Plasmatic arginine vasopressin levels in total and partial diabetes insipidus.

Plasma arginine vasopressin (AVP) was measured in 24 patients with polyuria exceeding 3.5 l/day diagnosed as severe or partial diabetes insipidus according to the dehydration test. All patients with severe diabetes insipidus diagnosed by the dehydration test had very low or undetectable basal AVP values and always subnormal plasma osmolality. Patients with partial diabetes insipidus diagnosed by the dehydration test had a wide range of AVP and osmolality values. The stimulation test performed on these patients was able to differentiate patients with primary polydipsia from patients with partial diabetes insipidus. The measurement of basal plasma AVP is capable of diagnosing all patients with severe diabetes insipidus; when we combine the stimulation test with the measurement of AVP, we can differentiate partial diabetes insipidus from other forms of polyuria.