Optical endpoint sensing in an automatic whole blood clotting timer

Abstract

Most clotting time estimations are performed manually, although attempts have been made previously to automate them. The two major methods for automatically detecting the formation of the gel-like clot are mechanical (viscometric) and optical. The latter is superior in terms of accuracy of timing and freedom from artefacts but can only be performed on blood plasma. This paper describes a device which combines centrifuging to remove red cells and optical sensing of clot formation into a single operation, therepy giving activated clotting times on a par with those obtained mechanically from whole blood. The system offers the advantage over mechanical sensing that no nondisposable parts come in contact with the blood thereby eliminating e major source of timing errors. The timer works with any liquid coagulation activator, and will also time plasma clotting. The two-chambered design of the cuvette allows the activator to be kept separate from the blood until rotor startup The start of centifugal action mixes the blood and activator and starts the time. Timing is stopped auto matically when the rate of increase of optical density in the plasma, owing to fibrin formation, reaches a predetermined fevel.