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Nephrology Hypokalemia Diagnosis and Testing The most common causes of hypokalemia are vomiting and diarrhea and use of diuretics. A spot urine potassium-creatinine ratio <13 mEq/g identifies hypokalemia secondary to lack of intake, transcellular shifts, or gastrointestinal losses. Other causes include: o primary aldosteronism (hypertension, urine [Cl 1 >+O mEq/L, low plasma renin activity, and elevated aldosterone level) o Barlter syndrome (normal BP, hypokalemia, metabolic alkalosis, and elevated renin and aldosterone levels) r Gitelman syndrome (normal BP, hypokalemia, and hypomagnesemia) . inhaled p2 agonists (may lead to hypokalemia in certain clinical settings) . hypokalemic periodic paralysis Hypokalemic periodic paralysis is a rare lamilial or acquired disorder characterized by flaccid generalized weakness from a sud- den intracellular potassium shift precipitated by strenuous exercise or a high carbohydrate meal. The acquired form occurs with thyrotoxicosis and is found in men of Asian or Mexican descent. lt is resolved with treatment of hyperthyroidism. Characteristic findings of hypokalemia include ileus, muscle cramps, rhabdomyolysis, and hypomagnesemia. ECGs may show U waves and flat or inverted T waves. Treatment For severe hypokalemia, IV potassium chloride is indicated. Total body potassium deficits are typically large (zoo mEq for each 1 mEq/L decrease in plasma potassium). Hypomagnesemia and metabolic alkalosis should be corrected, if present. Hypomagnesemia Diagnosis and Testing If hypomagnesemia is suspected, Iook fbr neuromuscular irritability, hypocalcemia, and hypokalemia. The most common causes of hypomagnesemia include: . GI losses (diarrhea, steatorrhea, intestinal bypass, pancreatitis) . kidney losses (loop and thiazide diuretics, alcohol induced) . medications (cisplatin, aminoglycosides, amphotericin B, cyclosporine) e hungry bone syndrome following parathyroidectomy Usually the source of hypomagnesemia is obvious. If no cause is clinically apparent, GI and kidney losses can be difterentiated by measuring the 24 hour urine magnesium excretion (elevated in kidney losses, low in GI losses). Hypomagnesemia is often associated with hypokalemia because of urine potassium wasting. Hypomagnesemia is also associated with hypocalcemia because of lower PTH secretion and end organ resistance to PTH.

Usually the source of hypomagnesemia is obvious. If no cause is clinically apparent, GI and kidney losses can be difterentiated by measuring the 24 hour urine magnesium excretion (elevated in kidney losses, low in GI losses). Hypomagnesemia is often associated with hypokalemia because of urine potassium wasting. Hypomagnesemia is also associated with hypocalcemia because of lower PTH secretion and end organ resistance to PTH. DON'T BE TRICKED . Correction of hypokalemia and hypocalcemia is difficult unless magnesium depletion is also corrected. 265