👤 By the CinnaRN Clinical Content Team🕐 Updated 2026-07-11🏷️ Physiological Adaptation🔖 Free to read, print, and share
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Use this quick-reference guide to spot, treat, and prevent SIADH (Syndrome of Inappropriate Antidiuretic Hormone) on the NCLEX. Keep it handy during review and on exam day!
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Mechanism
Key facts
↑ ADH → water retention
Dilutional hyponatremia results
Causes: SCLC, head injury, SSRIs
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Labs
Key numbers
↓ serum Na <135, ↓ osmolality
↑ urine Na, concentrated urine
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Signs
What to look for
Wt gain, NO edema, ↓ urine
Headache, confusion, seizures
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Do
Nursing actions
Fluid restrict 800-1000 mL/day
3% saline SLOW if severe
Tolvaptan, seizure precautions
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Quick Tip
Water retention causes dilutional hyponatremia with concentrated urine and dilute, low-volume serum.