A 58-year-old man with hypertension and type 2 diabetes mellitus is prescribed a thiazide diuretic. All of the following metabolic adverse effects are correctly paired with thiazide diuretics EXCEPT:

## Metabolic Adverse Effects of Thiazide Diuretics ### Correct Pairings (Options 0, 1, 3) **Option 0 — Hypokalemia:** **Key Point:** Thiazides cause hypokalemia by increasing distal tubular secretion of potassium. They block the Na⁺-Cl⁻ cotransporter in the distal convoluted tubule (DCT), leading to increased sodium delivery to the collecting duct, which enhances K⁺ secretion via the principal cells. [cite:KD Tripathi 8e Ch 15] **Option 1 — Hyperglycemia:** **High-Yield:** Thiazides impair glucose tolerance and can precipitate or worsen diabetes. Mechanisms include: - Reduced insulin secretion (direct beta-cell suppression) - Increased hepatic glucose output - Hypokalemia-induced impairment of insulin secretion This is a major concern in diabetic patients and is one reason thiazides are less favored in diabetes. [cite:Harrison 21e Ch 297] **Option 3 — Hyperuricemia:** **Clinical Pearl:** Thiazides increase serum uric acid by competing with uric acid for secretion in the proximal tubule. This can precipitate gout attacks and is a notable adverse effect, especially in patients with a history of gout. ### Incorrect Pairing (Option 2 — THE ANSWER) **Warning:** Thiazides cause **HYPOCALCEMIA**, NOT hypercalcemia. The mechanism is: 1. Thiazides block the Na⁺-Cl⁻ cotransporter in the DCT 2. This reduces the positive electrical gradient in the tubular lumen 3. The reduced lumen potential **decreases** calcium reabsorption in the DCT (calcium reabsorption is driven by the positive lumen potential) 4. Result: **Increased urinary calcium excretion → Hypocalcemia** **Note:** Loop diuretics (not thiazides) also cause hypocalcemia. In contrast, thiazides are unique among diuretics in that they **increase** calcium reabsorption in the proximal tubule and DCT under certain conditions, but the net effect is still hypocalcemia due to overall increased urinary loss. However, the statement incorrectly claims thiazides cause hypercalcemia, which is false. [cite:KD Tripathi 8e Ch 15] ### Comparison Table: Diuretic Effects on Electrolytes and Metabolites | Effect | Loop | Thiazide | K⁺-sparing | |---|---|---|---| | **K⁺** | ↓ Hypokalemia | ↓ Hypokalemia | ↑ Hyperkalemia | | **Ca²⁺** | ↓ Hypocalcemia | ↓ Hypocalcemia | ↓ Hypocalcemia | | **Mg²⁺** | ↓ Hypomagnesemia | ↓ Hypomagnesemia | ↑ Hypermagnesemia | | **Uric acid** | ↑ Hyperuricemia | ↑ Hyperuricemia | ↑ Hyperuricemia | | **Glucose** | ↑ Hyperglycemia | ↑ Hyperglycemia | Neutral | **Mnemonic:** **CHUMP** — Calcium, Hypokalemia, Uric acid, Metabolic (glucose), Phosphate — adverse effects of thiazides. (Note: Calcium is decreased, not increased.) ### Clinical Significance Thiazides are contraindicated or used with caution in: - Patients with gout (hyperuricemia risk) - Diabetic patients (hyperglycemia risk) - Patients with hypocalcemia or osteoporosis - Patients with hypokalemia Alternative agents (ACE inhibitors, ARBs, calcium channel blockers) are preferred in these populations.