Nephrogenic diabetes insipidus laboratory findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor in Chief: Cafer Zorkun, M.D., Ph.D. [2]

Laboratory Findings

• Tests of Urine-Concentrating Ability
• Measurement of serum sodium concentration with simultaneous measurement of urine specific gravity is the most helpful screening test for diabetes insipidus.

• An increased serum sodium concentration (>143 mEq/L) in the presence of a low urine specific gravity and in the absence of excessive sodium intake, is highly suggestive of diabetes insipidus.

• The simultaneous occurrence of a high plasma osmolality and low urine osmolality reflects increased serum sodium concentration and low urine specific gravity.

• Failure to concentrate the urine normally in the presence of high plasma vasopressin concentration and in the presence of parenteral administration of vasopressin or desmopressin (DDAVP) is diagnostic of NDI. Administration of 10 to 40 μg DDAVP intranasally in individuals older than age one year usually results in a urine osmolality that is:

• Greater than 807 mOsm/kg in normal individuals
• Less than 200 mOsm/kg in individuals with NDI [van Lieburg et al 1999]

Note: The results of these tests may be difficult to interpret in individuals with "partial diabetes insipidus," which results from either subnormal amounts of vasopressin secretion (partial neurogenic DI) or partial response of the kidney to normal vasopressin concentrations (partial nephrogenic DI). These two disorders can be distinguished by comparing the ratio of urine osmolarity to plasma vasopressin concentration against normal standards.