Dec 7, 2010

Potassium (K+) test

          About 90% of potassium is concentrated within the cells and the remainder is contained in blood and bone. Plasma potassium influences nerve conduction, muscle activity, and, most important, cardiac function. Minimal changes in plasma potassium levels can have profound and adverse affects on heart muscle. Since the kidneys do not reabsorb or conserve potassium, adequate dietary intake is necessary to prevent potassium deficiency.

Normal Range

Adult            3.5-5.0 mEq/L
Children       3.4-4.7 mEq/L
Infant          4.1-5.3 mEq/L

      Variations from Normal. An increase in plasma potassium levels, hyperkalemia, is usually attributed to renal failure . Other common causes of hyperkalemia include acidosis, Addison's disease, internal hemorrhage, and massive tissue or cellular damage. Since 90% of potassium is contained within the cells, cell damage as in cases of burns, chemotherapy, and disseminated intravascular coagulation (DIC) results in the release of potassium into the blood.
Hypokalemia, a decrease in plasma potassium, is most often associated with loss of fluid from the gastrointestinal tract.

      Therefore, any disease process that causes diarrhea or severe vomiting has the potential for creating potassium deficiency. Other disorders associated with hypokalemia include malabsorption syndromes, hyperaldosteronism (increased secretion of aldosterone), Cushing's syndrome, and renal tubular acidosis.

       Hypokalemia can cause serious cardiac problems such as premature ventricular contraction, paroxysmal atrial tachycardia, ventricular tachycardia, and ventricular fibrillation. Plasma potassium levels of 2.5 mEq/L or less, or 6 .5 mEq/L or more can cause heart problems that lead to death.

Interfering Circumstances. Venipuncture, intravenous fluid administration, and certain medications can alter plasma potassium levels. The common practice of opening and closing the fist with a tourniquet in place prior to venipuncture may increase potassium levels. Intravenous fluid administration without adequate potassium supplements can lead to potassium depletion. Medications that may cause an increased potassium level include heparin, histamine, mannitol, and lithium. Drugs that may cause a decreased level are insulin, aspirin, cisplatin, and potassium wasting diuretics.

       Dietary habits do not usually interfere with plasma potassium levels. A relatively well-balanced diet will provide an adequate supply of potassium. However, excessive licorice ingestion can cause a decrease in plasma potassium levels.

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