A 55-year-old female presents with polyuria, polydipsia, and nocturia. Laboratory tests

A 55-year-old female presents with polyuria, polydipsia, and nocturia. Laboratory tests

A 55-year-old female presents with polyuria, polydipsia, and nocturia. Laboratory tests show elevated serum osmolality and dilute urine. What is the most likely diagnosis?

A. Diabetes mellitus

B. Diabetes insipidus

C. Syndrome of inappropriate antidiuretic hormone (SIADH)

D. Chronic kidney disease

E. Hypothyroidism

Answer: B

Explanation: Diabetes insipidus is characterized by polyuria (excessive urine output), polydipsia (excessive thirst), and nocturia, due to a deficiency of antidiuretic hormone (ADH) or resistance to ADH. Laboratory findings include elevated serum osmolality and dilute urine (low urine osmolality).