Dextran and hydroxyethyl starch do not interfere with fibrinogen measurement if Clauss method with mechanical clot detection is used
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KeywordsDextran Fibrinogen Hydroxyethyl Ball Bearing Clot Formation
In an updated European guideline for the management of bleeding following major trauma, published in a recent issue of Critical Care, Rossaint and colleagues  recommended that thrombelastometry instead of other laboratory methods be used to measure fibrinogen. The authors stated that the Clauss method  overestimates fibrinogen concentration when colloids are given. This claim is supported by studies of patients receiving colloids in which fibrinogen was measured by an automated Clauss assay performed on an ACL-300R coagulometer (Instrumentation Laboratory, Bedford, MA, USA), which detects clot formation photo-optically . Automated coagulometers use different technologies to detect fibrin clot endpoints. Some coagulometers employ mechanical principles involving the movement of a metal hook or the clot impedance of a ball bearing in a magnetic field; others use photo-optical devices to measure changes in light transmission .
Recently, Adam and colleagues  analyzed plasma diluted with different proportions of saline or hydroxyethyl starch (HES). Fibrinogen concentration was over-estimated if the clotting time was measured photo-optically in samples diluted with HES. But fibrinogen measurements in analyzers that used mechanical clot detection endpoints were accurate. Fenger-Eriksen and colleagues  assessed the accuracy of fibrinogen measurements in different analyzers and different methods in plasma diluted in different proportions with saline, HES, and albumin. The authors found that the photo-optical measurement overestimated fibrinogen concentration but that mechanical detection did not. Thromboelastometry seems to be a rapid and accurate estimation of the level and function of fibrinogen but is not available in most centers. However, most laboratories can easily measure fibrinogen by the Clauss method using mechanical detection. We recommend that the European guidelines specifying the use of thrombo-elastometry over the Clauss method be revised and qualified accordingly.
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