Hypokalemia laboratory tests

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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

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