A woman has a plasma osmolarity of $300 \mathrm{mOsm} / \mathrm{L}$ and a urine osmolarity of 1200 $\mathrm{mOsm} / \mathrm{L}$. The correct diagnosis is

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[VII B; Figure 5.14]. This patient's plasma and urine osmolarity, taken together, are consistent with water deprivation. The plasma osmolarity is on the high side of normal, stimulating the posterior pituitary to secrete antidiuretic hormone (ADH). Secretion of ADH, in turn, acts on the collecting ducts to increase water reabsorption and produce hyperosmotic urine. Syndrome of inappropriate antidiuretic hormone (SIADH) would also produce hyperosmotic urine, but the plasma osmolarity would be lower than normal because of the excessive water retention. Central and nephrogenic diabetes insipidus and excessive water intake would all result in hyposmotic urine.

A Woman Has a Plasma Osmolarity Of 300mOsm/L300 \mathrm{mOsm} / \mathrm{L}300mOsm/L

A Woman Has a Plasma Osmolarity Of $300 \mathrm{mOsm} / \mathrm{L}$