Bit · Renal
Bartter vs Gitelman vs Liddle
Three inherited tubular disorders that all cause hypokalemic metabolic alkalosis with normal-to-low blood pressure (except Liddle). The pivot is which tubule segment is broken and what happens to calcium.
Mechanism
Each mimics a diuretic:
- Bartter — defect in the thick ascending limb (NKCC2 or its partners) → mimics a loop diuretic. Severe, presents in childhood. Hypercalciuria.
- Gitelman — defect in the distal convoluted tubule (NCC) → mimics a thiazide. Milder, presents in adolescence/adulthood. Hypocalciuria, hypomagnesemia.
- Liddle — gain-of-function in ENaC in the collecting duct → too much Na⁺ reabsorption, too much K⁺ excretion. Hypertension. Aldosterone is suppressed.
Differentiator Table
| Bartter | Gitelman | Liddle | |
| Segment | Thick ascending limb | Distal convoluted tubule | Collecting duct |
| Mimics | Loop diuretic | Thiazide | Hyperaldosteronism |
| Blood pressure | Normal or low | Normal or low | ↑↑ (HTN, often young) |
| K⁺ | ↓ | ↓ | ↓ |
| pH | Alkalosis | Alkalosis | Alkalosis |
| Ca²⁺ (urine) | ↑ (hypercalciuria) | ↓ (hypocalciuria) | Normal |
| Mg²⁺ | Normal / low | ↓↓ (hypomagnesemia is classic) | Normal |
| Renin / Aldo | ↑ / ↑ | ↑ / ↑ | ↓ / ↓ (suppressed) |
| Onset | Childhood, severe | Adolescent / adult, milder | Young HTN, family hx |
The Pivot
Three quick questions:
- Hypertension? Yes → Liddle. (Renin and aldo both low.)
- No HTN, what is urinary calcium? High → Bartter. Low → Gitelman.
- Hypomagnesemia? Strongly suggests Gitelman.
NBME-Style Stem
A 17-year-old girl presents with muscle cramps and fatigue. Blood pressure is 110/70 mm Hg. Labs: K⁺ 2.8 mEq/L, Mg²⁺ 1.2 mg/dL, bicarbonate 32 mEq/L. Urine calcium is low. Renin and aldosterone are elevated. Which of the following is the most likely diagnosis?
Concept Anchor
If a tubular disorder gives you hypokalemic alkalosis, ask first about blood pressure: high → Liddle (ENaC stuck open). If normal, calcium splits the loop (Bartter, high urine Ca) from the thiazide (Gitelman, low urine Ca) phenotype.