Manual of basic techniques for a health laboratory - libdoc.who.int

9. Haematology 2979.9 Observation of clot retraction and measurement oflysis time9.9.1 PrincipleThe tubes with clotted blood are used:— for observation of the retraction of the clot— for measurement of the time it takes for the clot to dissolve (lysis).These tests are carried out for the diagnosis of certain haemorrhagic disorders.9.9.2 Materials●●●●Glass test-tubes, 75mm ¥ 10mm, marked to hold 1mlTimerMetal test-tube rackWater-bath● Materials to carry out venepuncture (see section 9.2.2).9.9.3 MethodCollection of specimensCollect a venous blood specimen from patients as described in section 9.2. Do notadd anticoagulant to the tubes in which you collect the blood.Observation of clot retraction1. Place the tube in the water-bath at 23°C (or leave it to stand at roomtemperature).2. Examine the clot after 1, 2, 3 and 4 hours. The clot normally remains solidduring the first 4 hours, although it begins to retract, usually in the first hour.After 4 hours the clot will have completely retracted, the red cell mass separatingfrom the yellow serum (Fig. 9.56).Measurement of lysis time1. Place the tube containing the blood in the water-bath at 37°C (or leave it tostand at room temperature).2. Examine the clot after 12, 24, 48 and 72 hours until lysis occurs; that is, until theclot dissolves completely and all the erythrocytes sink to the bottom of the tube(Fig. 9.57).Fig. 9.56 After 4 hours, examine the clot