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

The diagnosis of protein-losing enteropathy is aided by the measurement of α1-antitrypsin (A1A) in stool and serum to calculate A1A clearance. The objective of this study was 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.

A1A in stool was measured with a polyclonal antibody-based ELISA. Assay imprecision, analytical sensitivity, linearity, accuracy, analyte stability, and reference intervals were determined.

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 limit of quantification was 2.0 ng/mL, and the assay was linear to 85 ng/mL. Mean recovery of A1A added to samples was 108.2%. A1A was stable in stool for a minimum of 2 days, 7 days, and 3 months at room temperature, 4-8 °C and -20 °C, respectively. The upper 95th percentile reference limits for A1A in stool and A1A clearance were 0.48 mg/g and 49 mL/day, respectively.

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.