Hypokalemia laboratory findings: Difference between revisions
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__NOTOC__ | __NOTOC__ | ||
{{Hypokalemia}} | {{Hypokalemia}} | ||
{{CMG}}'''; Associate Editor-In-Chief:''' {{CZ}}; '''Assistant Editor(s)-In-Chief:''' [[User:Jack Khouri|Jack Khouri]] | {{CMG}}'''; Associate Editor-In-Chief:''' {{CZ}}; '''Assistant Editor(s)-In-Chief:''' [[User:Jack Khouri|Jack Khouri]]; {{Rim}} | ||
==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 | |||
* Complete blood count (CBC) | == Laboratory Tests== | ||
* Blood urea nitrogen (BUN)/creatinine | Shown below is a list of tests that can be useful in the evaluation of hypokalemia: | ||
* Calcium | * [[Complete blood count]] (CBC) | ||
* Magnesium | * [[Blood urea nitrogen]] (BUN)/[[creatinine]] | ||
* Glucose | * [[Calcium]] | ||
* Arterial blood gases | * [[Magnesium]] | ||
* Aldosterone level | * [[Glucose]] | ||
* Renin levels | * [[Sweat chloride test]] | ||
* [[Arterial blood gases]] | |||
* [[Aldosterone]] level | |||
* [[Renin]] levels | |||
* Urinary sodium | * Urinary sodium | ||
* Urine potassium | * Urine potassium | ||
** Levels <25 meq/ | ** 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. | ** Higher potassium excretion suggest renal losses. | ||
* Transtubular potassium gradient (TTKG) | * [[Transtubular potassium gradient]] ([[TTKG]]) | ||
** TTKG= (Urine K x Plasma osmolarity)/(Plasma K x Urine osmolarity) | ** '''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 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 | ** A [[urine osmolality]] less than [[plasma osmolality]] or urine sodium <20 mEq/L, the formula is not applicable | ||
* Urine chloride | * Urine chloride | ||
** < | ** <20 meq/L: vomiting or diuretic use | ||
** > | ** >20 meq/L: [[diuretic]]s, [[Bartter's]], [[Gitelman's]], and [[mineralocorticoid]] excess | ||
==Diagnostic Algorithm== | |||
Shown below is an algorithm depicting the possible laboratory findings and their interpretation. | |||
<small><small> | |||
{{Family tree/start}} | |||
{{Family tree | | | | | | | A00 | | | | | A00= '''Hypokalemia''' <br> '''[K+] < 3.5'''}} | |||
{{Family tree | | | | | | | |!| | | | | | }} | |||
{{Family tree | | | | | | | A01 | | | | | A01= Order: <br> <div style="float: left; text-align: left; width: 12em; padding:1em;">❑ 24 hours urinary K<sup>+</sup> (U<sub>K</sub>)<br> ❑ Transtubular potassium gradient (TTKG) </div>}} | |||
{{Family tree | | | | | |,|-|^|-|.| | | | | | | }} | |||
{{Family tree | | | | | B01 | | B02 | B01= '''U<sub>K</sub> > 25-30 mEq/L/day''' <br> '''TTKG > 7'''| B02= '''U<sub>K</sub> < 25 mEq/L/day''' <br> '''TTKG < 3'''| }} | |||
{{Family tree | | | | | |!| | | |!| | | }} | |||
{{Family tree | | | | | C01 | | C02 | C01= '''Renal loss of potassium'''|C02= '''GI loss of potassium'''| }} | |||
{{Family tree | | | | | |!| | | |!| }} | |||
{{Family tree | | | | | C03 | | C04 | C03= <div style="float: left; text-align: left; width: 12em; padding:1em;">'''What is the blood pressure?''' </div>| C04= <div style="float: left; text-align: left; width: 12em; padding:1em;">Possible etiologies are: <br> [[Diarrhea]] <br> [[Laxative]]s <br> [[Villous adenoma]] </div>}} | |||
{{Family tree | | | |,|-|^|-|-|-|-|-|-|-|-|-|.| | | | | }} | |||
{{Family tree | | | D01 | | | | | | | | | | D02 | D01= Normal or ↓| D02= ↑}} | |||
{{Family tree | | | |!| | | | | | | | | | | |!| | | | | }} | |||
{{Family tree | | | E01 | | | | | | | | | | E02 | E01= '''Check the acid/base status'''| E02= <div style="float: left; text-align: left; width: 12em; padding:1em;">Possible etiologies are: <br> [[Primary aldosteronism]] <br> [[Secondary aldosteronism]] <br> Non aldosterone increase in [[mineralcorticoid]]s </div>}} | |||
{{Family tree | |,|-|^|-|v|-|-|-|.| | | | | |!| | }} | |||
{{Family tree | F01 | | F02 | | F03 | | | | F04 | F01= [[Acidemia]]| F02= [[Alkalemia]] | F03= Variable | F04= <div style="float: left; text-align: left; width: 12em; padding:1em;">Order: <br> ❑ [[Aldosterone]] <br> ❑ [[Renin]] </div>}} | |||
{{Family tree | |!| | | |!| | | |!| | | |,|-|^|-|v|-|-|.|}} | |||
{{Family tree | G01 | | G02 | | G03 | | G04 | | G05 | | G06 | | G01= <div style="float: left; text-align: left; width: 12em; padding:1em;">Possible etiologies are: <br>[[Diabetic ketoacidosis]] <br> [[Renal tubular acidosis]] </div>| G02= '''Check urinary chloride (U<sub>Cl</sub>)''' | G03= [[Hypomagnesemia]] | G04 = ↑ [[Aldosterone]] <br> ↓ [[Renin]] | G05= ↑ [[Aldosterone]] <br> ↑ [[Renin]]| G06= ↓ [[Aldosterone]]}} | |||
{{Family tree | | | |,|-|^|-|.| | | | | |!| | | |!| | | |!| | }} | |||
{{Family tree | | | H01 | | H02 | | | | H03 | | H04 | | H05 | H01= U<sub>Cl</sub> < 20| H02= U<sub>Cl</sub> > 20 | H03= [[Primary aldosteronism]]| H04= [[Secondary aldosteronism]]| H05= <div style="float: left; text-align: left; width: 12em; padding:1em;">Non aldosterone increase in [[mineralcorticoid]]s </div>}} | |||
{{Family tree | | | |!| | | |!| | }} | |||
{{Family tree | | | I01 | | I02 | I01= <div style="float: left; text-align: left; width: 12em; padding:1em;">Possible etiologies are: <br>[[Vomiting]] <br> [[Nasogastric tube]] </div>| I02= <div style="float: left; text-align: left; width: 12em; padding:1em;">Possible etiologies are: <br> [[Diuretics]] <br> [[Bartter's]] <br> [[Gitelman's]] </div>}} | |||
{{Family tree/end}} | |||
</small></small> | |||
==References== | ==References== | ||
{{Reflist|2}} | {{Reflist|2}} | ||
Latest revision as of 11:12, 6 August 2018
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Hypokalemia Microchapters |
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Hypokalemia laboratory findings On the Web |
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American Roentgen Ray Society Images of Hypokalemia laboratory findings |
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Risk calculators and risk factors for Hypokalemia laboratory findings |
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:
- 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
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 | |||||||||||||||||||||||||||||||||||||||||||