Serum Potassium

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Latest Edit: Hector 2014-3-28 (EDT)

See Also Lab Tests

Potassium is the main cation found in the intracellular fluid and acts as the primary intracellular pH buffer. It is mainly found inside the cell (90%), while small amounts found in other tissues such as bone and blood. Potassium excretion occurs largely by the kidney (80-90%) via the urine, and the remainder is excreted in the sweat and stool. Since the kidney does not conserve potassium and will continue to excrete it, if adequate amounts of potassium are not consumed on a daily basis, a potassium deficiency can occur. [1],[2]

Contents

Discussion

  • Potassium and sodium together play an important role in the kidney's regulation of pH, potassium bicarbonate being the major intracellular inorganic buffer. Potassium excretion is largely controlled by the kidney. The kidney does not conserve potassium, therefore a potassium deficiency can occur if inadequate amounts of potassium are consumed daily.
  • Nerve conduction
  • Maintenance of osmotic pressure
  • Muscle function
  • Cellular transport via the sodium-potassium pump
  • Acid-base balance
  • Controlling the rate of force of cardiac muscle contraction, and thus controlling cardiac output, along with calcium and magnesium.
  • Kidney regulation of pH, along with sodium
  • Potassium levels will increase with cellular damage, which causes the potassium to leach into the extracellular fluid.
  • Common indications of potassium need:

Patient Preparation

  • No special diet or fasting is required.
  • Factors which can cause increased levels
  • Hemolyzed blood, excessive intake of herbal Licorice
  • Drugs: aminocaproic acid, antibiotics, antineoplastic drugs, captopril, epinephrine, heparin, histamine, isoniazid (INH), lithium, mannitol, K-sparing diuretics, K supplements, and succinylcholine.
  • Factors which can cause decreased levels
  • Glucose administered during tolerance testing, ingestion and administration of large amounts of glucose in patients with heart disease.
  • Drugs: acetazolamide, aminosalicylic acid, glucose infusions, amphotericin B, carbenicillin, cisplatin, diuretics (K wasting), insulin, laxatives, lithium carbonate, penicillin G sodium (high doses), phenothiazines, salicylates (aspirin), and sodium polystyrene sulfonate (kayexalate)

Clinical Implications

Ranges: The following are the reference ranges for this lab. However, lab ranges can vary by laboratory and country. [2]

Standard U.S. Units Standard International Units
Conventional Laboratory Range 3.5-5.3 mEq/L 3.5-5.3 mmol/L
Optimal Range 4.0-4.5 mEq/L 4.0-4.5 mmol/L
Alarm Ranges <3.0 or >6.0 mEq/L <3.0 or >6.0 mmol/L

High levels indicate:

Low levels indicate:

Associated Tests

References

  1. Pagana Kathleen D, Pagana Timothy J, (1998) Mosby's Manual of Diagnostic and Laboratory Tests, Mosby, Inc
  2. 2.0 2.1 Weatherby Dicken, Ferguson Scott (2002) Blood Chemistry and CBC Analysis: Clinical Laboratory Testing from a Functional Perspective, Bear Mountain
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