SOLID-PHASE COMPETITIVE LUMINESCENCE IMMUNOASSAY FOR IMMUNOGLOBULIN-AIN FECES - DEVELOPMENT AND CLINICAL VALIDATION

We describe a new simple solid-phase competitive luminescence immunoas say (LIA) for the determination of immunoglobulin A (IgA) in faeces. T he assay utilizes an anti-alpha-chain IgA antibody which is coated to polystyrene beads and acridinium ester-labelled human IgA as tracer an d, therefore, measures both monomeric and polymeric IgA. Dilution reco very of an internal standard was 96, 100 and 103%. Interassay and intr a-assay coefficients of variation (C.V.) ranged from 4.5 to 12.9%. The upper limit of normal of faecal IgA in 122 healthy controls was found to be 300 mg/l IgA (mean 73 mg/l, specificity of 99.2%). Patients wit h inactive Crohn's disease (Crohn's disease activity index (CDAI < 150 , n = 14) had faecal IgA values up to 3317 mg/l (mean 1073 mg/l; P < 0 .0001). In the active group (CDAI > 150, n = 26) faecal IgA values ran ged from 49 to 4094 mg/l (mean 1253 mg/l; P < 0.0001). Patients with u lcerative colitis were divided into a group with active disease (n = 1 8) and a remission group (n = 16) with values up to 1843 mg/l faecal I gA (mean 486 mg/l; P < 0.0032) and up to 602 mg/l faecal IgA (mean 176 mg/l; P < 0.4833), respectively. We also studied patients with non-in flammatory diseases of the gut with this assay. This LIA has proved to be a reliable method for the determination of elevated faecal IgA con centrations and for the detection of pathological findings in the gast rointestinal tract, especially in Crohn's disease. (C) 1997 Elsevier S cience B.V.