Potassium (K)

CPT Code: 



Serum or heparinized plasma 


1 mL 

Minimum Volume: 

0.5 mL 


Red-top tube, gel-barrier tube, or green-top (heparin) tube


Ion-selective electrode (ISE)


Serum is obtained by collecting blood in an untreated blood collection tube.  The sample should stand for 30 minutes to allow the clot to form prior to centrifugation.

Specimen tubes should be centrifuged unopened and the serum or plasma should be separated within one hour after venipuncture, as prolonged contact with red cells will cause elevated K+ results.

Sera or plasma separated from cells that are stored for several hours prior to analysis should be inspected for delayed fibrin clot formation.  If delayed clot formation is detected or suspected, the sample should be centrifuged before analysis.

Whole blood specimens cannot be analyzed.

HEMOLYZED SAMPLES MAY GIVE INCORRECT ELEVATED POTASSIUM RESULTS.  Intracellular potassium concentration is 30-50 fold greater than that of extracellular serum or plasma.

Reference Range:

3.5-5.1 mmol/L


Temperatures  Period 
Room Temperature  1 week 
Refrigerated (2-8 ⁰C)  1 week 



Potassium is one of the major electrolytes found primarily inside of cells. It plays a significant role in maintaining water balance inside the cells, and in functions of nervous tissue and heart and muscle contraction. 

Potassium levels are used to evaluate electrolyte balance; followed patients on diuretic therapy and with renal diseases, particularly salt-losing nephropathy; evaluate patients being treated for acidosis; prevent cardiac arrhythmias; evaluate alcoholism with delirium tremens; evaluate and treat ketoacidosis in diabetes mellitus; evaluate acid-base balance, water balance; manage intravenous therapy; evaluate anion gap; evaluate muscular weakness, leukemia, diseases of the gastrointestinal tract including laxative abuse, large villous adenomas, emesis, fistulas and tube drainage; detect, diagnose, and manage mineral corticoid excess (primary aldosteronism, Cushing syndrome, tumor with ectopic ACTH production, some cases of congenital adrenal hyperplasia); licorice ingestion.

Clinical Significance: 

Pottasium is increased in oliguria, anuria, urinary obstruction, renal failure due to shock (decreased removal of potassium), and renal tubular acidosis.

Potassium is decreased in three ways: • Inadequate intake • Excessive loss due to diarrhea or vomiting or decreased reabsorption due to increased secretion of mineralocorticosteroids • Movement into the cell as occurs with conditions causing alkalosis


Causes for Rejection: 

Hemolysis; improper labeling 

Interfering Substances:  Samples exposed to Benzalkonium salts present in certain blood catheter devices will cause falsely elevated potassium measurements.

Citrate at a test concentration of 52.9 mmol/L decreases potassium by 0.6 mmol/L.