with a low specific gravity They may become severely dehydrated if the weight loss is in excess of 3% to 5% Constant observation should be maintained during the water deprivation test to ensure patients not covertly consume water and to prevent severe dehydration A trial of intranasal desmopressin (DDAVP) should distinguish between DI and nephrogenic DI because patients with antidiuretic hormone–deficient DI will respond to the exogenous hormone Unfortunately, even these tests are fraught with inaccuracies Patients with primary polydipsia who have chronic overhydration and diminished capacity to concentrate urine may have a blunted response to water deprivation In addition, patients with DI and nephrogenic DI may produce hypertonic urine if the glomerular filtration rate is decreased as severe dehydration ensues Radioimmunoassay for antidiuretic hormone can be helpful in confusing cases TABLE 64.3 LIFE-THREATENING CAUSES OF POLYDIPSIA Diabetes insipidus (antidiuretic hormone deficient) Nephrogenic diabetes insipidus Diabetes mellitus Primary polydipsia Suggested Readings and Key References Cermeroglu AP, Buyukgebiz A Psychogenic diabetes insipidus in toddlers with compulsive bottle-drinking: not a rare entity J Pediatr Endocrinol Metab 2002;15(1):93–94 Dabrowski E, Kadakia R, Zimmerman D Diabetes insipidus in infants and children Best Pract Res Clin Endocrinol Metab 2016;30(2):317–328 Di Iorgi N, Allegri A, Napoli F, et al Central diabetes insipidus in children and young adults: etiological diagnosis and long-term outcome of idiopathic cases J Clin Ednocrinol Metab 2014;99(4):1264–1272 Dundas B, Harris M, Narasimhan M Psychogenic polydipsia review: etiology, differential, and treatment Curr Psychiatry Rep 2007;9(3):236–241 Kavanagh C, Uy N Nephrogenic diabetes insipidus Pediatr Cl N Am 2019;66(1):227–234 Rose S, Auble B Endocrine changes after pediatric traumatic brain injury Pituitary 2012;15(3):267–275