title: Effect of specimen type on free immunoglobulin light chains analysis on the Roche Diagnostics cobas 8000 analyzer.
abstract: The measurement of free immunoglobulin light chains is typically performed on serum; however, the use of alternative specimen types has potential benefits. Using the Freelite™ kappa and lambda free light chains assay on a Roche Diagnostics cobas 8000 c502 analyzer, we compared three specimen types (serum, EDTA-plasma and lithium heparin plasma separator gel-plasma) on 100 patients. Using Deming regression and eliminating outliers (limiting data to light chain concentrations below 400 mg/L), the three specimen types showed comparable results for kappa light chain concentration, lambda light chain concentration, and kappa/lambda ratio with slopes close to 1.0 and y-intercepts close to zero. EDTA-plasma showed slightly more positive bias relative to serum than lithium heparin. Analysis using EDTA-plasma and lithium heparin plasma showed comparable linearity, precision, and temperature stability. A single sample showing hook effect (not in the comparison set) gave comparable results using either plasma specimen type. For the Freelite™ kappa and lambda free light chains assay, both EDTA-plasma or lithium heparin-plasma can serve as acceptable substitutes for serum, at least for the Roche cobas 8000 analyzer.
authors.affiliation: Department of Pathology, University of Iowa Hospitals and Clinics, Iowa City, IA 52242 USA.
authors.forename: Louis S
authors.initials: LS
authors.lastname: Nelson
authors.affiliation: Department of Pathology, University of Iowa Hospitals and Clinics, Iowa City, IA 52242 USA.
authors.forename: Bryan
authors.initials: B
authors.lastname: Steussy
authors.affiliation: Department of Pathology, University of Iowa Hospitals and Clinics, Iowa City, IA 52242 USA.
authors.forename: Cory S
authors.initials: CS
authors.lastname: Morris
authors.affiliation: Department of Pathology, University of Iowa Hospitals and Clinics, Iowa City, IA 52242 USA.
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Krasowski
keywords: Immunoglobulin light chains; Laboratory automation; Nephelometry; Plasma; Serum