Malabsorption syndrome is a syndrome caused by various causes of malabsorption of nutrients from the small intestine, which must undergo adequate digestion. The clinical manifestations of malabsorption syndrome, in addition to the symptoms and signs specific to the primary disease causing malabsorption, are mainly a series of pathophysiological changes caused by a variety of nutrient absorption disorders. Examination items: 1, fecal fat examination (1) Sudan III staining microscopy: normal fecal fat droplets do not appear, such as > 10 droplets / high magnification field, indicating abnormal fat absorption. (2) Faecal fat quantification: normal >6g/24 hours, can diagnose malabsorption syndrome. 2, fat balance test Daily intake of test meal containing more than 70g of fat for 6 days. The fat content was measured in the stool 72 hours after collection (day 4-6) and the absorption rate was calculated. Fat absorption rate = fat intake (after 3 days) – fecal fat (after 3 days) / (fat intake) × 100. Normal value: >95%, below normal indicates impaired fat absorption. 3, D-Xylose absorption test D-Xylose (D-Xylose) is a kind of pentose, after oral administration, it is not decomposed by digestive enzymes, absorbed directly through the jejunal mucosa, not metabolized in the body, and excreted from the kidney. If the renal function is normal, the measurement of urinary D-Xylose excretion can reflect the absorption function of small intestine. Method: Take 5g of D-xylose orally on an empty stomach, collect urine for 5 hours and measure the urinary D-xylose. Normal value: >1.25g (25%), 1.0~1.2g is suspicious, <1.0g (20%) is abnormal. 4, vitamin B12 absorption test Reflect ileal absorption function, first inject vitamin B12 1000ug, so that the body saturated, oral 60 cobalt labeled vitamin B122ug, collect 48 hours urine, determine the amount of 60 cobalt, normal value: > 8-10%, 2-7% for moderate malabsorption, < 2% severe malabsorption. Mostly used to check small intestinal bacterial overgrowth. 5, BT-PABA (also known as pancreatic function peptide) test Benzoyl-L tyrosine-para-aminobenzoic acid (BT-PABA) after oral administration, in the small intestine by chymotrypsin decomposition, free para-aminobenzoic acid is easily absorbed by the small intestine, excreted by the kidney, collect 6 hours urine to determine its excretion, can reflect the exocrine function of the pancreas, normal value: 55-75%. 6, barium meal X-ray whole gastrointestinal examination can understand the secretion and motor function of small intestine and related lesions, such as intestinal dilation, stenosis, mucosal fold changes, diverticula, fistula, etc.