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Potassium, Plasma / Serum

Item Value
Test Update Information Effective November 4, 2015, the potassium reference range for patients 1 year and older has been modified to 3.5-5.1 mmol/L due to changing from serum to plasma as the preferred sample type. It is known that plasma potassium levels run about 0.3 mmol/L lower than serum samples which has been verified by in house studies.
Approval req'd? No
Available Stat? Yes
Test code K
Test group Potassium
Performed by Parnassus, Mission Bay & Mt. Zion Chemistry
In House Availability Test available 24 hours per day 7 days per week
Method Ion selective electrode (ISE)
Container type Light green top preferred, Gold top acceptable
Amount to Collect 1 mL blood
Click here for Microdetermination info
Sample type Plasma or serum
Preferred volume 0.5 mL plasma or serum
Min. Volume 0.2 mL plasma or serum
Click here for Microdetermination info
Units mmol/L
Normal range
< 1 year 3.2-6.0 mmol/L
> 1 year 3.5-5.1 mmol/L

1. Normal range for infants 0 to <1 year adopted from Soldin, Steven J., "Pediatric Reference Intervals", 6th edition, AACC Press, 2007, method 4.
2. Adult range used for children >1 year old.
3. Normal range for adults was determined by testing 271 male and female healthy blood donors at UCSF with the lower limits of normal adjusted to encompass results from plasma specimens.
Critical value < 3.0 mmol/L or > 6.0 mmol/L
Synonyms K; K+; Electrolytes
Stability Room temperature 8 hours, refrigerated 2 days, frozen at -20C 1 week
Turn around times STAT 1 hour, Routine 4 hours
Additional information Hemolysis may artifactually increase the result. Levels in serum are normally 0.3 mmol/L higher than plasma levels due to liberation of potassium by platelets during clotting (c. 0.07 mmol/L per 100K platelets). Thus not only hemolysis but thrombocytosis can falsely elevate potassium levels, which can be circumvented by measuring plasma rather than serum potassium. Values < 1.5 or > 12 are automatically reassayed.
LOINC code 2823-3
Last Updated 8/6/2015 7:36:21 AM
Entry Number 766
Lab Procedure Link Click here for Procedure
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