Latex immunoassay of serum alpha-fetoprotein using polyethylene glycol pretreatment

A latex particle immunoassay has been developed for the determination of serum alpha-fetoprotein. The assay consists of incubating the serum sample for 30 min at 50 degrees C with latex particles coated with anti-alpha-fetoprotein immunoglobulin, then quantifying the remaining unagglutinated particles with an optical particle counter. The assay is fully automated with a sampling rate of 40/h. The interference from rheumatoid factor is eliminated by precipitation with polyethylene glycol (7% final concentration). The alpha-fetoprotein standard curve, prepared in a human serum matrix, extends from 0.5 to 32 micrograms/l. Because sera are diluted ten-fold, the limit of detection of the assay lies around 5 micrograms/l. Coefficients of variation ranged from 4 to 15% and the recovery of alpha-fetoprotein tested on eight normal sera and four sera containing rheumatoid factor averaged 102.2% (SD = 13.2). The correlation coefficient between latex immunoassay and radioimmunoassay, calculated from the assay of 138 samples was 0.98.