To describe a new, quantitative, and reproducible method for detecting deposits of amyloid A protein in aspirated fat tissue and to compare it with smears stained with Congo red.
After extraction of at least 30 mg of abdominal fat tissue in guanidine, the amyloid A protein concentration was measured by a monoclonal antibody-based sandwich ELISA.
The concentrations in 24 patients with arthritis and AA amyloidosis (median 236, range 1.1-8530 ng/mg tissue) were higher (p < 0.001) than in non-arthritic controls, uncomplicated rheumatoid arthritis, and other types of systemic amyloidosis (median 1.1, range 1.1-11.6 ng/mg tissue). Patients with extensive deposits, according to Congo red staining, had higher concentrations than patients with minute deposits.
This is a new, quantitative, and reproducible method for detecting deposits of amyloid A protein in aspirated fat tissue of patients with arthritis, even when minute deposits are present as detected in smears stained with Congo red.