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; Rim Halaby, M.D. [3]

Overview

Urinary potassium and transtubular potassium gradient are helpful to differentiate renal loss vs gastrointestinal (GI) loss of potassium. When renal loss is suspected, the assessment of the acid/base status and urinary chloride helps in determing the underlying etiology of hypokalemia.

Laboratory Tests

Shown below is a list of tests that can be useful in the evaluation of hypokalemia:

Diagnostic Algorithm

Shown below is an algorithm depicting the possible laboratory findings and their interpretation.

 
 
 
 
 
 
Hypokalemia
[K+] < 3.5
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Order:
❑ 24 hours urinary K+ (UK)
❑ Transtubular potassium gradient (TTKG)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
UK > 25-30 mEq/L/day
TTKG > 7
 
UK < 25 mEq/L/day
TTKG < 3
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Renal loss of potassium
 
GI loss of potassium
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
What is the blood pressure?
 
Possible etiologies are:
Diarrhea
Laxatives
Villous adenoma
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Normal or ↓
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Check the acid/base status
 
 
 
 
 
 
 
 
 
Possible etiologies are:
Primary aldosteronism
Secondary aldosteronism
Non aldosterone increase in mineralcorticoids
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Acidemia
 
Alkalemia
 
Variable
 
 
 
Order:
Aldosterone
Renin
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Check urinary chloride (UCl)
 
Hypomagnesemia
 
Aldosterone
Renin
 
Aldosterone
Renin
 
Aldosterone
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
UCl < 20
 
UCl > 20
 
 
 
Primary aldosteronism
 
Secondary aldosteronism
 
Non aldosterone increase in mineralcorticoids
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Possible etiologies are:
Vomiting
Nasogastric tube
 
Possible etiologies are:
Diuretics
Bartter's
Gitelman's

References