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. Electroimmunodiffusion (EID) or enzyme immunoassays (enzyme-linked immunosorbent assay; ELISA) are the commonly employed techniques for measuring protein S and C4b-binding protein (C4b-BP) immunologically. Procedures for these assays are time-consuming and labor-intensive. The introduction 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 immunoassay for total and free protein S (TPS, FPS) and C4b-BP, using the light-scattering mode, on the Automated Coagulation Laboratory (ACL) 300 Plus (Instrumentation Laboratory, Lexington, MA, U.S.A.). We also 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 coefficient 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 activity. 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 recovery was 94-109, 97-100, 91-103, and 99-103%, respectively, The normal ranges determined on plasmas from 30 healthy individuals were 113 +/- 37 (mean +/- 2 SD) for TPS, 106 +/- 35 for FSP, 111 +/- 22 for C4b-BP, and 107 +/- 34 for protein S activity. The results for the microlatex immunoassay and either the EID or the ELISA methods showed excellent correlations for FPS and C4b-BP; the correlations between LIATEST and either EID or ELISA for TPS were also relatively high. The functional activity of protein S correlated well with FPS. Microlatex immunoassays, using the light-scattering mode for TPS, FPS, or C4b-BP, and the functional assay of protein S can be adapted on the ACL 300 Plus system with a high accuracy and reproducibility and with considerable time saving.