Sign in →

Test Code LAB114 Potassium, Plasma

Performing Laboratory

St. Louis Children's Hospital Laboratory - Chemistry

Specimen Requirements

Note: This test is also available as part of LAB17, Comprehensive Metabolic Panel (CMP); LAB15, Basic Metabolic Panel (BMP); LAB16, Electrolyte Panel Lytes Pnl); and LAB19, Renal Function Panel. See Common Panel Test Combinations to avoid duplicate requests if needed.

 

Patient Preparation: None

Collection Container/Tube:

Preferred: Mint green-top Lithium Heparin (MNTGRN LiHep) tube

Acceptable: Green samplette/microtainer, plain red-top tube, or Gold SST gel tube

Submission Container/Tube: If specimen is coming from outside facility and collected in a microtainer or plain red-top tube aliquot processed sample into a plastic vial for transport (labeling with specimen type).

Specimen Collection Volume: 1.0 mL (minimum 0.6 mL)

Special Instructions: Send to lab promptly

 

Sample Rejection

Specimens collected in a Lavender-top (EDTA) tube.

Mislabled or unlabeled specimens

Logistics

Test Availability: Monday-Sunday

Cut-off time: None, performed as received

Turnaround Time: Same Day; 2 hours from receipt in performing lab

Reference Values

Reference Interval: 

Plasma (all ages) 3.3-4.9 mmol/L
Serum (all ages) 3.6-5.2 mmol/L                                                          

Critical Value: 

<1 years: <2.5  OR  ≥7.0 mmol/L
≥ 1 years: <2.5  OR  >6.5 mmol/L                                                                    
critical values are the same for both plasma and serum samples

Critical results will be called back automatically initially and every 24 hours thereafter.

 

Methodology

Ion-Selective Electrode (ISE)

Limitations

  • Hemolysis can interfer/elevate Potassium concentrations

Additional Information

FOR SLCH CORE LABORATORY USE ONLY

Lab Processing Instructions: Centrifuge to separate. If specimen is collected in microtainer or plain red-top tube aliquot sample into a Roche false-bottom tube for testing (labeling aliquot with specimen type).

Processed Volume: 0.3 mL plasma/serum

Analyte Stability:

Specimen Type Temperature Time
Whole Blood (unprocessed)  Ambient 2 hours
Plasma/Serum (processed) Refrigerated (preferred)    6 weeks   
  Ambient  7 days
  Frozen  1 year 

 

NOTE: If specimen is received in red-top (or SST gel) tube re-order as "Potassium Ser". This is required as serum reference intervals differ from plasma. 

Test Classification and CPT Code

84132

LOINC

2823-3

Last Reviewed

06/2025