Clotting Time - Section 2 - MISR University PDF

Clotting Time Section 2 Introduction Indication Principle Methods Precautions Interpretation  Hemostasis components Blood vessels vasoconstriction Platelets primary hemostasis Coagulation system...

Clotting Time Section 2 Introduction Indication Principle Methods Precautions Interpretation  Hemostasis components Blood vessels vasoconstriction Platelets primary hemostasis Coagulation system secondary hemostasis Fibrinolysis clot destruction  Coagulation system (secondary hemostasis) It involves a series of reactions through a cascade like process that concludes with the formation of an insoluble fibrin clot to insure stability of the initially loose platelet plug. Clotting is initiated with the activation of two pathways that lead to fibrin formation: Intrinsic pathway Extrinsic pathway (contact between blood and (tissue factor) collagen or other substances)  Clotting Time It is the time required for blood to form a clot, it is a rough measure of all intrinsic clotting factors in the absence of the tissue factor. indications: Clotting time test is used in diagnosis of coagulopathy and to monitor heparin therapy. coagulopathy Is a condition in which the blood's ability to clot is affected. Coagulopathy may be congenital (such as hemophilia) or acquired (caused by a defective synthesis of plasma coagulation factors)  principle The whole blood will form a solid clot when removed from the vascular system and exposed to a foreign surface such as a glass tube. The surface of glass tube initiate the clotting process by activation of the intrinsic pathway, that requires only exposing factor XII to thrombogenic surface e.g glass. Thrombogenicity can be defined as tendency of a material to generate blood clotting or thrombus, when in contact with the blood.  Methods Lee and White’s Method Slide Method  Lee and White’s Method Materials:- 1- equipment for collection of blood. 2- Stopwatch. 3- dry, clean glass test tubes. 4- water bath. Specimen:- Fresh venous blood sample.  procedures: ▪ Make a clean venipuncture then draw 3-5ml of blood. ▪ Start the stopwatch as soon as the blood enters the syringe. ▪ Label 3 glass test tubes and number them from 1-3 (the third tube is considered as control). ▪ Place about 1ml of blood in each of three test tubes. ▪ Place the tubes in a stand so that they remain upright and undisturbed in the water bath. ▪ After 4 minutes take the first tube from water bath and tilt gently to a 45 angle to see whether the blood has clotted. ▪ If blood not clotted return it to the water bath. ▪ After that examine the first two tubes alternately at 30 seconds intervals. ▪ After the blood in the first two tubes has clotted examine the third tube (control) immediately. ▪ Average value of the results in the 3 tubes is taken as the clotting time.  precautions The venipuncture must be without trauma to avoid contamination with tissue thromboplastin. Avoid haemolysis of the sample. Vigorous agitation of the tubes will significantly shorten the clotting time. Bubles entering the syringe when the sample obtained increase the rate of clotting. The blood should be allowed to flow gently down the inside of the test tube and not forcefully squirted into the test tube. More accurate and standard This test is time consuming. method. There are many variables in this technique  Slide Method Materials:- 1-Glass slide. 2-Alcohol swab. 3-Lancet. 4-Stopwatch. Specimen:- - Capillary blood  procedures: Sterilize the tip of a finger with alcohol swap and let to dry. Prick tip of finger by lancet. Apply 2-3 drops of the blood on slide and start stop watch. After 3 minutes start pulling blood from bottom to upward by lancet every 30 seconds until thread like structure appears. Stop the watch, record the total time.  It can be performed when This method is insensitive venous blood cannot be and unreliable. obtained. Normal clotting time (CT) The expected range is 4 to 11 minutes.  As the CT test is insensitive in the diagnosis of bleeding disorders, it has been replaced by PTT test. Disadvantages of clotting time test This test is only prolonged in severe deficiency of coagulation factors. It is insensitive to detect mild conditions of bleeding. Normal clotting time does not rule out coagulation abnormalities.  Interpretation The common causes of a prolonged CT are as follows: Deficiency of a coagulation factor other than factor VII. Disseminated intravascular coagulation(DIC). Administration of heparin or other anticoagulants. Liver disease.