Neurogenic polydipsia FIGURE 64.1 Diagnostic approach to a child with polydipsia UA, urinalysis; BUN, blood urea nitrogen; Cr, creatinine; Ca, calcium TABLE 64.2 COMMON CAUSES OF POLYDIPSIA Diabetes mellitus Sickle cell anemia Diabetes insipidus (antidiuretic hormone deficient) Patients suspected of having primary polydipsia, DI, and nephrogenic DI require further testing that can be dangerous Because these tests need to be performed in a closely supervised, controlled setting, these patients should be admitted for evaluation Patients with primary polydipsia should respond to a water deprivation test by increasing their urine-specific gravity and osmolality Patients with DI and nephrogenic DI should have rapid weight loss while continuing to excrete urine