α₁-antitrypsin excretion in stool in normal subjects and in patients with gastrointestinal disorders

Fecal clearance of plasma α₁-antitrypsin is used as a measure of protein leakage into the intestinal tract. In this study, the α₁-antitrypsin concentration in stool and the plasma clearance of α₁-antitrypsin in normal subjects and in a consecutive series of patients with chronic diarrhea, malabsorption, or unexplained hypoalbuminemia was determined. The normal subjects were studied in their usual state and also when they had diarrhea secondary to ingestion of lactulose, sorbitol, sodium sulfate, or phenolphthalein. The study first concluded that induced diarrhea can cause an increase in α₁-antitrypsin clearance; if this is not considered in establishing normal values, there may be an overdiagnosis of excess protein leakage in patients with diarrhea. Second, there is a highly significant statistical correlation (P < 0.001) between α₁-antitrypsin clearance and serum albumin concentration. On average, the serum albumin falls below 3.0 g/dL (30 g/L) when the α₁-antitrypsin clearance exceeds 180 ml/day, a value that is about threefold higher than the upper limit of normal. Third, three of nine patients with microscopic/collagenous colitis had elevated clearance of α₁-antitrypsin; by contrast, abnormal α₁-antitrypsin clearance was not found in 23 patients with idiopathic secretory diarrhea. Fourth, fecal α₁-antitrypsin concentration is not a reliable index of abnormal α₁-antitrypsin clearance.