Mayo Test Catalog, (Sorted By Test Name) - Mayo Medical ...

ELPN
87972
EFP24
60035
Clinical References: Homburger HA: Allergic diseases. In Clinical Diagnosis and Management
by Laboratory Methods. 21st edition. Edited by RA McPherson, MR Pincus. New York, WB Saunders
Company, 2007, Chapter 53, Part VI, pp 961-971
Electrolyte Panel, Serum
Clinical Information: See Individual Unit Codes
Useful For: See Individual Unit Codes
Interpretation: See Individual Unit Codes
Reference Values:
See individual test listings.
Clinical References: See Individual Unit Codes
Electrolytes, 24 Hour, Feces
Clinical Information: The concentration of electrolytes in fecal water and their rate of excretion
are dependent upon 3 factors: -The normal daily dietary intake of electrolytes. -Electrolytes are
passively transported from serum and other vascular spaces to equilibrate fecal osmotic pressure with
vascular osmotic pressure -Exogenous substance and rare toxins (cholera toxin) cause electrolyte
transport into fecal water Fecal osmolality is normally in equilibrium with vascular osmolality, and
sodium is the major affector of this equilibrium. Fecal osmolality is normally 2 x (sodium + potassium)
unless there are exogenous factors inducing a change in this ratio, such as the presence of other osmotic
agents (magnesium sulfate, saccharides), or drugs inducing secretions, such as phenolphthalein or
bisacodyl.
Useful For: The work-up of cases of chronic diarrhea Making the diagnosis of factitial diarrhea The
relationship, osmolality equals 2 x (sodium + potassium), is the basis for this evaluation.
Interpretation: A useful formula is 2x (stool sodium + stool potassium)=stool osmolality + or - 30
mOsm. Typically, stool osmolality is similar to serum since the gastrointestinal (GI) tract does not
secrete water. Osmotic Diarrhea: If the measured osmolality exceeds the calculation of 2 x (sodium +
potassium) by >30 mEq/kg, an osmotic gap exists indicating osmotic diarrhea. Fecal potassium
concentration and daily excretion rate are usually below the median level in patients with osmotic
diarrhea. Modest increases (2x) in fecal chloride concentration and excretion rate may be observed
when fecal sodium is elevated in association with osmotic diarrhea. Osmotic agents such as magnesium,
sorbitol, or polyethylene glycol may be the cause of this. Magnesium concentration of >200 mEq/kg is
frequently associated with decreased fecal sodium and potassium and is an indicator of excessive
consumption of magnesium, a common cause of osmotic diarrhea. Secretory Diarrhea: Increased fecal
sodium and chloride content or daily excretion rate with normal fecal potassium and no osmotic gap
indicates secretory diarrhea. If sodium concentration or 24-hour sodium excretion rate is 2 to 3 times
normal and osmotic gap >30 mOsm/kg, secretory diarrhea is also indicated. Agents such as
phenolphthalein, bisacodyl, or cholera toxin should be suspected. An osmotic gap >100 mOsm/kg
indicates factitial diarrhea, likely due to magnesium or phenolphthalein consumption. For very low stool
osmolality, consider factitial diarrhea. Normal or low fecal sodium in association with high fecal
potassium suggests deterioration of the epithelial membrane or a bleeding lesion High sodium and
potassium in the absence of an osmotic gap indicate active electrolyte transport in the GI tract that
might be induced by agents such as cholera toxin or hypersecretion of vasointestinal peptide. Fecal
chloride concentration or daily excretion rate are markedly elevated (7-10 times normal) in association
with congenital hypochloremic alkalosis with chloridorrhea.
Reference Values:
CHLORIDE
0-15 years: not established
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