An older adult with a history of small cell lung carcinoma reports muscle cramping, thirst, and fatigue. The primary healthcare provider diagnoses the client with a pituitary disorder and is treating the client accordingly. Which is an effective outcome of the treatment?

An older adult with a history of small cell lung carcinoma reports muscle cramping, thirst, and fatigue. The primary healthcare provider diagnoses the client with a pituitary disorder and is treating the client accordingly. Which is an effective outcome of the treatment?

• A. Urine output of 10 L/day
• B. Urine specific gravity less than 1.025
• C. Urine osmolarity of 80 mOsm/kg
• D. Serum osmolarity of 600 mOsm/kg

Answer: (B)

This question tests understanding of SIADH caused by ectopic ADH production from small-cell lung cancer and how treatment alters urine concentration. In SIADH, excess ADH makes the kidneys retain water, leading to diluted blood (hyponatremia) and concentrated urine. Effective treatment aims to reduce ADH effect so the kidneys excrete more free water, producing less concentrated urine. So an outcome where the urine becomes more dilute—reflected by a urine specific gravity less than 1.025—signals improvement and correction of the hyponatremia. The other choices don’t fit: very large urine output would suggest diabetes insipidus rather than SIADH; a urine osmolarity of 80 mOsm/kg would indicate very dilute urine, which isn’t consistent with SIADH; and a serum osmolarity of 600 mOsm/kg would be extremely hyperosmolar, not what SIADH produces.

This question tests understanding of SIADH caused by ectopic ADH production from small-cell lung cancer and how treatment alters urine concentration. In SIADH, excess ADH makes the kidneys retain water, leading to diluted blood (hyponatremia) and concentrated urine. Effective treatment aims to reduce ADH effect so the kidneys excrete more free water, producing less concentrated urine. So an outcome where the urine becomes more dilute—reflected by a urine specific gravity less than 1.025—signals improvement and correction of the hyponatremia.

The other choices don’t fit: very large urine output would suggest diabetes insipidus rather than SIADH; a urine osmolarity of 80 mOsm/kg would indicate very dilute urine, which isn’t consistent with SIADH; and a serum osmolarity of 600 mOsm/kg would be extremely hyperosmolar, not what SIADH produces.