Dr/Nahla Yacout 2016/2017

1. Tests for hemostasis (Practical) Physiology 232 BMS Dr/Nahla Yacout 2016/2017

2. Objectives • Enumerate tests for hemostasis • Explain Bleeding time test & its importance • Explain Clotting time test & its importance • Explain Clot retraction time test & its importance • Explain Clot lysis time test & its importance • Explain Prothrombin time (PT) test

3. Tests for hemostasis 1. Bleeding time 2. Clotting time 3. Clot retraction time (CRT) 4. Clot lysis time 5. Prothrombin time (PT)

4. Bleeding time Procedure: • Get a deep finger prick under aseptic conditions to get free-flowing blood • Note the time • Absorb the blood drops every 30 seconds by touching the puncture site with a filter paper, without pressing or squeezing the wound • Note the time when there is no blood spot on the filter paper N.B. Size of the blood spots gets smaller & smaller after the 1st or 2nd spot until there are no spots

5. Normal bleeding time = 1-5 minutes Bleeding time is prolonged in: Platelet deficiency – Vessel wall defects Bleeding time is normal in: Hemophilia Precautions: • The skin site for the test should be scrubbed well with alcohol to increase the blood flow • The skin should be dry & the puncture should be 3-4mm deep to give free flowing blood • Don’t squeeze on the puncture site • If bleeding continues for more than 10-12 min., you must stop the test & press a sterile gauze on the wound

6. Clotting time Procedure: 1. Draw 5ml venous blood by a new clean syringe …. This is the Zero time & then transfer the blood to a clean, dry test tube 2. Hold the test tube in a water bath at 37°C, take it out at 30 sec. intervals & tilt it ….. The end point is when the tube can be tilted without spilling the blood Normal clotting time: 5-10 minutes Clotting time is prolonged in: Deficiency in one or more of the clotting factors (Such as In case of hemophilia) – Liver diseases – Vitamin K deficiency

7. Clot retraction time (CRT) Procedure: 1. Transfer the test tube containing clotted blood to an incubator at 30°C. 2. Normally, the clot starts to shrink in about 30 min. …. Becomes half its size in 2-3 hours N.B. • Clot retraction depends on the release of many factors from the platelets, & so CRT depends on the platelet count • CRT is prolonged in case of: Low platelet count

8. Clot lysis time Clot lysis: Is a process by which a clot becomes fluid • Normally, the clot lysis in about 72 hours • More or less than this time is considered abnormal

9. Prothrombin time (PT)

10. PT For clotting to occur, • Prothrombin is converted into thrombin by (Prothrombin activator) • And then thrombin will convert fibrinogen into fibrin (Clot) The time required for clotting to occur is called: Prothrombin time (PT) Normal PT = 12 – 15 sec. Normal Level of prothrombin = 30-40 mg/dl Bleeding may occur if prothrombin level falls below 20% of normal PT test is used to control anticoagulant dose

11. PT PT is prolonged in case of: deficiency in certain clotting factors – High dose of oral anticoagulant – Vitamin K deficiency

12. What is the difference between bleeding time & clotting time??? Bleeding time: Tests platelet plug formation & the condition of the vessels Clotting time: Tests the formation of the clot Conditions in which bleeding time only is prolonged with normal clotting time: 1. Platelet deficiency (Low platelet count) 2. Defects in the function of platelets (Normal count but defect in function) 3. Defects in blood vessels walls

13. Conditions in which clotting time is increased: • Deficiency in one or more of the clotting factors • Vitamin K deficiency • Liver diseases Why does calcium deficiency not cause a bleeding disorder although it is essential in converting prothrombin to thrombin & making the clot???? Because only very small amount of calcium is required for clotting, & so bleeding because of calcium deficiency is not compatible with life