Photoelectric Determination of Plasma Clotting Times

A photoelectric clot timer is described. The apparatus allows a large analytic capacity, with good precision and correlation to manual methods, and can be used with capillary blood. Prothrombin analysis according to the method of Quick and Owren, the Thrombotest method, and determinations of partial thromboplastin time are ap-plicable to the apparatus. The semiautomated procedure is extremely simple, and the results are independent of the technicians performing the test. THE DETERMINATION OF plasma clotting times in various modifications has become an important and increasing part of the routine work in the clinical laboratory. The wide application of anticoagulant therapy in clinical surgery and medicine has resulted in many requests for pro-thrombin determinations. These procedures are a challenge to the capacity and precision of the laboratory and put physical and mental strain on the technicians performing the determinations by manual methods. Several attempts to automate the determination of clotting times have been made to obtain a simple procedure disengaged from the in-dividual ‘s reflex reaction time and subjective estimate of the point of coagulation, as well as a larger analytic capacity without loss of precision. Two principles have been in use in the development of clot-timers: (1) the electro-mechanical principle, where the timer is started manually and stopped by the formation of insoluble fibrin network in the reaction mixture, which serves to complete an electrical circuit through the clot detection system; and (2) the photoelectric principle, where the clotting end-point is assessed by means of the optical changes of the reaction mixture, which occur immediately before the actual clotting is visible to the eye. As in the electro-mechanical systems the timer must be started manually. Serious objections can be raised against the instruments which hav