An automated test for rheumatoid factor

Abstract

A continuous flow system utilizing a plasma fraction Il-charcoal suspension for the detection and quantitation of rheumatoid factor has been developed. Tests indicate that the reactivity levels of the automated procedure and those of manual latex particle technics are comparable. Interestin automated laboratory procedures prompted study of a system to detect and quantitate rheumatoid factor (RF) using a charcoal indicator in a continuous flow system. Automated Reagin (AR) equipment (1,2) and test reagents, plasma fraction I1 and standardized charcoal, were studied to provide a test of suitable reactivity. This report describes the test, illustrates the serologic sensitivity and specificity of the technic and notes advantages of the automated procedure. MATERIALS AND METHODS Latex tests.A slide macroscopic test" and a quantitative latex fixation FII-LP procedure (3) were used as standard tests for rheumatoid factor (RF) . sions were added to heated (30 min a t 56" C) serum dilutions 1:20-1:5120. After incubation for 90 min at 56" C and then overnight at 5" C, the mixtures were centrifuged and examined for agglutination.I n addition to 750 specimens selected by latex tests, the following heated sera were studied: 92 reactive in a test for antinuclear antibody (4,5), 72 reactive in VDRL and fluorescent treponemal antibody-absorption (FTA-ABS) tests (6) , and 414 "normal" premarital specimens.Desiccated human plasma fraction 11 (FII)? and standardized charcoal (C$ were obtained. FII-C suspensions were prepared in glycine buffered 0.5% saline, p H 8.2. T h e flow-through system and serum diluent, dye markers and cleaning reagent were prepared and used accGrding to AR test procedures (1).Optimum concentrations of FII and C were established by machine titrations of FII-LP reactive and nonreactive sera. T h e serologic test r e s u h reported in this paper were ohtained with FII-C suspensions containing 5 mg FII and 0.25 mg C/ml. Preparations of 10 mg FII/ml were stored overnight a t 5" C and then heated 1 hr at 63" C. Five volumes were added to 1 volume of charcoal; the mixture was stirred 30 min, and 4 volumes of glycine buffer were added. Suspensions were stored at 5" C.