Khouri M R, Huang G, Shiau Y F
Department of Medicine, Veterans Administration Medical Center, Philadelphia, Pennsylvania.
Gastroenterology. 1989 Feb;96(2 Pt 1):421-7. doi: 10.1016/0016-5085(89)91566-7.
The 72-h fecal fat determination is used as the gold standard to document the presence of steatorrhea. Although the Sudan stain for fecal fat is advocated as a sensitive screening test, a quantitative correlation between the 72-h fecal fat quantitation and the fecal Sudan stain is lacking. This study was designed to examine the staining properties of different classes of purified lipids in an experimentally defined artificial matrix, and to elucidate the reasons for the lack of quantitative correlation between these two tests. Our results indicate that the "neutral fat" stain without acidification or heating identifies triglyceride; and at an appropriate pH, the "neutral stain" also identifies fatty acid. The "split fat" stain with acidification and heating identifies both triglyceride and fatty acid. After acidification, fatty acid soaps are converted to the nonionized fatty acid. Thus, fatty acid soaps can be identified indirectly as fat droplets that are stained by the split fat stain. Although cholesterol is stained with Sudan stain after heating, upon cooling, cholesterol forms crystals of anhydrous cholesterol, making its staining pattern distinct. Neither the neutral fat nor the split fat stain can detect phospholipid or cholesteryl ester. The 72-h fecal fat determination is a measure of the total fatty acid content after a specimen is saponified. The resulting fatty acids are derived from a variety of endogenous and exogenous sources, including free fatty acids, soaps of fatty acids, triglycerides, cholesterol esters, and phospholipids. Therefore, the 72-h fecal fat quantitation does not differentiate between the primary sources of the measured fatty acid. It is concluded that the 72-h fecal fat determination is not specific for documenting triglyceride (fat) malabsorption. Until new methods are developed that specifically measure fecal triglyceride and fatty acid, the Sudan stain of fecal fat appears to be a more specific method for detecting the presence of triglyceride and fatty acid in a matrix.
72小时粪便脂肪测定被用作记录脂肪泻存在的金标准。尽管粪便脂肪苏丹染色被提倡作为一种敏感的筛查试验，但72小时粪便脂肪定量与粪便苏丹染色之间缺乏定量相关性。本研究旨在研究不同类别的纯化脂质在实验确定的人工基质中的染色特性，并阐明这两种试验缺乏定量相关性的原因。我们的结果表明，未经酸化或加热的“中性脂肪”染色可识别甘油三酯；在适当的pH值下，“中性染色”也可识别脂肪酸。经酸化和加热的“分解脂肪”染色可识别甘油三酯和脂肪酸。酸化后，脂肪酸皂转化为非离子化脂肪酸。因此，脂肪酸皂可间接识别为被分解脂肪染色的脂肪滴。尽管胆固醇在加热后用苏丹染色，但冷却后，胆固醇会形成无水胆固醇晶体，使其染色模式不同。中性脂肪染色和分解脂肪染色均无法检测磷脂或胆固醇酯。72小时粪便脂肪测定是对标本皂化后总脂肪酸含量的一种测量。产生的脂肪酸来自多种内源性和外源性来源，包括游离脂肪酸、脂肪酸皂、甘油三酯、胆固醇酯和磷脂。因此，72小时粪便脂肪定量无法区分所测脂肪酸的主要来源。得出的结论是，72小时粪便脂肪测定并非专门用于记录甘油三酯（脂肪）吸收不良。在开发出专门测量粪便甘油三酯和脂肪酸的新方法之前，粪便脂肪苏丹染色似乎是检测基质中甘油三酯和脂肪酸存在的更特异方法。
