Fecal excretion of alpha 1-antitrypsin in patients with Crohn's disease. A comparison of nephelometry and radial immunodiffusion.

A comparison is made of two methods for quantifying fecal alpha 1-antitrypsin (A1ATF): nephelometry (NPL) (the method habitually employed in our laboratory), and radial immunodiffusion (RID). A method is also described for extracting A1ATF from single 24-hr stool samples. The normal A1ATF values were initially established in 25 healthy controls, followed by quantification of the protein in 30 patients with Crohn's disease, with the aim of evaluating the sensitivity and specificity of the test in assaying A1ATF and alpha 1-antitrypsin fecal clearance (CLAT). The precision of the measurement method and its applicability to the A1ATF extraction process are also evaluated. The ranges of normal A1ATF and CLAT values were found to be 0-42.2 mg/24 hr and 0-12.6 ml/24 hr, respectively; sensitivity was in turn 83% and 80% for A1ATF and CLAT, respectively, with a specificity of 100% in both cases. A good correlation was observed between the A1ATF quantifications afforded by RID and NPL in both the controls and patients with Crohn's disease (r = 0.917 and 0.997, respectively). We consider that A1ATF quantification is a rapid, safe, and reproducible method that is well tolerated by the patient.