Hypokalemia laboratory findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]; Assistant Editor(s)-In-Chief: Jack Khouri

Overview

Many labs can be helpful. The transtubular potasium gradient (TTKG), urine potassium and urine chloride levels can help define the etiology of hypokalemia.

Laboratory Findings

• Complete blood count (CBC)
• Blood urea nitrogen (BUN)/creatinine
• Calcium
• Magnesium
• Glucose
• Arterial blood gases
• Aldosterone level
• Renin levels
• Urinary sodium
• Urine potassium
  • Levels <25 meq/day (or <15 meq/L on urine spot) rule out a renal cause of hypokalemia and suggest extrarenal potassium loss or transcellular shift
  • Higher potassium excretion suggest renal losses.
• Transtubular potassium gradient (TTKG)
  • TTKG= (Urine K x Plasma osmolarity)/(Plasma K x Urine osmolarity)
  • A TTKG less than 2-3 indicates renal potassium conservation in a hypokalemic patient
  • A urine osmolality less than plasma osmolality or urine sodium <20 mEq/L, the formula is not applicable
• Urine chloride
  • <25 meq/L: vomiting or remote diuretic use
  • >40 meq/L: diuretics, Bartter's, Gitelman's and mineralocorticoid excess

References

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