Table 6.3-1. Differential diagnosis of psychogenic, central, and nephrogenic DI using water deprivation and desmopressin stimulation

 

Psychogenic polydipsia (psychogenic DI)

Central (neurohypophyseal) DI

Nephrogenic DI

Water restriction test (fluid deprivation test)

Urine specific gravity

>1.005

<1.005

<1.005

Urine osmolality

>500-600 mOsm/kg

<250 mOsm/kg

<250 mOsm/kg

Plasma copeptin level

Initially low, then increasing

Low

High

Desmopressin stimulation test (desmopressin 1 microg SC or IV)

Urine specific gravity

No indication for the testa

Increased by ≥50%

Low, not increasing

Urine osmolality

No indication for the testa

Increase by 100% in complete central DI and 15% to 50% in partial central DI

No elevation

a As the results of the fluid deprivation test are normal.

ADH, antidiuretic hormone; DI, diabetes insipidus; IV, intravenous; SC, subcutaneous.