Duncan A, Robertson C, Russell R I
Gastroenterology Unit, Royal Infirmary, Glasgow, Scotland.
J Lab Clin Med. 1992 Apr;119(4):359-63.
The fecal osmotic gap is considered to be useful in the investigation of chronic diarrhea. However, two important questions regarding the calculation of the osmotic gap remain unanswered: the effect of the method of measuring osmolality and the most appropriate means for its calculation. In 41 patients with varying causes of diarrhea, stool osmolalities and electrolyte concentrations were measured. Measurement of stool osmolality by a dew point technique underestimated results by a variable factor, which makes it an inappropriate method. Fecal osmolality measured by freezing point depression gave reliable results and so was considered to be preferable. The osmotic gap was calculated by two methods: subtraction of the calculated osmolality from (1) stool osmolality and (2) plasma osmolality. The former approach was found to be inappropriate on the basis of large variations in results when consecutive stool samples were analyzed, a poor correlation with the severity of osmotic diarrhea, poor resolution between results from patients with secretory diarrhea and those with osmotic diarrhea, and practical difficulties in ensuring adequate collection of stool samples.
粪便渗透间隙被认为在慢性腹泻的调查中有用。然而，关于渗透间隙计算的两个重要问题仍未得到解答：测量渗透压的方法的影响以及最适合的计算方法。对41例不同病因的腹泻患者进行了粪便渗透压和电解质浓度的测量。用露点技术测量粪便渗透压会使结果低估一个可变因素，这使其成为一种不合适的方法。通过冰点降低法测量的粪便渗透压给出了可靠的结果，因此被认为是更可取的。渗透间隙通过两种方法计算：从（1）粪便渗透压和（2）血浆渗透压中减去计算出的渗透压。基于对连续粪便样本进行分析时结果的巨大差异、与渗透性腹泻严重程度的相关性较差、分泌性腹泻患者和渗透性腹泻患者结果之间的分辨率较差以及确保充分收集粪便样本的实际困难，发现前一种方法不合适。
