Hypokalemia laboratory findings: Difference between revisions

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Latest revision as of 11:12, 6 August 2018

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⁺ (U_K)
❑ Transtubular potassium gradient (TTKG)

U_K > 25-30 mEq/L/day
TTKG > 7

U_K < 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

Possible etiologies are:
Diabetic ketoacidosis
Renal tubular acidosis

Check urinary chloride (U_Cl)

Hypomagnesemia

↑ Aldosterone
↓ Renin

↑ Aldosterone
↑ Renin

↓ Aldosterone

U_Cl < 20

U_Cl > 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

Template:WikiDoc Sources

@@ Line 3: / Line 3: @@
 {{CMG}}'''; Associate Editor-In-Chief:''' {{CZ}}; '''Assistant Editor(s)-In-Chief:''' [[User:Jack Khouri|Jack Khouri]]; {{Rim}}
 ==Overview==
-Many labs can be helpful. The transtubular potasium gradient (TTKG), urine potassium and urine chloride levels can help define the etiology of hypokalemia.
+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==
@@ Line 12: / Line 12: @@
 * [[Magnesium]]
 * [[Glucose]]
+* [[Sweat chloride test]]
 * [[Arterial blood gases]]
 * [[Aldosterone]] level
@@ Line 19: / Line 20: @@
 ** 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)
+* [[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
@@ Line 25: / Line 26: @@
 * Urine chloride
 ** <20 meq/L: vomiting or diuretic use
-** >20 meq/L: [[diuretic]]s, Bartter's, Gitelman's, and [[mineralocorticoid]] excess
+** >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/start}}
+{{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 | | | A00 | | | | | A00= '''Hypokalemia''' <br> '''[K+] < 3.5'''}}
+{{Family tree | |,|-|^|-|v|-|-|-|.| | | | | |!| | }}
-{{Family tree | | | |!| | | | | | }}
+{{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 | | | A01 | | | | | A01= Order: <br> ❑ 24 hours urinary K (U<sub>K</sub>)<br> ❑ Transtubular potassium gradient (TTKG)}}
+{{Family tree | |!| | | |!| | | |!| | | |,|-|^|-|v|-|-|.|}}
-{{Family tree | |,|-|^|-|.| | | | | | | }}
+{{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 | B01 | | B02 | | | B01= '''U<sub>K</sub> < 25 mEq/L''' <br> '''TTKG < 3'''| B02= '''U<sub>K</sub> > 25-30 mEq/L''' <br> '''TTKG > 7'''}}
+{{Family tree | | | |,|-|^|-|.| | | | | |!| | | |!| | | |!| | }}
-{{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 | C01 | | C02 | | | C01= '''GI loss of potassium'''| C02= '''Renal loss of potassium'''}}
+{{Family tree | | | |!| | | |!| | }}
-{{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 | | | | | C03 | | | C03= '''What is the blood pressure?'''}}
-{{Family tree | | | |,|-|^|-|.| | | | | }}
-{{Family tree | | | D01 | | D02 | D01= Normal or ↓| D02= ↑}}
-{{Family tree | | | |!| | | |!| | | | | }}
-{{Family tree | | | E01 | | E02 | E01= '''Check the acid/base status'''| E02=  Possible etiologies are: <br> [[Primary aldosteronism]] <br> [[Secondary aldosteronism]] <br> Non aldosterone increase in [[mineralcorticoid]]s}}
-{{Family tree | |,|-|^|-|v|-|-|-|.| | | }}
-{{Family tree | F01 | | F02 | | F03 |  F01= [[Acidemia]]| F02= [[Alkalemia]] | F03= Variable}}
-{{Family tree | |!| | | |!| | | |!| | | }}
-{{Family tree | G01 | | G02 | | G03 |  G01= Possible etiologies are: <br>[[Diabetic ketoacidosis]] <br> [[Renal tubular acidosis]]| G02= '''Check urinary chloride (U<sub>Cl</sub>)''' | G03= [[Hypomagnesemia]]}}
-{{Family tree | | | |,|-|^|-|.| | }}
-{{Family tree | | | H01 | | H02 | | H01= U<sub>Cl</sub> < 20| H02= U<sub>Cl</sub> > 20}}
-{{Family tree | | | |!| | | |!| | | }}
-{{Family tree | | | I01 | | I02 | I01= Possible etiologies are: <br>[[Vomiting]] <br> [[Nasogastric tube]]| I02= Possible etiologies are: <br> [[Diuretics]] <br> [[Bartter's]] <br> [[Gitelman's]]}}
 {{Family tree/end}}
+</small></small>
 ==References==
 {{Reflist|2}}