Use of microtiter plates for latex agglutination immunoassay of serum alpha 2-macroglobulin.

A simple, sensitive turbidimetric immunoassay is described for analysis of alpha 2-macroglobulin (AMG) in serum, using microtiter plates and a commercial kit that features a sensitive latex reagent. Using microwells as reaction vessels and the latex reagent made it possible to minimize the sample size and the amounts of reagents. The procedure involves two pipetting steps and a brief incubation (10 min) at room temperature; the assay measures AMG concentrations ranging from 0.12 to 5 g/L and is unaffected by icterus, hemolysis, lipemia, or rheumatoid factor, even at high concentrations. Recovery of AMG added to three pooled serum samples averaged 95-105%. CVs for replicate analyses ranged from 1.9 to 4.8% (within-run) and 6.1 to 9.3% (between-run). Based on paired analyses of 70 serum specimens, AMG concentrations obtained by this turbidimetric microtiter immunoassay were in close agreement (correlation coefficient = 0.99) with results obtained by an enzyme-linked immunosorbent assay (ELISA). Serum AMG concentrations in 48 healthy adults (mean +/- 2SD) were 1.87 +/- 1.00 g/L.