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Potassium (K)

Definition

  • Potassium is a primary intracellular ion; <2% is extracellular. High intracellular concentrations are maintained by the Na " “K ATPase pump, which continuously transports potassium into the cell against a concentration gradient. This pump is a critical factor in maintaining and adjusting the ionic gradients, on which nerve impulse transmission and contractility of cardiac and skeletal muscle depends. In acidemia, potassium moves out of cells; in alkalemia, potassium moves into cells. Hypokalemia inhibits aldosterone production; hyperkalemia stimulates aldosterone production. Plasma sodium and potassium control potassium reabsorption. Each 1 mmol/L decrease of serum potassium reflects a total deficit of <200 " “400 mmol; a serum potassium <2 mmol/L may reflect a total deficit >1,000 mmol.
  • Normal range: see Table 16.67.

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TABLE 16 " “67Normal Range for PotassiumView LargeTABLE 16 " “67Normal Range for Potassium From Age Reference Range (mmol/L) Critical Range (mmol/L) 0 " “4 mo 4.0 " “6.2 <2.6 >7.5 4 mo " “1 y 3.7 " “5.6 <2.6 >7.5 >1 y 3.5 " “5.3 <3.0 >6.2

Use

  • Evaluation of electrolyte balance, cardiac arrhythmia, muscular weakness, hepatic encephalopathy, and renal failure
  • Diagnosis and monitoring hyperkalemia and hypokalemia in various conditions (e.g., treatment of diabetic coma, renal failure, severe fluid and electrolyte loss, effect of certain drugs)
  • Diagnosis of familial hyperkalemic periodic paralysis and hypokalemic paralysis

Interpretation

Increased In

  • Potassium retention GFR <3 " “5 mL/minute Oliguria caused by any condition (e.g., renal failure) Chronic nonoliguric renal failure associated with dehydration, obstruction, trauma, or excess potassium Drugs Renal toxicity (e.g., amphotericin B, methicillin, tetracycline) GFR >20 mL/minute Decreased (aldosterone) mineralocorticoid activity Addison disease Hypofunction of the renin " “angiotensin " “aldosterone system Hyporeninemic hypoaldosteronism with renal insufficiency (GFR, 25 " “75 mL/minute) Various drugs (e.g., NSAIDs, ACE inhibitors, cyclosporine, pentamidine) Decreased aldosterone production Pseudohypoaldosteronism Aldosterone antagonist drugs (e.g., spironolactone, captopril, heparin) Inhibition of tubular secretion of potassium Drugs (e.g., spironolactone, triamterene, amiloride) Hyperkalemic type of distal RTA (e.g., sickle cell disease, obstructive uropathy) Mineralocorticoid-resistant syndromes Primary tubular disorders Hereditary Acquired (e.g., SLE, amyloidosis, sickle cell nephropathy, obstructive uropathy, renal allograft transplant, chloride shift)
  • Potassium redistribution Familial hyperkalemic periodic paralysis (Gamstorp disease, adynamia episodica hereditaria) Acute acidosis (especially hyperchloremic metabolic acidosis; less with respiratory; little with metabolic acidosis due to organic acids) (e.g., diabetic ketoacidosis, lactic acidosis, acute renal failure, acute respiratory acidosis) Decreased insulin Beta-adrenergic blockade Drugs (e.g., succinylcholine, great excess of Digitalis, arginine infusion) Use of hypertonic solutions (e.g., saline, mannitol) Intravascular hemolysis (e.g., transfusion reaction, hemolytic anemia), rhabdomyolysis Rapid cellular release (e.g., crush injury, chemotherapy for leukemia or lymphoma, burns, major surgery)
  • Urinary diversion Ureteral implants into jejunum In neonates " ”dehydration, hemolysis (e.g., cephalohematoma, intracranial hemorrhage, bruising, exchange transfusion), acute renal failure, CAH, adrenocortical insufficiency

Decreased In

  • Excess renal excretion (in patients with hypokalemia, urine potassium, >25 mmol in 24 hours or >15 mmol/L implies at least a renal component) Osmotic diuresis of hyperglycemia (e.g., uncontrolled diabetes) Nephropathies Renal tubular acidosis (proximal and especially distal) Bartter syndrome Liddle syndrome Magnesium depletion due to any cause Renal vascular disease, malignant hypertension, vasculitis Renin-secreting tumors Endocrine Hyperaldosteronism (primary, secondary) Cushing syndrome especially caused by ectopic ACTH production CAH Hyperthyroidism (especially in Asian persons) Drugs Diuretics (e.g., thiazides, ethacrynic acid, furosemide); assay for diuretics should be done if urine chloride >40 mmol/L Mineralocorticoids (e.g., fluorocortisone) High-dose glucocorticoids High-dose antibiotics (e.g., penicillin, nafcillin, ampicillin, carbenicillin) Substances with mineralocorticoid effect (e.g., glycyrrhizic acid [licorice], carbenoxolone, gossypol) Drugs associated with magnesium depletion (e.g., aminoglycosides, cisplatin, amphotericin B, foscarnet) Acute myelogenous, monomyeloblastic, or lymphoblastic leukemia
  • Nonrenal causes of excess potassium loss In patients with hypokalemia, urine potassium levels should be <25 mmol/24 hours. If levels drops to <15 mmol/L it implies extrarenal loss. GI Vomiting Diarrhea (e.g., infections, malabsorption, radiation) Drugs (e.g., laxatives [phenolphthalein], enemas, cancer therapy) Neoplasms (e.g., villous adenoma of the colon, pancreatic VIPoma that produces VIP >200 pg/mL, Zollinger-Ellison syndrome) Excessive spitting (sustained expectoration of all saliva in neurotic persons and to induce weight loss in professional wrestlers) Skin Excessive sweating CF Extensive burns Draining wounds Cellular shifts Respiratory alkalosis Classic periodic paralysis Insulin Drugs (e.g., bronchodilators, decongestants) Accidental ingestion of barium compounds Treatment of severe megaloblastic anemia with vitamin B12 or folic acid Physiologic (e.g., highly trained athletes) Diet Severe eating disorders (e.g., anorexia nervosa, bulimia) Dietary deficiency Delirium tremens In neonates " ”asphyxia, alkalosis, renal tubular acidosis, iatrogenic (glucose and insulin), diuretics
  • Major causes of hypokalemia with hypertension: Diuretic drugs (e.g., thiazides) Primary aldosteronism Secondary aldosteronism (renovascular disease, renin-producing tumors) Cushing syndrome Malignant hypertension Renal tubular acidosis

Limitations

  • Laboratory artifacts Hemolysis during venipuncture, conditions associated with thrombocytosis or leukocytosis, incomplete separation of serum and clot, double spinning (respinning) of blood collection tubes Arm in upward position while collecting blood Betadine application Laboratory order of draw (lavender top tubes drawn before serum chemistry tubes) Drawing above IV site Vigorously mixed tubes Collection techniques Traumatic draw Pneumatic tube system issues: speed too high, unpadded canisters, excessive agitation Delay in processing Centrifuging at too high G force Increased heat exposure in centrifuge Chilling whole blood beyond 2 hours Prolonged tourniquet use and hand exercise when drawing blood
  • Potassium value can be elevated approximately 15% in slight hemolysis (Hb ≤50 mg/dL) and elevated approximately 30 " “50% in moderate hemolysis (Hb >100 mg/dL). Therefore, potassium status can be assessed in those with slight hemolysis but not in those with moderate hemolysis.
  • Excess dietary intake or rapid potassium infusion.
  • Drugs with high potassium content (e.g., 1 million units of penicillin G potassium contains 1.7 mmol of potassium).
  • Transfusion of old blood.