522 QUANTITATIVE FECAL ALPHA-1-ANTITRYPSIN TO MEASURE GASTROINTESTINAL PROTEIN LOSS

Excessive protein loss through the gastrointestinal tract is difficult to diagnose and quantitate because of the nonavailability of radiolabelled proteins and the disadvantages of their administration to children. Alpha-l-antitrypsin (α1AT) is an endogenous protein which is resistant to proteolytic digestion in the intestine, not found in the diet and as suggested by others should reflect plasma protein loss into the GI tract. We investigated its usefulness by measuring the fecal α1AT concentration in 24 patients with no malabsorption, 12 patients with cystic fibrosis (high fecal nitrogen), 10 patients with fat malabsorption only and 3 patients with protein-losing enteropathies. Stool aliquots were taken from 48-72 hour homogenized stool collections which had been evaluated for fecal fat. Five lambda samples were directly applied to and quantitated by radial immunodiffusion plates specific for anti-human αlAT (Boehringer-Mannheim). “Normal” daily αlAT loss expressed in mg/kg body wt/day was 1.70 ± 1.32 with similar values for cystic fibrosis (0.99 ± 0.68, p>0.05) and isolated fat malabsorption (1.51 ± 1.03, p>0.05). The α1AT loss for the 3 patients with protein-losing enteropathies (two with lymphangectasia, one undiagnosed) varied from 4.4-48 mg/kg per day and correlated with clinical criteria for protein loss. Conclusion: Fecal α1AT quantitation may be specific for measuring protein loss into the gastrointestinal tract.