- K+ (Potassium, Serum)
- Serum potassium
- Red or tiger top, or gel barrier tube
- Green top tube may be used in conditions associated with thrombocytosis
- 5-7 mL of venous blood
Additional information
- Blood sample is obtained without a tourniquet, or the tourniquet is released after the needle has entered the vein
- Handle sample gently to prevent hemolysis
- Maintain sample at room temperature
- Send to the lab within 45 minutes
- This test measures the serum concentration of potassium
- Potassium is the principal electrolyte (cation) of intracellular fluid
- Found mainly in the intracellular fluid (90%), and the remaining is distributed in the bones and the blood
- Potassium excretion:
- Primarily excreted by kidneys (80-90%)
- Sweat and stool (10-20%)
- When dietary potassium is nil, 40–50 mEq is still excreted daily in the urine
- Potassium is essential for various body processes such as:
- Nerve conduction
- Muscle function
- As primary intracellular inorganic buffer
- In enzyme reactions that transform glucose into energy and amino acids into proteins
- Maintenance of acid-base equilibrium
- To maintain osmotic pressure
- Along with calcium and magnesium, it controls the rate and force of contraction of the heart and, thus, cardiac output
- Affected by the adrenal hormones (esp. aldosterone)
- The clinical utility of the serum potassium test includes:
- To detect hypo or hyperkalemia (low or high potassium)
- To evaluate and monitor renal function, acid-base balance, and glucose metabolism
- To evaluate of electrolyte imbalances in:
- Acidotic or alkalotic states
- Elderly patients
- Patients on medications known to affect potassium
- Patients on hyperalimentation or dialysis
- Trauma
- Burns
- As part of evaluation of cardiac arrhythmias
- For routine screening of electrolytes in acute and chronic illness
- To evaluate neuromuscular and endocrine disorders
- To evaluate clinical signs of hyperkalemia or hypokalemia
- Screening in hypertensive patients
- Evaluate the response and efficacy of treatment for abnormal potassium levels
- Potassium has a significant and inverse relationship to pH: A decrease in pH of 0.1 increases the potassium level by 0.6 mEq/L
- Dietary intake of at least 40 mEq/day is essential
Additional information
- Normal day to day variation is 1-2%
- Variation of potassium levels within a given day can be as much as 20%, with a peak at 8.00 AM and decreasing during the day
- Related laboratory tests include:
- Aldosterone
- Anion gap
- Antiarrhythmic drugs
- Arterial blood gas
- Bicarbonate
- Blood gases
- Calcium
- Chloride
- Creatine kinase
- Electrolytes
- Osmolality
- Potassium (Urine)
- pH of blood
- Potassium, urine
- Serum creatinine
- Sodium (blood and urine)
Hyperkalemia (High potassium) EKG Findings:
- EKG findings suggestive of hyperkalemia include:
- Peaked T waves
- 2nd or 3rd degree AV block
- Loss of P waves or sine waves
- Changes are typically related to severity of the hyperkalemia
- As hyperkalemia worsens, the pattern is that of QRS widening with merging of the QRS and T waves, with the "sine wave" of hyperkalemia
- 5.5-6.5 mEq/L à Tall, peaked T-waves, shortened QT interval, ST segments can disappear
- >7 mEq/L à Decreased P wave amplitude, wide P-waves
- >8 mEq/L à Absent P-waves (e.g. sinus arrest), A-V block, QRS widening, ventricular tachycardia, ventricular fibrillation or "cardiac standstill"
Hypokalemia (Low potassium) EKG Findings:
- EKG findings suggestive of hypokalemia include:
- Flat T-wave
- ST depression
- Prominent U-waves
- Prolonged QT
- QRS complexes may widen when potassium drops below 3 mEq/L
- With progression of hypokalemia, these U waves reach "giant" size and fuse with the T waves as the potassium level drops to 1 mEq/L
- Severe hypokalemia or hypokalemia with concurrent digoxin use; Ventricular tachycardia or fibrillation may occur
Consult your laboratory for their normal ranges as these may vary somewhat from the ones listed below.
| Conv. units (mEq/L) | SI units (mmol/L) | |
|---|---|---|
| Adults | 3.5–5.2 | 3.5–5.2 |
| Children 1-17 years | 3.3–4.7 | 3.3–4.7 |
| Infants <1 year | 3.3–6.0 | 3.3-6.0 |
Neonates  7 days | 3.6–6.0 | 3.6–6.0 |
| Critcal Values | <2.5 | <2.5 |
| >7.0 | >7.0 |
Conditions associated with hyperkalemia include:
- Redistribution
- Metabolic or respiratory acidosis
- Diabetic ketoacidosis
- Diabetes without adequate insulin
- Hyperkalemic periodic paralysis
- Renal failure - acute or chronic with oliguria
- Urinary obstruction
- Addison's disease (Hypoaldosteronism)
- Adrenal insufficiency: e.g., patient on long term corticosteroids and sudden discontinuance
- Adrenogenital Syndrome: 21-Hydroxylase deficiency
- Cell damage as in
- Burns
- Chemotherapy
- Crush injuries
- Disseminated intravascular coagulation (DIC)
- Rhabdomyolysis
- Surgery
- Trauma
- Tumor lysis
- Dehydration
- High dietary intake
- Primary acquired hyperkalemia
- Interstitial nephritis
- Multiple myeloma
- Sickle cell disease
- SLE
- Tubular disorders
- Potassium Load
- Blood transfusions of aged blood
- IV Therapy, especially with K+ Supplements
- Massive muscle necrosis
- Patients with renal disease
- Pseudohypoaldosteronism
- Pseudohyperkalemia
- Ischemic blood draw (prolonged tourniquet use)
- Hemolysis
- Thrombocytosis (platelets > 1 million/mm3)
- Leukocytosis (WBC's > 70,000/mm3)
- Laboratory error
- Repeated fist clenching during venipuncture
- Delayed separation of serum from cells
- Familial pseudohyperkalemia, a rare disorder of RBC cation transport, leading to an increased rate of release of K+ from red cells at low temperatures
- Lipemic sample
- Drugs and substances
- Angiotensin converting enzyme (ACE) inhibitors
- Amiloride
- Aminocaproic acid
- Aminoglutethimide
- Ammonium chloride
- Antineoplastic agents
- Arginine infusion
- Atenolol
- Azithromycin
- Basiliximab
- Benazepril
- Beta adrenergic blockers
- Bisoprolol
- Cannabis
- Captopril
- Cefdinir
- Cefotaxime
- Clofibrate
- Cyclosporine
- Danazol
- Digoxin
- Enalapril
- Epoetin alfa
- Erythropoietin
- Etretinate
- Felodipine
- Fosphenytoin
- Fluoride
- Histamine
- Indomethacin
- Isoniazid
- Ketoconazole
- Ketorolac
- Labetalol
- Lisinopril
- Lithium
- Low molecular weight (LMW) heparin
- Lovastatin
- Mannitol
- Methicillin
- Methyltestosterone
- Metoprolol
- Micardis
- Mycophenolate
- Naproxen
- Netilmicin
- Nifedipine
- Norfloxacin
- NSAIDS
- Ofloxacin
- Paroxetine
- Penicillin G (high dose)
- Pentamidine
- Perindopril
- Pindolol
- Piroxicam
- Potassium supplements
- Potassium penicillin
- Potassium-sparing diuretics
- Propranolol
- Quinapril
- Quinupristin/dalfopristin
- Ramipril
- Risedronate
- Salt substitutes
- Sirolimus
- Somatotropin
- Spironolactone
- Succinylcholine
- Sulindac
- Tacrolimus
- THC
- Timolol
- Trandolapril
- Triamterene
- Trimethoprim
- Valsartan
- Venlafaxine
- Zalcitabine
Conditions associated with hypokalemia include:
- Most common cause in clinical practice is diuretic use causing hypokalemia
- Acute mountain sickness
- High dietary intake of sodium
- Intake of large amounts of licorice or chewing tobacco
- Urinary loss
- High aldosterone
- Adrenal tumor
- Bilateral adrenal hyperplasia
- Conn syndrome
- Malignant hypertension
- Renal artery stenosis
- Renin-producing tumor
- Low or absent aldosterone
- 11
-hydroxysteroid dehydrogenase inhibition - 11 -hydroxysteroid dehydrogenase deficiency
- Congenital adrenal hyperplasia
- Cushing's syndrome-pituitary or adrenal
- Ectopic corticotropin syndrome
- Liddle's syndrome
- Polyuria
- Renal tubular damage
- Chronic interstitial nephritis
- Chronic pyelonephritis
- Nephrotoxins
- Increased sodium delivery to distal nephron
- Distal Renal Tubular Acidosis (RTA) type I
- Diuretic therapy
- Hypercalcemic states
- Proximal tubulopathy (proximal [type II] RTA)
- Nonreabsorbable anion
- Bicarbonate:
- Vomiting
- Suction
- Alkali therapy for RTA
- Ketones
- Primary tubular disorders
- Bartter's syndrome
- Gitelman's syndromes
- Magnesium depletion
- Dietary
- Drugs (given below)
- Gastrointestinal
- Anorexia nervosa
- Cancer therapy
- Chemotherapy
- Radiation enteropathy
- Cirrhosis of liver
- Diarrhea of any cause
- Enteric fistula
- Geophagia/Clay ingestion
- Inadequate dietary intake
- Intestinal ion-transport defects as in congenital chloride diarrhea
- Jejuno-ileal bypass
- Laxative abuse
- Malabsorption
- Nasogastric tube suctioning
- Tumors
- Villous adenoma of the colon
- Zollinger-Ellison syndrome
- Vomiting
- Redistribution into the intracellular space
- Alkalosis (metabolic or respiratory)
- Barium intoxication
- Delirium tremens
- Diabetic ketoacidosis (especially with correction of acidosis)
- Familial hypokalemic periodic paralysis
- Hyperthyroidism
- Severe pernicious anemia - after treatment with B12 and folic acid
- Transfusion of frozen deglycerolized RBC
- Treatment of acidosis
- Other conditions
- Chronic alcoholism
- Cystic fibrosis
- Draining wounds
- Hypothermia
- Osmotic hyperglycemia
- Severe burns
- Sweating
- Drugs
- Acetazolamide
- Acetylsalicylic acid
- Alanine
- Albuterol
- Aldesleukin
- Aldosterone
- Aminoglycosides
- Amlodipine
- Amphetamines
- Amphotericin B
- Arsenic trioxide
- Aspirin
- Azathioprine
- Barium
- Benzthiazide
- Betamethasone
- Betaxolol
- Bicarbonate
- Bisacodyl
- Bronchodilators
- Bumetanide
- Caffeine
- Candesartan
- Capreomycin
- Carbamazepine
- Carbenicillin
- Carbenoxolone
- Carvedilol
- Cathartics
- Cephalexin
- Chewing Tobacco
- Chloroquine
- Chlorothiazide
- Cidofovir
- Cisplatin
- Clorexolone
- Corticosteroids
- Corticotropin
- Cortisone
- Decongestants
- Desoxycorticosterone
- Dexamethasone
- Diuretics
- Dobutamine
- Donepezil
- Doxazosin
- Doxorubicin
- Epinephrine
- Epoprostenol
- Ethacrynic acid
- Fluconazole
- Flucytosine
- Fludrocortisone
- Fluvoxamine
- Foscarnet
- Fosinopril
- Furosemide
- Gentamicin
- Glucocorticoids
- Glucose
- Gossypol
- Hydrochlorothiazide
- Hydrocortisone
- Hydroflumethiazide
- Imatinib
- Indapamide
- Insulin
- Itraconazole
- Ketoprofen
- Kayexylate
- Laxatives
- Levodopa
- Licorice
- Lomefloxacin
- Methazolamide
- Methyclothiazide
- Methylprednisolone
- Metoclopramide
- Metolazone
- Milrinone
- Mineralocorticoids
- Mithramycin
- Moxalactam
- Nabumetone
- Neomycin
- Nisoldipine
- Ondansetron
- Pamidronate
- Pergolide
- Phenolphthalein
- Phosphates
- Piperacillin
- Plicamycin
- Polystyrene sulfonate
- Polythiazide
- Prednisolone
- Prednisone
- Quinethazone
- Riluzole
- Risperidone
- Ritodrine
- Sodium bicarbonate
- Sodium Polystyrene Sulfonate
- Sorbitol
- Streptozocin
- Terbutaline
- Tetracycline
- Theophylline
- Thiazides
- Ticarcillin
- Tobramycin
- Toluene
- Trichlormethiazide
- Verapamil
- Vidarabine
- Xanthines
Causes of pseudohypokalemia or false negative values of potassium include:
- In blood drawn into a heparinized tube, if there is a delay in separation of samples at warm ambient temperatures, there is often continued uptake of K+ into cells
- Advani A et al. Life-threatening hypokalaemia on a low-carbohydrate diet associated with previously undiagnosed primary hyperaldosteronism [corrected]. Diabet Med. 2005 Nov;22(11):1605-7.
- Andrioli M et al. Isolated corticotrophin deficiency. Pituitary. 2006 Oct 30; [Epub ahead of print].
- Dursun I et al. Difficulties in maintaining potassium homeostasis in patients with heart failure. Clin Cardiol. 2006 Sep;29(9):388-92.
- Haris A et al. [Transtubular potassium gradient in the diagnosis of potassium metabolism disorders] [Article in Hungarian]. Orv Hetil. 2000 Feb 20;141(8):385-91.
- Hollander-Rodriguez JC et al. Hyperkalemia. Am Fam Physician. 2006 Jan 15;73(2):283-90.
- Laboratory Corporation of America. Potassium, Serum. [Homepage on the internet]©2003. Last updated on November 2, 2006. Last accessed on November 6, 2006. Available at URL: http://www.labcorp.com/datasets/labcorp/html/chapter/mono/pr007300.htm
- LabTestsOnline®. Potassium. [Homepage on the Internet] ©2001-2006. Last reviewed onApril 13, 2005. Last accessed on November 6, 2006. Available at URL: http://www.labtestsonline.org/understanding/analytes/potassium/sample.html
- Mann JF et al. Serum potassium, cardiovascular risk, and effects of an ACE inhibitor: results of the HOPE study. Clin Nephrol. 2005 Mar;63(3):181-7.
- Shaer AJ et al. Inherited primary renal tubular hypokalemic alkalosis: a review of Gitelman and Bartter syndromes. Am J Med Sci. 2001 Dec;322(6):316-32.
- UTMB Laboratory Survival Guide®. POTASSIUM, serum. [Homepage on the Internet]© 2006. Last reviewed in February 2006. Last accessed on November 21, 2006. Available at URL: http://www.utmb.edu/lsg/LabSurvivalGuide/chem/POTASSIUMserum.html