Method for assaying coagulation in fluid samples
This invention is a disposable cartridge for use at the patient side to perform traditional coagulation assays on fresh whole blood or blood derivative samples. The cartridge, in use with an electronic analyzer allows a fluid sample to be metered and quantitatively mixed with reagents which activate the coagulation cascade. An artificial substrate for thrombin, the enzyme whose action results in clot formation is also provided. Clot formation is subsequently detected using a microfabricated sensor also housed within the cartridge which detects electrochemically the product of the thrombin reaction upon the synthetic substrate.
1. A method of determining a coagulation parameter in a sample using a single-use cartridge in combination with an analyzer, wherein the cartridge includes an entry port for receiving a sample, an entry port closure, a holding chamber in communication at a first end with the entry port, and a capillary stop in communication with the holding chamber at a second end, wherein the capillary stop is in communication with an analysis chamber containing a reagent, a conductimetric sensor sensitive to the displacement of a fluid sample across the conductimetric sensor and an amperometric sensor, wherein the holding chamber is in communication with an overflow chamber for receiving and retaining excess sample, wherein the overflow chamber is in communication with a pneumatic pump actuated by the analyzer, wherein the analyzer is capable of actuating the pneumatic pump to displace the sample from the holding chamber, the method comprising the steps of:
(a) applying the sample to the entry port;
(b) filling the holding chamber;
(c) closing the entry port;
(d) permitting excess sample to enter and be retained in the overflow chamber;(e) inserting the cartridge into the analyzer;
(f) actuating the pneumatic pump to deliver a metered portion of the sample into the analysis chamber;
(g) reacting the sample with the reagent in the analysis chamber;
(h) positioning the sample in the analysis chamber with respect to the conductimetric sensor;
(i) detecting a reaction product from the reagent at the amperometric sensor; and
(j) determining the coagulation parameter from an output of the amperometric sensor.
2. The method of claim 1 , wherein the coagulation parameter is selected from the group consisting of prothrombin time, activated partial thromboplastin time, activated clotting time, kaolin activated clotting time and celite activated clotting time.
3. The method of claim 1 , wherein in step (h) the sample is oscillated back and forth by the pneumatic pump using the output of the conductimetric sensor.
4. The method of claim 1 , wherein the cartridge comprises a hydrophobic area located between the analysis location and the holding chamber.
5. The method of claim 1 , wherein the volume of the sample is in the range of about 1 microliter to about 1 milliliter.