Coagulation Tests Health Article

Definition

Hemostasis has been described as "a process by which the body spontaneously stops bleeding and maintains blood in the fluid state within the vascular compartment." There are at least four major systems that are involved in this complex process: the vasculature system, the platelets, the fibrin-forming system, and the fibrin- lysing system. Hemostasis has also been further segregated into stages or steps. These are primary hemostasis, which is the interaction of the injured blood vessel and platelets; secondary hemostasis, which is referred to historically as the blood coagulation process; and tertiary hemostasis, which is the process of fibrinolysis (clot destruction). The first two stages are assessed by blood coagulation tests that evaluate platelets, circulating coagulation factors, and blood vessels.

Purpose

Coagulation tests are performed to aid in the diagnosis of bleeding disorders, monitor the effectiveness of anticoagulant therapy, and confirm a patient's blood clotting status prior to surgery.

Precautions

Before administering the test, the patient should be asked to list the medications he or she is taking, and whether or not he or she has recently experienced active bleeding, acute infection or illness, or undergone a blood transfusion, as these factors could adversely affect their coagulation test results. Some of the medications that can affect coagulation results include antacids, antibiotics, anticoagulants, antihistamines, aspirin, diuretics, nicotine, nonsteroidal anti-inflammatory drugs, oral contraceptives, steroids, tranquilizers, and vitamins C andK. If a patient is currently being medicated, the testing facility should be contacted to determine the acceptability of the blood sample. From the moment the blood specimen is drawn until the test is completed, the handling of the specimen is critical in coagulation studies. Assuming that the specimen is drawn correctly, the following procedures should be followed.

Collection of blood for coagulation tests

There is a generally held belief that the first tube in a case where multiple specimens are drawn should never be used for any hemostasis assay, because tissue thromboplastin from the initial venipuncture may affect coagulation test results. In addition, the tube(s) for coagulation testing should be filled before any tubes containing EDTA. If coagulation tests are the only studies ordered, a discard tube should be drawn before filling the blue- stoppered citrate tube used for the tests.