Chart — Endocrine
SIADH vs Diabetes Insipidus Chart
Same hormone, opposite problems. SIADH = too much ADH (soak it up: water retained, sodium low, urine concentrated). DI = too little ADH (dump it out: water lost, sodium high, urine dilute).
Educational use only. Fluid management, sodium correction rates, and medications are provider-directed and individualized. This chart is an educational comparison aid. This material supports nursing education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional policy, or medical direction. Always follow facility protocols and current provider orders.
SIADH vs Diabetes Insipidus
| Feature | SIADH (too much ADH) | Diabetes insipidus (too little) |
|---|---|---|
| ADH | Too MUCH | Too LITTLE (or kidney unresponsive) |
| Water balance | Retains water (overload) | Loses water (dehydration) |
| Serum sodium | LOW (dilutional) | HIGH |
| Serum osmolality | Low | High |
| Urine output | Low / scant | Massive / dilute (polyuria) |
| Urine specific gravity | HIGH (concentrated) | LOW (dilute) |
| Causes | Small-cell lung CA, CNS disorders, drugs (SSRIs, carbamazepine) | Central: pituitary surgery/trauma/tumor; Nephrogenic: lithium, hypercalcemia |
| Treatment | Fluid restriction; hypertonic saline (slow) if severe; vaptans | Central → desmopressin (DDAVP); Nephrogenic → remove cause, thiazides, fluids |
| Nursing priority | Restrict fluids, watch for ↓Na neuro changes, daily weights, seizure precautions | Replace fluids, strict I&O and weights, prevent hypovolemia/hypernatremia |
Exam Traps
- ✦SIADH = too much ADH → water retention, LOW sodium, concentrated (high specific gravity) urine.
- ✦DI = too little ADH → water loss, HIGH sodium, dilute (low specific gravity) polyuria.
- ✦SIADH treatment cornerstone = fluid restriction; DI = replace fluids + desmopressin (central).
- ✦Central DI responds to desmopressin; nephrogenic DI does NOT.
- ✦Correct sodium slowly either way — daily weights and strict I&O for both.
Related Resources
Standards & sources
Fact-checked Jun 20, 2026This page is written to align with American Diabetes Association (ADA) Standards of Care · American Association of Clinical Endocrinology (AACE). It is an educational summary, not a citation of any single document — always verify specific doses, values, and protocols against current guidelines and your facility policy. How we source content →