Specimen Information

Type

Stool

Volume

5.0 g

Transport Info

Refrigerated

Fasting Required?

False

Clinical Significance

The excessive ingestion of magnesium causes diarrhea. Because magnesium acts as an osmotic cathartic agent, magnesium-induced diarrhea is associated with a high fecal output of magnesium. The upper limits of normal for the fecal output of magnesium is 35 mg/day and for the fecal magnesium concentration, 110 mg/ dL. These levels were established in normal subjects, both when they had normally formed stools and when diarrhea was induced by mechanisms other than increased magnesium ingestion.The fecal output of soluble magnesium that exceeds 35 mg/day or a fecal magnesium concentration that exceeds 110 mg/dL, or both, suggests that magnesium has a major role in the pathogenesis of diarrhea.In the context of a high magnesium output, a fecal magnesium concentration above 240 mg/dL suggests that magnesium is the only cause of the diarrhea. When magnesium output is high, but the fecal concentration is less than 240 mg/ dL, magnesium is not the only cause of the diarrhea.