Abstract
To determine α-fetoprotein (AFP) in human saliva, a highly sensitive sandwich enzyme immunoassay for saliva AFP was developed. AFP standards and saliva samples were added into the wells of a polystyrene plate coated with goat IgG antibody against human AFP. After incubation, the wells were washed and horseradish peroxidase-labelled antibody was added. The enzyme activity specifically bound to the well was assayed using 3,3′,5,5′-tetramethylbenzidine and hydrogen peroxide as substrate. The reaction was stopped by addition of 2 M sulphuric acid and the AFP concentration was determined from the absorbance at 450 nm. The minimum detectable concentration was 8 ng/L. The recovery of AFP mixed with human saliva was 91·1–102·4%. The within-assay and between-assay coefficients of variation were 6·5–8·9% and 7·6–10·8%, respectively. The assay correlated well with a radioimmunoassay for human AFP (r = 0·985, n = 13, P < 0·001). The mean concentration of AFP in normal human saliva was 14·3 ng/L (SEM = 4·9 ng/L, n = 10) and significantly higher levels of saliva AFP were observed in hepatocellular carcinoma patients with positive serum AFP (mean 1367·8 ng/L, SEM 595·4 ng/L, n = 6; P < 0·001). Strong correlation was observed between saliva AFP and serum AFP (r = 0·978, P < 0·01, n = 13).