HEMA 2 LE 1

• Hemostasis is the process that controls bleeding or the arrest of bleeding.
• Hemostasis deals with the coagulation and fibrinolytic mechanisms, as well as platelets.
• Hemostasis stops bleeding in the injured site at the same time as it maintains blood in a fluid state within the vascular compartment.
• Hemostasis is a complex interaction between blood vessels, platelets and biochemical reactants and factors in the plasma.
• When a blood vessel is damaged, the body responds by vasoconstriction, which allows the platelet contact activation.
• Platelets adhere to the injured surface and aggregate to form a basic hemostatic plug.
• Coagulation is initiated via the intrinsic system through the activating effect of a plasma factor (factor XII) reacting with the exposed collagen and elastin and by substances released into the blood by platelets and injured tissue cells (extrinsic system).
• The end product of coagulation is the fibrin clot which seals the vessel more securely with another plasma factor (factor XIII).
• When there is a wound, there is collagen exposure, so when there is collagen exposure tissue factor, tissue thromboplastin, will be released.
• Platelets will try to compensate by adhering to the area of injury.
• The tissue factor that is present will also form the blood coagulation cascade.
• This platelet adhesion will help in platelet activation which secretes substances like serotonin which aids in vasoconstriction to stop bleeding.
• To maintain this effect, samples should remain in unopened tubes if testing is not done immediately.
• Factors VII-proconvertin & XI, plasma thromboplastin antecedent tend to be prematurely activated at refrigerated temperature.
• Vigorous shaking must be avoided.
• Using Catheter:

  It may be necessary to discard as much as 30 mL, especially if thrombin clotting time is determined.
• Drawing blood from the catheter is not recommended, but if done, the first blood should be drawn into a syringe or evacuated tube and discarded before the specimen is obtained for coagulation tests, the volume discarded is dependent on the length and diameter of the catheter.
• Red cells have a buffering effect that helps to stabilize the pH.
• Sometimes only capillary blood can be obtained from a patient, and a PT test done on such blood is probably reliable provided the sample is obtained rapidly and anticoagulated immediately.
• It is recommended that this sample be avoided for coagulation studies.
• Changes in pH can affect values causing prolongation of clotting times, the buffered citrate contained in evacuated tubes protects samples against such loss.
• The needle is still in the vein and the needle holder is still attached, with a plastic syringe attached to the needle.
• Normal samples collected in evacuated tubes and stored at room temperature (unopened) for as long as 6 hours show no significant changes in PT or APT.
• Cases of congenital bleeding disorders and hemophilia need satisfactory venous sample for accurate diagnosis.
• If samples are left at room temperature for an extended time, factors V-proaccelerin & VIII are likely to deteriorate.
• After venipuncture, the needle is removed from the syringe and blood is allowed to run down the side of the tube to avoid hemolysis.
• Samples are transferred to tubes containing anticoagulants, stoppered and mixed thoroughly by inverting tube 10 times.
• Blood is drawn into this syringe and dispensed into appropriate tubes for any additional platelet function tests.
• Aldolase, lactase dehydrogenase, and blood bank tests may be invalidated by hemolysis.
• In coagulation studies, once the vein is entered, the tourniquet should be released immediately.
• Causes of hemolysis can be physiological or technical.
• A non-traumatic venipuncture is the goal anytime blood is drawn, especially when collecting samples for coagulation studies, but the quality of the sample is important to the accuracy of test results.
• Labile factors (V-proaccelerin & VIII-AHF) will deteriorate if left at room temperature for an extended period.
• Vigorously shaking the tube of blood, using a needle that is too small, drawing too hard on the syringe plunger, expelling blood too quickly through the syringe into the collection tubes, allowing the specimen to overheat, transfusion reaction, autoimmune hemolytic anemia, paroxysmal nocturnal hemoglobinuria, and disseminated intravascular coagulation are causes of hemolysis.
• Contamination with tissue thromboplastin (factor III) is a potent clot-activating substance found in fluids that escape from injured cells & tissue spaces, activating the extrinsic pathway of clotting and causing erroneous test results.
• Potassium increases in value due to hemolysis.
• Cold tends to activate factors VII-proconvertin & XI prematurely.
• Contact Group is involved in the intrinsic coagulation pathway and is moderately stable, not consumed during coagulation, and consists of factors XI, XII, prekallikrein and HMWK.
• Premature activation of the clotting process can occur before the sample can be evaluated in the test procedures.
• Hemolysis causes factors V-proaccelerin & VIII-AHF to deteriorate, and if it occurs in the blood drawing process, technical problems are usually the cause.