PHYSICAL METHODS TO PREVENT BLOOD CLOTTING

PHYSICAL METHODS TO PREVENT BLOOD CLOTTING

Coagulation of blood is postponed or prevented by the following physical methods:

COLD

Reducing the temperature to about 5°C postpones the coagulation of blood.

COLLECTING BLOOD IN A CONTAINER WITH SMOOTH SURFACE

Collecting the blood in a container with smooth surface like a silicon-coated container prevents clotting. The smooth surface inhibits the activation of factor XII and platelets. So, the formation of prothrombin activator is prevented.

PROCOAGULANTS

Procoagulants or hemostatic agents are the substances which accelerate the process of blood coagulation. Procoagulants are:

THROMBIN

Thrombin is sprayed upon the bleeding surface to arrest bleeding by hastening blood clotting.

SNAKE VENOM

Venom of some snakes (vipers, cobras and rattle snakes) contains proteolytic enzymes which enhance

blood clotting by activating the clotting factors.

EXTRACTS OF LUNGS AND THYMUS

Extract obtained from the lungs and thymus has thromboplastin, which causes rapid blood coagulation.

SODIUM OR CALCIUM ALGINATE

Sosium or calcium alginate substances enhance blood clotting process by activating the Hageman factor.

OXIDIZED CELLULOSE

Oxidized cellulose causes clotting of blood by activating the Hageman factor.

TESTS FOR BLOOD CLOTTING

Blood clotting tests are used to diagnose blood disorders. Some tests are also used to monitor the patients treated with anticoagulant drugs such as heparin and warfarin.

1. Bleeding time

2. Clotting time

3. Prothrombin time

4. Partial prothrombin time

5. International normalized ratio

6. Thrombin time.

BLEEDING TIME

Bleeding time (BT) is the time interval from oozing of blood after a cut or injury till arrest of bleeding. Usually, it is determined by Duke method using blotting paper or filter paper method. Its normal duration is 3 to 6 minutes. It is prolonged in purpura.

CLOTTING TIME

Clotting time (CT) is the time interval from oozing of blood after a cut or injury till the formation of clot. It is

usually determined by capillary tube method. Its normal duration is 3 to 8 minutes. It is prolonged in hemophilia.

PROTHROMBIN TIME

Prothrombin time (PT) is the time taken by blood to clot after adding tissue thromboplastin to it. Blood is

collected and oxalated so that, the calcium is precipitated and prothrombin is not converted into thrombin. Thus, the blood clotting is prevented. Then a large quantity of tissue thromboplastin with calcium is added to this blood. Calcium nullifies the effect of oxalate. The tissue thromboplastin activates prothrombin and blood clotting occurs. During this procedure, the time taken by blood to clot after adding tissue thromboplastin is determined. Prothrombin time indicates the total quantity of prothrombin present in the blood. Normal duration of prothrombin time is 10 to 12 seconds. It is prolonged in deficiency of prothrombin and other factors like factors I, V, VII and X. However, it is normal in hemophilia.

PARTIAL PROTHROMBIN TIME OR ACTIVATED PROTHROMBIN TIME

Partial prothrombin time (PPT) is the time taken for the blood to clot after adding an activator such as phospholipid, along with calcium to it. It is also called activated partial prothrombin time (APTT). This test is useful in monitoring the patients taking anticoagulant drugs. It is carried out by observing clotting time after adding phospholipid, a surface activator and calcium to a patient’s plasma. Phospholipid serves as platelet substitute. Commonly used surface activator is kaolin.

Normal duration of partial prothrombin time is 30 to 45 seconds. It is prolonged in heparin or warfarin therapy (since heparin and warfarin inhibit clotting) and deficiency or inhibition of factors II, V, VIII, IX, X, XI and XII.

INTERNATIONAL NORMALIZED RATIO

International normalized ratio (INR) is the rating of a patient’s prothrombin time when compared to an

average. It measures extrinsic clotting pathway system. INR is useful in monitoring impact of anticoagulant drugs such as warfarin and to adjust the dosage of anticoagulants. Patients with atrial fibrillation are usually treated with warfarin to protect against blood clot, which may cause strokes. These patients should have regular blood tests to know their INR in order to adjust warfarin

dosage. Blood takes longer time to clot if INR is higher. Normal INR is about 1. In patients taking anticoagulant therapy for atrial fibrillation, INR should be between 2 and 3. For patients with heart valve disorders, INR should be between 3 and 4. But, INR greater than 4 indicates that blood is clotting too slowly and there is a risk of uncontrolled blood clotting.

THROMBIN TIME

Thrombin time (TT) is the time taken for the blood to clot after adding thrombin to it. It is done to investigate the presence of heparin in plasma or to detect fibrinogen abnormalities. This test involves observation of clotting time after adding thrombin to patient’s plasma. Normal duration of thrombin time is 12 to 20 seconds. It is prolonged in heparin therapy and during dysfibrinogenimia (abnormal function of fibrinogen with normal fibrinogen level).

Types and causes of purpura

Purpura is classified into three types depending upon the causes:

i. Thrombocytopenic purpura

Thrombocytopenic purpura is due to the deficiency of platelets (thrombocytopenia). In bone marrow disease, platelet production is affected leading to the deficiency of platelets.

ii. Idiopathic thrombocytopenic purpura

Purpura due to some unknown cause is called idiopathic thrombocytopenic purpura. It is believed that platelet count decreases due to the development of antibodies against platelets, which occurs after blood transfusion.

iii. Thrombasthenic purpura

Thrombasthenic purpura is due to structural or functional abnormality of platelets. However, the platelet count is normal. It is characterized by normal clotting time, normal or prolonged bleeding time but defective clot retraction.

3. von Willebrand Disease

von Willebrand disease is a bleeding disorder, characterized by excess bleeding even with a mild injury.

It is due to deficiency of von Willebrand factor, which is a protein secreted by endothelium of damaged blood vessels and platelets. This protein is responsible for adherence of platelets to endothelium of blood vessels during hemostasis after an injury. It is also responsible for the survival and maintenance of factor VIII in plasma. Deficiency of von Willebrand factor suppresses platelet adhesion. It also causes deficiency of factor VIII. This results in excess bleeding, which resembles the bleeding that occurs during platelet dysfunction or hemophilia.