Health Dictionary
Reliable, easy-to-read patient information on common medical conditions — written in plain language, free of jargon, and grounded in current evidence. Browse the most frequent diagnoses, understand what they mean for everyday life, and learn which steps and questions help you have a focused conversation with your doctor.
Hypokalemia laboratory findings
Introduction
Overview
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
Laboratory Tests
Shown below is a list of tests that can be useful in the evaluation of hypokalemia:
- Complete blood count (CBC)
- Blood urea nitrogen (BUN)/creatinine
- Calcium
- Magnesium
- Glucose
- Sweat chloride test
- 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
- <20 meq/L: vomiting or diuretic use
- >20 meq/L: diuretics, Bartter’s, Gitelman’s, and mineralocorticoid excess
Diagnostic Algorithm
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? | |||||||||||||||||||||||||||||||||||||||||||||||
| Normal or ↓ | ↑ | ||||||||||||||||||||||||||||||||||||||||||||||
| Check the acid/base status | Possible etiologies are: Primary aldosteronism Secondary aldosteronism Non aldosterone increase in mineralcorticoids | ||||||||||||||||||||||||||||||||||||||||||||||
| Acidemia | Alkalemia | Variable | |||||||||||||||||||||||||||||||||||||||||||||
| Check urinary chloride (UCl) | Hypomagnesemia | ↑ Aldosterone ↓ Renin | ↑ Aldosterone ↑ Renin | ↓ Aldosterone | |||||||||||||||||||||||||||||||||||||||||||
| UCl < 20 | UCl > 20 | Primary aldosteronism | Secondary aldosteronism | Non aldosterone increase in mineralcorticoids | |||||||||||||||||||||||||||||||||||||||||||
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Cafer Zorkun, M.D., Ph.D. [2]; Assistant Editor(s)-In-Chief: Jack Khouri; Rim Halaby, M.D. [3]