Patent ID: 7439069

Claim:
A system for performing a test on a blood sample determining a coagulation time comprising: a test cartridge comprising a blood receptacle that is open to the atmosphere into which a blood sample is to be deposited, a vacuum port that is open to atmosphere, and a spiral capillary within the test cartridge having a capillary length and cross-section area, a first capillary end of the spiral capillary open to the blood receptacle and a second capillary end of the spiral capillary open to the vacuum port, whereby the spiral capillary is closed to atmosphere; and a vacuum applicator having a vacuum applicator port adapted to be fitted to the vacuum port to close the vacuum port from atmosphere and further comprising: a vacuum applicator housing enclosing a vacuum chamber and extending between the vacuum applicator port and a vacuum cylinder; a piston fitted within the vacuum cylinder; a drive motor coupled to the piston adapted to be powered upon deposition of the blood sample in the blood receptacle to move the piston at a predetermined fixed rate within the vacuum cylinder that creates a vacuum in the spiral capillary sufficient to aspirate the blood in the receptacle along the spiral capillary toward the vacuum port until a blood clot is formed that blocks further blood aspiration; a pressure sensor coupled to the vacuum chamber that is operable to measure the vacuum within the vacuum chamber and develop an air pressure signal during movement of the piston; a pressure change detection circuit for comparing successive pressure signals to detect a change in pressure occurring when a blood clot blocks aspiration of blood through the spiral capillary and generate a clot detection signal; and a timer for timing the elapsed time from the commencement of the vacuum and generation of a clot detection signal, thereby determining a coagulation time.