Quantitative dot-blot enzyme immunoassay for serum amyloid A protein

A dot-blot enzyme immunoassay is described which tests for serum amyloid A protein (SAA) using a commercially available antiserum. Heat treatment of the serum caused a marked increase in the apparent concentration of SAA. Pre-heated serum was directly bound to a nitrocellulose membrane using 'Bio-Dot' microfiltration apparatus to ensure uniformity. Then the SAA was stained using an 'Immun-Blot' assay kit (Bio-Rad, Laboratories, U.S.A.), and the optical density of the stained SAA spots was measured directly by a densitometer. The detection limit was 1.25 micrograms/ml of apoSAA1 (an isotype of SAA) dissolved in fetal bovine serum. The method had sufficient sensitivity to measure SAA in 76% of normal subjects. The method is ideally suited to the rapid processing of a large number of samples (up to 96 samples) using only a small amount of the antiserum.