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Stool osmotic gap is a calculation performed to distinguish among different causes of diarrhea. It is calculated with the equation 290 − 2 * (stool Na + stool K).〔(【引用サイトリンク】title=Diarrhea: Approach to the Patient With Lower GI Complaints: Merck Manual Professional )〕 The 290 is the value of the plasma osmolality. The stool osmolality is usually not directly measured, and is often given a constant in the range of 290 to 300. A low stool osmolic gap can imply secretory diarrhea, while a high gap can imply osmotic diarrhea. The reason for this is that secreted sodium and potassium ions make up a greater percentage of the stool osmolality in secretory diarrhea, whereas in osmotic diarrhea, molecules such as unabsorbed carbohydrates are more significant contributors to stool osmolality. A normal gap is between 50 and 100 mosm/kg. High osmotic gap (>100 mosm/kg) causes of osmotic diarrhea include celiac sprue, chronic pancreatitis, lactase deficiency, lactulose, laxative use/abuse, and Whipple's disease. Low osmotic gap (<50 mosm/kg) causes of secretory diarrhea include toxin-mediated causes (cholera, enterotoxigenic strains of ''E. coli'') and secretagogues such as vasoactive intestinal peptide (from a VIPoma, for example). Uncommon causes include gastrinoma, medullary thyroid carcinoma (which produces excess calcitonin), factitious diarrhea from laxative abuse and villous adenoma. ==References== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Stool osmotic gap」の詳細全文を読む スポンサード リンク
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