Urine and Plasma Osmolality in Differentiation of Polyuric States

Abstract

A dehydration test relying on plasma and urine osmolality determinations is extremely helpful in differentiating various polyuric states. During a period of water deprivation, osmolality of hourly urine samples is tested until a plateau occurs. Then an injection of antidiuretic hormone is given and the response of urine osmolality determined. By this means, hypothalamic diabetes insipidus can be differentiated from psychogenic polydipsia and from nephrogenic diabetes insipidus, and degrees of antidiuretic hormone deficiency can be recognized.