Hyponatremia is classified into three categories based on extracellular fluid volume status. Which classification is associated with renal salt wasting and adrenal insufficiency?

Explanation

## Classification of Hyponatremia by Volume Status ### Three-Category System **Key Point:** Hyponatremia is classified based on **clinical assessment of ECF volume** (not serum osmolality) to guide diagnosis and management. ### Hypovolemic Hyponatremia **Definition:** Low serum Na⁺ + signs of ECF depletion (orthostasis, tachycardia, dry mucosa, low JVP, azotemia). **Common Causes:** - Renal losses: renal salt wasting, adrenal insufficiency, diuretics, osmotic diuresis - Extrarenal losses: vomiting, diarrhea, sweating, burns, third-spacing **Diagnostic Clue:** Urine Na⁺ > 20 mEq/L (renal loss) vs. Urine Na⁺ < 10 mEq/L (extrarenal loss). ### Comparison Table | Category | ECF Status | JVP | Examples | Urine Na⁺ | |----------|-----------|-----|----------|----------| | **Hypovolemic** | Depleted | Low | Renal salt wasting, adrenal insufficiency, diuretics, diarrhea | Variable | | **Euvolemic** | Normal | Normal | SIADH, psychogenic polydipsia, hypothyroidism, drugs (SSRIs, carbamazepine) | Low (< 10) | | **Hypervolemic** | Expanded | High | Heart failure, cirrhosis, nephrotic syndrome, renal failure | Low (< 10) | **High-Yield:** In **adrenal insufficiency**, cortisol deficiency impairs free water excretion AND causes renal salt wasting → hypovolemic hyponatremia. This is a classic board question. **Mnemonic for Euvolemic Causes:** **SIADH** — **S**IADH, **I**nfections (TB, meningitis), **A**dmissions (drugs), **D**isorders (hypothyroidism), **H**yponatremia. **Clinical Pearl:** The key discriminator is **clinical volume assessment** (not urine osmolality or serum osmolality). Always examine JVP, skin turgor, and orthostatic vitals first.