Solid phase competitive luminescence immunoassay for immunoglobulin A in faeces: development and clinical validation

Area of Science:

• Clinical Chemistry
• Immunology
• Gastroenterology

Background:

• Elevated levels of immunoglobulin A (IgA) in faeces are indicative of gastrointestinal inflammation.
• Accurate and reliable methods are needed for quantifying faecal IgA to aid in diagnosing and monitoring inflammatory bowel diseases.

Purpose of the Study:

• To develop and validate a simple, solid-phase competitive luminescence immunoassay (LIA) for the determination of immunoglobulin A (IgA) in faeces.
• To assess the utility of this LIA in distinguishing between healthy individuals and patients with inflammatory gastrointestinal conditions, particularly Crohn's disease.

Main Methods:

• A solid-phase competitive luminescence immunoassay (LIA) was developed using anti-alpha-chain IgA antibody-coated polystyrene beads and acridinium ester-labelled human IgA as a tracer.
• The assay measures both monomeric and polymeric forms of IgA.
• Validation included dilution recovery, inter-assay, and intra-assay coefficient of variation (C.V.) assessments.

Main Results:

• The assay demonstrated good dilution recovery (96-103%) and acceptable C.V.s (4.5-12.9%).
• The upper limit of normal faecal IgA in healthy controls was 300 mg/l (specificity 99.2%).
• Significantly elevated faecal IgA levels were observed in patients with inactive (mean 1073 mg/l) and active Crohn's disease (mean 1253 mg/l), and active ulcerative colitis (mean 486 mg/l) compared to controls.

Conclusions:

• The developed luminescence immunoassay (LIA) is a reliable method for quantifying faecal immunoglobulin A (IgA).
• This assay effectively detects elevated faecal IgA concentrations, proving valuable for identifying pathological findings in the gastrointestinal tract.
• The LIA shows particular promise for the detection and monitoring of Crohn's disease.