Urinary microalbumin measurement using a homogeneous liposomal immunoassay

• Published in: Journal of immunological methods 1996-08, Vol.194 (2), p.105-111
• Main Authors: Frost, S.J., Chakraborty, J., Firth, G.B.
• Format: Article
• Language: English
• Subjects: Albumins - immunology; Albuminuria - urine; Animals; Antialbumin antiserum; Biological and medical sciences; Colorimetry; Complement; Fab′ fragment; Fundamental and applied biological sciences. Psychology; Fundamental immunology; Humans; Immunoassay - methods; Immunoglobulin Fragments; Liposomes; Microchemistry - methods; Molecular immunology; Reference Standards; Rhodamines; Sensitivity and Specificity; Sheep; Sulforhodamine B dye; Techniques
• ISSN: 0022-1759; 1872-7905
• DOI: 10.1016/0022-1759(96)00057-9

A homogeneous colorimetric immunoassay which has been developed for urinary microalbumin utilizes complement-mediated immunolysis of liposomes containing the dye, sulphorhodamine B. Unlike a previously described model complement-mediated liposomal assay for serum albumin (Frost et al., 1994) which was competitive, this assay uses a sandwich-type format and Fab′ (antialbumin)-coated liposomes to increase the assay sensitivity. The liposomal assay, performed using a Cobas Bio analyser (Roche, Welwyn Garden City, UK), gave an acceptable correlation with a radioimmunoassay (NETRIA, London, UK): r = 0.94; y (liposomal assay) = 1.09 x (radioimmunoassay) − 1.54 mg/l. The imprecisions of the assays were similar and matrix effects due to the use of urine samples were determined to be acceptably small. The assay demonstrates the advantage of using Fab′-coated liposomes in sandwich-type liposomal immunoassays over liposomes coated with intact antibody, which failed to elicit complement-mediated immunolysis.