A FUNCTIONAL PROTEIN-S AND MICROLATEX IMMUNOASSAY FOR PROTEIN-S AND C4B-BINDING PROTEIN ON THE AUTOMATED COAGULATION LABORATORY (ACL)-300-PLUS

Protein S can be determined by functional or immunological assays. Ele ctroimmunodiffusion (EID) or enzyme immunoassays (enzyme-linked immuno sorbent assay; ELISA) are the commonly employed techniques for measuri ng protein S and C4b-binding protein (C4b-BP) immunologically. Procedu res for these assays are time-consuming and labor-intensive. The intro duction of microlatex immunoassays (LIATEST system; Diagnostica Stage, Asnieres-Sur-Seine, France) has provided an alternative for rapid and reliable immunological determination. We have placed the microlatex i mmunoassay for total and free protein S (TPS, FPS) and C4b-BP, using t he light-scattering mode, on the Automated Coagulation Laboratory (ACL ) 300 Plus (Instrumentation Laboratory, Lexington, MA, U.S.A.). We als o placed a functional activity assay of protein S (STACLOT protein S; American Bioproducts, Parsippany, NJ, U.S.A.) on the ACL 300 Plus. The performance characteristics for the assays yielded a within-run coeff icient of variance (CV) of 2.5-4.6% (n = 13) for TPS, 4.0-4.8% (n = 13 ) for FPS, 1.9-3.0% (n = 11) for C4b-BP, and 2.3-5.9% for protein S ac tivity. The interrun CV was 2.1-5.7% (n = 24), 3.7-7.0% (n = 12), 2.6- 7.0% (n = 16), and 4.0-8.4% (n = 27), respectively. Analytical recover y was 94-109, 97-100, 91-103, and 99-103%, respectively, The normal ra nges determined on plasmas from 30 healthy individuals were 113 +/- 37 (mean +/- 2 SD) for TPS, 106 +/- 35 for FSP, 111 +/- 22 for C4b-BP, a nd 107 +/- 34 for protein S activity. The results for the microlatex i mmunoassay and either the EID or the ELISA methods showed excellent co rrelations for FPS and C4b-BP; the correlations between LIATEST and ei ther EID or ELISA for TPS were also relatively high. The functional ac tivity of protein S correlated well with FPS. Microlatex immunoassays, using the light-scattering mode for TPS, FPS, or C4b-BP, and the func tional assay of protein S can be adapted on the ACL 300 Plus system wi th a high accuracy and reproducibility and with considerable time savi ng.