Patient came to me with hypokalemia and hypomagnesemia. She had been asymptomatic when she underwent routine pre-op labs for an elective procedure. Her potassium was 2.0 and the magnesium was later discovered to be 0.9 mmol/L.
She had been treated for 5 months with supplemental potassium and magnesium before she found her way into my office.
During her initial work-up we found:
- Aldosterone: 61.2
- Renin: 12.4
- Trans-tubular potassium gradient: 15.98
- Diuretic screen: negative
- 24-hour urine calcium: 57 mmol
Her blood pressure was 120s over 80s on 5 mg of amiloride daily. Her volume status appeared essentially normal.
No renal vascualr disease by MRA, normal CT scan of the abdomen (no renin producing tumor). She was not on aldactone.
Diagnosis: Gitelman’s syndrome.
The principle characteristics of Gitelman’s are: low potassium, low magnesium, initially presenting in adolescence or adulthood. Patients have normal growth. Blood pressure is low. When I first learned about Bartter’s and Gitelman’s I imagined them as congentital diuretics:
- Bartter’s is congenital Lasix
- Gitelman’s is congenital HCTZ
The conditions can be understood nearly completely with this crude model. They both have low blood pressure as can be expected from a diuretic-like action. The low blood pressure triggers the renin-angiotensin-aldosterone system resulting in high plasma levels of renin and aldosteronism. In primary hyperaldosteronism, renin is suppressed.
Increased distal delivery of sodium along with increased aldosterone levels leads to increased potassium and hydrogen wasting leading to metabolic alkalosis and hypokalemia.
The two diseases differ in a few areas. Bartter’s results in decreased concentrating ability while concentrating ability is generally intact in Gitelman’s. This is predictable as the Loop of Henle is the engine which drives urinary concentrating and diluting ability. Gitelman’s has a low urinary calcium just as found with thiazides.
What was remarkable to me, was how high the aldosterone level was. This is in a patient without adrenal disease, the aldosterone is released in response to normal stimuli, volume depletion in this case. In primary aldosteronism, where there is autonomous secretion of aldosterone by a tumor, the aldosterone level typically rises to 20-30. But in this patient, where the adrenal gland is intact, the aldo level goes bonkers to almost 70.