If the levels of potassium within the body are low, then the condition called hypokalemia occurs. According to "Harrison's Principles of Internal Medicine," potassium is the major positively charged ion in the internal cellular environment that is called the intracellular fluid, or ICF. Movement of potassium in and out of the cell is crucial for electrophysiology of the cellular membrane that is known as the resting membrane potential. The conduction of ionic charges across the membrane carried by potassium plays an essential role in neuromuscular function.
Low Plasma Levels
Normal plasma potassium values range from 3.5 to 5.0 millimoles per liter blood volume, or mmol/L, with the values being higher for newborns at 3.7 to 5.9 mmol/L, according to "The John's Hopkins Hospital: The Harriet Lane Handbook."
Hypokalemia occurs at blood levels lower than 3.5 mmol/L in adults and 3.7 mmol/L in infants. Severe hypokalemia of less than 3.0 mmol/L can result in dangerous arrhythmias and muscular paralysis, according to "2007 Current Consult Medicine." Potassium is forced out of the extracellular fluid or ECF and into the ICF, thus effectively reducing the amount of the ion present in the blood.
Low Urine levels
Renal excretion is the most important method of potassium regulation. The kidneys conduct more than 80 percent of potassium elimination from the body, according to "Step-Up to Medicine" authored by Drs. Steven Agabegi and Elizabeth Agabegi, with the remainder excreted in the stool.
Normal urine levels vary between 25 and 120 milliequivalents per liter of volume per day, or mEq/L/d. "The Johns Hopkins Hospital: The Harriet Lane Handbook" states that urine potassium can increase in conditions of hypokalemia, caused by problems in the renin-angiotensin-aldosterone system, such as Cushing's syndrome and excess renin. Other hypokalemic abnormalities can present with decreased urine potassium <20 mEq/L/d, which include diarrhea, laxative abuse and malnutrition.
Low Stool Levels
The gastrointestinal system effectively absorbs approximately 90 percent of the potassium within the diet and excretes nearly 10 to 20 percent, according to "Step-Up to Medicine." "Harrison's Principles of Internal Medicine" states that normal amounts of potassium in stool are between 5 and 10 mmol/d per 200 ml of fecal matter. The most common relationship between gastrointestinal loss of potassium and hypokalemia is through diarrhea. Large-volume diarrhea can result in a severe depletion of potassium. When levels decrease below 5 mmol/d/ 200 ml, then the patient could have renal tubular acidosis, Bartter syndrome or Fanconi syndrome.
References
- "Harrison's Principles of Internal Medicine" 17th ed.; Anthony Fauci, M.D., et al., eds.; 2008
- "2007 Current Consult Medicine"; Maxine Papadakis, M.D., and Stephen McPhee, M.D.; 2007
- "The Johns Hopkins Hospital: The Harriet Lane Handbook" 17th ed.; Jason Roberston, M.D., and Nicole Shilkofski, M.D.; 2005
- "Step-Up to Medicine" 2nd ed.; Steven Agabegi, M.D., and Elizabeth Agabegi, M.D.; 2008
- "BRS: Physiology" 4th ed.; Linda Costanzo, Ph.D.; 2007
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