Hypokalemia laboratory findings: Difference between revisions
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Many labs can be helpful. The transtubular potasium gradient (TTKG), urine potassium and urine chloride levels can help define the etiology of hypokalemia. | Many labs can be helpful. The transtubular potasium gradient (TTKG), urine potassium and urine chloride levels can help define the etiology of hypokalemia. | ||
== Laboratory | == Laboratory Tests== | ||
Shown below is a list of tests that can be useful in the evaluation of hypokalemia: | Shown below is a list of tests that can be useful in the evaluation of hypokalemia: | ||
* [[Complete blood count]] (CBC) | * [[Complete blood count]] (CBC) | ||
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{{Family tree/start}} | {{Family tree/start}} | ||
{{Family tree | | | A01 | | | | | A01= }} | {{Family tree | | | A00 | | | | | A00= Hypokalemia <br> [K+] < 3.5}} | ||
{{Family tree | | | |!| | | | | | }} | |||
{{Family tree | | | A01 | | | | | A01= Order: <br> 24 hours urinary K (UK)<br> Transtubular potassium gradient (TTKG)}} | |||
{{Family tree | |,|-|^|-|.| | | | | | | }} | {{Family tree | |,|-|^|-|.| | | | | | | }} | ||
{{Family tree | B01 | | B02 | | | B01= | B02= }} | {{Family tree | B01 | | B02 | | | B01= UK < 25 mEq/L <br> TTKG < 3| B02= UK > 25-30 mEq/L <br> TTKG > 7}} | ||
{{Family tree | |!| | | |!| | | | | | | }} | {{Family tree | |!| | | |!| | | | | | | }} | ||
{{Family tree | C01 | | C02 | | | C01= | C02= }} | {{Family tree | C01 | | C02 | | | C01= GI loss of potassium| C02= Renal loss of potassium}} | ||
{{Family tree | | | | | |!| | | | }} | |||
{{Family tree | | | | | C03 | | | C03= What is the blood pressure?}} | |||
{{Family tree | | | |,|-|^|-|.| | | | | }} | {{Family tree | | | |,|-|^|-|.| | | | | }} | ||
{{Family tree | | | D01 | | D02 | D01= | D02= }} | {{Family tree | | | D01 | | D02 | D01= Normal or ↓| D02= ↑}} | ||
{{Family tree | | | |!| | | |!| | | | | }} | {{Family tree | | | |!| | | |!| | | | | }} | ||
{{Family tree | | | E01 | | E02 | E01= | E02= }} | {{Family tree | | | E01 | | E02 | E01= Check the acid/base status| E02= }} | ||
{{Family tree | |,|-|^|-|.| | | | | | | }} | {{Family tree | |,|-|^|-|.| | | | | | | }} | ||
{{Family tree | F01 | | F02 | | | F01= | F02= }} | {{Family tree | F01 | | F02 | | | F01= Acidemia| F02= Alkalemia}} | ||
{{Family tree | |!| | | |!| | | | | | | }} | {{Family tree | |!| | | |!| | | | | | | }} | ||
{{Family tree | G01 | | G02 | | | G01= | G02= | {{Family tree | G01 | | G02 | | | G01= | G02= Check urinary chloride (UCl)}} | ||
{{Family tree | | | |,|-|^|-|.| | | | | }} | {{Family tree | | | |,|-|^|-|.| | | | | }} | ||
{{Family tree | | | H01 | | H02 | H01= | H02= }} | {{Family tree | | | H01 | | H02 | H01= UCL < 20| H02= UCL > 20}} | ||
{{Family tree | | | |!| | | |!| | | | | }} | {{Family tree | | | |!| | | |!| | | | | }} | ||
{{Family tree | | | I01 | | I02 | I01= | I02= }} | {{Family tree | | | I01 | | I02 | I01= | I02= }} | ||
Revision as of 21:15, 21 October 2014
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Hypokalemia laboratory findings On the Web |
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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
Overview
Many labs can be helpful. The transtubular potasium gradient (TTKG), urine potassium and urine chloride levels can help define the 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
- 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
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 mEq/L TTKG < 3 | UK > 25-30 mEq/L TTKG > 7 | ||||||||||||||||||||||||
| GI loss of potassium | Renal loss of potassium | ||||||||||||||||||||||||
| What is the blood pressure? | |||||||||||||||||||||||||
| Normal or ↓ | ↑ | ||||||||||||||||||||||||
| Check the acid/base status | |||||||||||||||||||||||||
| Acidemia | Alkalemia | ||||||||||||||||||||||||
| Check urinary chloride (UCl) | |||||||||||||||||||||||||
| UCL < 20 | UCL > 20 | ||||||||||||||||||||||||