Performance Evaluation of an ELISA for the Quantitative Measurement of α1-Antitrypsin in Stool

Background: The diagnosis of protein-losing enteropathy is aided by themeasurement of α1-antitrypsin (A1A) in stool and serum to calculate A1A clearance. The objective of this studywas to determine the performance characteristics of an ELISA for the measurement of A1A in stool and to determine reference limits for stool A1A and A1A clearance. Methods: A1A in stool was measured with a polyclonal antibody-based ELISA. Assay imprecision, analytical sensitivity, linearity, accuracy, analyte stability, and reference intervals were determined. Results: Within-run and total CVs were 5.4% and 6.5% and 13.8% and 14.5% at 17.3 and 66.9 ng/mL, respectively. The limitofquantificationwas2.0ng/mL, and theassaywas linear to85ng/mL.Meanrecovery ofA1Aaddedtosampleswas108.2%.A1Awasstable instool foraminimumof2days, 7days, and3months at roomtemperature, 4–8 °Cand−20 °C, respectively. Theupper 95thpercentile reference limits forA1A in stool and A1A clearance were 0.48 mg/g and 49mL/day, respectively. Conclusions: The A1A ELISA demonstrates acceptable performance for quantifying A1A in stool. The assay can be used in conjunction with serum A1A measurements for determining A1A clearance.