Microparticle-enhanced nephelometric immunoassay of lactoferrin in human milk.

A microparticle-enhanced nephelometric immunoassay was developed for lactoferrin quantitation in human milk. It is based on the nephelometric measurement of the light scattered during the competitive immuno-agglutination of a microparticle-lactoferrin conjugate with an antilactoferrin antiserum. This immunoassay is sensitive (detection limit in reaction mixture, 0.2 mg/L) and can be performed in diluted milk (1/3,000 in reaction mixture), excluding any interference or sample pretreatment. It allowed the quantification of lactoferrin on a large range of concentrations (0.675-21.6 g/L) with accuracy (linear recovery in dilution-overloading assay) and precision (within- and between-run coefficients of variation from 3% to 6%). Changes in the lactoferrin concentration of human milk during lactation were determined in 190 samples. The concentration and ratio of lactoferrin vs. total protein were found to be significantly higher in colostrum (5.9 g/l, 29%) than in transitional milk (2.9 g/L, 22%) or mature milk (2.5 g/L, 24%).