Fibrinogen is a major cardiovascular disease risk factor and is an independent predictor of coronary heart disease and stroke. Normal reference levels are approximately 2 to 4 g/L. Elevated levels are associated with the occurrence of cardiovascular disease-related events. The risk of increased bleeding in major surgery is inversely correlated with fibrinogen concentrations for concentrations below the upper limit of the reference interval, i.e., <4 g/L. Determination of the clottable fibrinogen concentration in plasma is, thus, important for the investigation of coagulation disturbances in patients. A novel assay for monitoring plasma fibrinogen content has been developed on the basis of a simple, single use lateral flow microfluidic device. A 15 microL plasma sample is applied to and travels along the microstructured device where it comes into contact with a thrombin reagent. This induces conversion of the soluble fibrinogen to insoluble fibrin and brings about clot formation. Lateral sample flow is arrested as a result of clotting, and the distance along the device at which this occurs has been shown to be dependent on the fibrinogen concentration. The test range was from 1 to 7 g/L of fibrinogen in undiluted patient plasma, and a result could be obtained within 5 min.