Insipidus, desmopressin stimulation is also used, desmopressin can be done by injection, nasal spray, or tablet. At the time of use of desmopressin, the patient should drink fluids or water only when thirsty and not at other times, as this may cause a sudden fluid accumulation in the central nervous system. If desmopressin reduces urine output and increases osmolarity, the pituitary production of ADH is reduced, and the kidneys will work normally. If diabetes insipidus is due to renal pathology, desmopressin does not change either urine output or osmolarity.
If suspected central diabetes insipidus, other pituitary hormone tests such as an MRI test, is required to determine whether there is a disease process (such as a prolactinoma, or histiocytosis, syphilis, tuberculosis or other tumor or granuloma) that affect fungsihipofisis Most people with this type of disorder have experienced trauma head in the past or who have stopped ADH production because of unknown cause.
Drinking habits (in the worst condition known as psychogenic polydipsia) is the most common type of diabetes insipidus for all ages. While many adult cases in the medical literature related to mental disorders, most patients with habit polydipsia (drink much) has no other detectable disease. This difference is known for patients undergoing test water restrictions, as several levels of urinary concentrations above isosmolar usually obtained before the patient becomes dehydrated.
