['Fibrinogen is a target of autoimmune reactions in rheumatoid arthritis (RA). Fibrin(ogen) derivatives are involved in inflammatory processes and the generation of a stable fibrin network is necessary for sufficient inflammation control. As the density and stability of fibrin networks depend on complex interactions between factor XIIIA (F13A) and fibrinogen genotypes, the authors studied whether these genotypes were related to C-reactive protein (CRP) levels during acute-phase reactions.', 'Association between α-fibrinogen (FGA), β-fibrinogen (FGB) and F13A genotypes with CRP levels was tested in two cohorts with longitudinal CRP measurements. Discovery and replication cohorts consisted of 288 RA (913 observations) and 636 non-RA patients (2541 observations), respectively.', 'Genotype FGB -455G>A (rs1800790) was associated with CRP elevations (≥ 10 mg/l) in both cohorts (RA, OR per allele 0.69, p=0.0007/P(adj)<0.015; non-RA, OR 0.70, p=0.0004/p(adj)<0.02; combined, OR 0.69, p<10(-5)/p(adj)=0.001). Genotype F13A 34VV (rs5985) was conditional for the association of FGB -455G>A with CRP as indicated by a clear restriction on F13A 34VV individuals and a highly significant heterogeneity between F13A 34VV and F13A 34L genotypes (p<10(-5), p(adj)=0.001). In both cohorts, mean CRP levels significantly declined with ascending numbers of FGB -455A alleles. Genotype FGA T312A (rs6050) exhibited opposite effects on CRP compared with FGB -455G>A. Again, this relation was dependent on F13A V34L genotype.'] Do fibrinogen and factor XIII A-subunit genotypes interactively influence C-reactive protein levels during inflammation?