Sorted By Test Name - Mayo Medical Laboratories

KBF
8028
KF
8375
Potassium, Body Fluid
Clinical Information: Potassium (K(+)) is the major cation of the intracellular fluid. Disturbance of
potassium homeostasis has serious consequences. Decrease in extracellular potassium is characterized by
muscle weakness, irritability, paralysis, fast heart rate, specific cardiac conduction effects that are
apparent by electrocardiographic examination, and eventual cardiac arrest. More than 90% of
hypertensive patients with aldosteronism have a hypokalemia (low K(+)). Low K(+) also is common in
vomiting, diarrhea, alcoholism, and folic acid deficiency. Abnormally high extracellular K+ levels
produce symptoms of mental confusion; weakness, numbness and tingling of the extremities; weakness of
the respiratory muscles; flaccid paralysis of the extremities; slowed heart rate, and eventually peripheral
vascular collapse and cardiac arrest. Hyperkalemia may be seen in end stage renal failure, hemolysis,
trauma, Addison's disease, metabolic acidosis, acute starvation, dehydration, and with rapid K(+) infusion.
Useful For: Measurement of serum potassium is used for evaluation of electrolyte balance, cardiac
arrhythmia, muscular weakness, hepatic encephalopathy, and renal failure. Potassium should be
monitored during treatment of many conditions but especially in ketoacidosis of diabetes mellitus and any
intravenous therapy for fluid replacement.
Interpretation: Plasma K=values less than 3.0 mEq/L are associated with marked neuromuscular
symptoms and are evidence of a critical degree of intracellular depletion. K(+) values < 2.5 mEq/L are
potentially life-threatening.
Reference Values:
Not applicable
Potassium, Random, Feces
Clinical Information: Potassium is an intracellular cation normally present in fecal water at a
concentration approximately 20 times higher than the serum concentration. The fecal water potassium
content is comprised of 2 fractions-approximately 15% of the normal dietary intake of potassium (80
mEq/day) passes through the gastrointestinal (GI) tract to be deposited directly in fecal water, and a small
fraction of potassium crosses the epithelial barrier of the GI tract from extra cellular fluids based on
osmotic pressure. In adults, the median daily excretion of potassium is 9 mEq/day, ranging from 0
mEq/day to 30 mEq/day. The median concentration of potassium in fecal water is 40 mEq/kg, ranging
from 0 mEq/day to 200 mEq/kg. Potassium excretion is race-related; excretion in blacks is less than in
Caucasians, usually by a factor of 2. The fecal water potassium concentration and daily excretion rate will
be normal if the cause of diarrhea is bacteria or due to ingestion of osmotic agents such as magnesium,
phenolphthalein, and sulfate. The fecal water potassium daily excretion rate will be normal, but the
measured concentration will be increased in patients with contracted colon volume. Both the daily
excretion rate of potassium and potassium concentration will be elevated in ulcerative colitis or other
diseases where there is bleeding into the GI tract, exposure to cholera toxin, and in patients with islet cell
tumors, increased secretion of vasointestinal peptide (vipoma syndrome), primary aldosteronism,
ingestion of mineralocorticoids, and due to bacterial metabolism of unabsorbed carbohydrates passing
through the GI tract.
Useful For: Work-up of a patient with chronic diarrhea
Interpretation: Typically, stool potassium is 20 times serum potassium. A useful formula is 2x (stool
sodium + stool potassium) = stool osmolality + or - 30 mOsm. Fecal potassium concentration and daily
excretion rate are usually below the median level in patients with osmotic diarrhea. Normal fecal sodium
and potassium in the presence of an osmotic gap (>30 mOsm/kg) suggests osmotic diarrhea. Increased
fecal sodium content or daily excretion rate with normal fecal potassium and no osmotic gap indicates
secretory diarrhea. High fecal potassium in association with normal or low fecal sodium suggests
deterioration of the epithelial membrane or a bleeding lesion. High sodium and potassium (3 times
normal) in the absence of an osmotic gap indicate active electrolyte transport in the gastrointestinal (GI)
tract that might be induced by agents such as cholera toxin, hypersecretion of vasointestinal peptide, or
islet cell tumor. For very low stool osmolality, consider factitial diarrhea. The fecal potassium
concentration and excretion rate are increased 2-fold to 3-fold with ulcerative colitis, or bleeding into the
GI tract, when exposed to cholera toxin, with ingestion of mineralocorticoids, in primary aldosteronism,
Current as of January 4, 2013 7:15 pm CST 800-533-1710 or 507-266-5700 or MayoMedicalLaboratories.com Page 1458