A performance evaluation of commercial fibrinogen reference preparations and assays for Clauss and PT-derived fibrinogen

The wide availability of fibrinogen estimations based on the prothrombin time (PT-Fg) has caused concern about the variability and clinical utility of fibrinogen assays. In a multi-centre study, we investigated fibrinogen assays using various reagents and analysers, Clauss assays generally gave good agreement, although one reagent gave 15-30% higher values in DIC and thrombolysis. Two commercial reference preparations had much lower potencies than the manufacturers declared, and plasma turbidity influenced parallelism in some Clauss assays, PT-Fg assays gave higher values than Clauss and showed calibrant dependent effects, the degree of disparity correlating with calibrant and test sample turbidity. Analyser and thromboplastin dependent differences were noted. The relationship between Clauss and PT-Fg assays was sigmoid, and the plateau of maximal PT-Fg differed by about 2 g/l between reagents. ELISA and immunonephelometric assays correlated well, but with a high degree of scatter. Antigen levels were higher than Clauss, but slightly lower than PT-Fg assays, which appeared to be influenced by degraded fibrinogen. Clauss assays are generally reproducible between centres, analysers and reagents, but PT-Fg assays are not reliable in clinical settings

Plasma fibrinogen

Fibrinogen is the major plasma protein coagulation factor. Low plasma fibrinogen concentrations are therefore associated with an increased risk of bleeding due to impaired primary and secondary haemostasis. Fibrinogen is a classical positive acute-phase reactant protein and is an independent predictor of coronary heart g disease events. This review considers available methods for measurement of fibrinogen and makes recommendations as to their appropriate use. Total clottable fibrinogen assays are the definitive and reference method for plasma fibrinogen measurement. However, they are time-consuming and are rarely required in clinical practice. Clotting rate assays remain the routine method of choice for investigation, monitoring and treatment of bleeding disorders associated with low plasma fibrinogen concentrations. They are appropriately sited in haematology or haemostasis laboratories, with facilities for further relevant investigations, and expert advice from consultant haematologists on appropriate management. They have also been used in the majority of studies investigating increasing fibrinogen concentrations as a cardiovascular risk factor. Prothrombin-time derived assays are widely used, because they are less expensive and come at no extra cost with prothrombin time assays. However, their results vary widely with analysers and reagents, show discrepancies with Clotting rate assays for both low and normal plasma fibrinogen samples, and at present they are not recommended by routine clinical use. Immunoassays (radial immunodiffusion, enzyme-linked immunosorbent assay or nephelometric) are useful in (a) differentiating hypofibrinogenaemia from dysfibrinogenaemia, and (b) assessing cardiovascular risk and acute-phase reactions. Unlike clottable fibrinogen assays, immunoassays can be performed in dipotassium edetate anticoagulated samples

Molecular phylogenetics and historical biogeography of Rhinolophus bats

The phylogenetic relationships within the horseshoe bats (genus Rhinolophus) are poorly resolved, particularly at deeper levels within the tree. We present a better-resolved phylogenetic hypothesis for 30 rhinolophid species based on parsimony and Bayesian analyses of the mitochondrial cytochrome b gene and three nuclear introns (TG, THY and PRKC1). Strong support was found for the existence of two geographic clades within the monophyletic Rhinolophidae: an African group and an Oriental assemblage. The relaxed Bayesian clock method indicated that the two rhinolophid clades diverged approximately 35 million years ago and results from Dispersal Vicariance (DIVA) analysis suggest that the horseshoe bats arose in Asia and subsequently dispersed into Europe and Africa. © 2009 Elsevier Inc. All rights reserved.Articl