title: γ/IgG ratio: role in distinguishing monoclonal spikes from fibrinogen.
abstract: Serum protein electrophoresis (SPEP) is a standard screening method for detecting monoclonal gammopathies. Presence of fibrinogen, however, can mimic a true monoclonal spike and interfere with accurate monoclonal protein identification. We describe a novel approach for distinguishing fibrinogen spikes from true monoclonal spikes. We classified 600 individual patient samples into four groups: group 1, 58 samples with a fibrinogen spike; group 2, 127 samples with a spike due to a monoclonal gammopathy; group 3, 181 samples with previously established monoclonal gammopathies but resolved posttreatment; and group 4, 234 control samples without monoclonal gammopathies. The value of using a γ region fraction/IgG ratio in distinguishing fibrinogen from true monoclonal spikes was assessed. The γ/IgG ratio in the fibrinogen group is significantly (P<0.0001) higher than this ratio in the other three groups. A γ/IgG ratio cut-off value of 1.13 discriminates true monoclonal gammopathies from fibrinogen. Moreover, exclusion of elevated IgA or IgM cases improves the ratio's predictive power. The probability cut-off is 0.756, corresponding to a γ/IgG ratio of 1 (93% sensitivity, 91% specificity). Using the γ/IgG ratio improves the screening power of SPEP and offers a simple and reliable diagnostic tool for distinguishing fibrinogen spikes from true monoclonal spikes.
authors.affiliation: Immunology Laboratory, Department of Pathology, Johns Hopkins University, School of Medicine, Baltimore, Maryland 21287, USA.
authors.forename: Maria Teresa
authors.initials: MT
authors.lastname: Lee
authors.forename: Patrizio
authors.initials: P
authors.lastname: Caturegli
authors.forename: Richard L
authors.initials: RL
authors.lastname: Humphrey
authors.forename: Richard E
authors.initials: RE
authors.lastname: Thompson
authors.forename: Barbara
authors.initials: B
authors.lastname: Detrick
mesh_terms: D000368:Aged; D001797:Blood Protein Electrophoresis / Q000379:methods* / Q000592:standards; D005260:Female; D005340:Fibrinogen / Q000032:analysis* / Q000737:chemistry; D006801:Humans; D007070:Immunoglobulin A / Q000097:blood / Q000737:chemistry; D007074:Immunoglobulin G / Q000097:blood* / Q000737:chemistry; D007075:Immunoglobulin M / Q000097:blood / Q000737:chemistry; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D010265:Paraproteinemias / Q000097:blood*; D012372:ROC Curve; D018709:Statistics, Nonparametric
chemical_list: D007070:Immunoglobulin A; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D005340:Fibrinogen