Haematology

Question 1

What is haemostasis, primary and secondary haemostasis?

Answer 1

Physiological process that stops bleeding at the site of an injury while maintaining normal blood flow elsewhere in the circulation.

Primary haemostasis - initial vessel spasm, platelet aggregation and fibrin formation which takes place over seconds and forms a platelet plug. (extrinsic pathway)

Secondary haemostasis - clot formation which incorporates protease cascades of clotting factors and forms a fibrin clot. May take several minutes. (intrinsic pathway)

Question 2

What is thrombosis?

Answer 2

Inappropriate activation of clotting in uninjured vasculature or thrombotic occlusion following only minor injury

Question 3

What is anaemia?

Answer 3

Anaemia is defined as a Hb concentration below the expected value when gender, pregnancy and altitude have been taken into account

Question 4

Fibrinolysis

Answer 4

Process where fibrin clots are dissolved.
Plasmin - proteolytic enzyme degrading fibrin
- Produced in the liver as the precursor of plasminogen
- Conversion of plasminogen to plasmin stimulated by t-PA and urokinase

Question 5

TEG

Answer 5

Measurements made from the viscous and elastic properties displayed from the beginning of clot formation until fibrinolysis.

TEG - cup containing blood moves around suspended pin. Kept at 37oC

• R/ CT (4-8mins) - Reaction time. Start of sampling to initial fibrin formation (2mm), time to initial clot formation. Depends on clotting factors.
• K/ CFT (1-4mins) - end of R time (2mm) to 20mm, rate of clot formation, amplification phase, depends on fibrinogen
• a-angle (47-74o) - slope of trace from end of R, rate/speed of clot formation. Propagation phase, depends on fibrinogen.
• MA/ MCF (55-73mm) - max amplitude of trace (transition between coagulation and fibrinolysis), clot strength. Depends on plts (80%) and fibrin (20%)
• LY30/ Ll30 (0-8%) - amplitude of trace 30mins after MA, % of lysis 30mins after MA

Question 6

TRALI

Answer 6

Transfusion related lung injury

• FFP + plt > RBC

2 hit mechanism
- 1st = neutrophils in pt lung vessels are primed by cytokines
- 2nd = antibody in donor plasma activates the neutrophils -> release of cytokines, oxidises, proteases -> damage of pulmonary endothelium -> inflammatory oedema

Signs
- Non-cardiogenic pulmonary oedema

• Onset <6hrs after transfusion
• Incr risk with female donors

Question 7

Tranfusion reactions

Answer 7

Immediate
- Febrile non-haemolytic
- Febrile haemolytic
- Anaphylaxis
- TRALI

Delayed
- Delayed haemolytic reaction
- Haemolytic disease of newborn
- Post transfusion purpura
- Immunomodulation
- Graft vs host

Question 8

Virchow’s triad

Answer 8

For thrombus formation (or factors that prevent blood clotting in intact vessels)

• Endothelial surface factors
• Blood flow
• Blood constituents