• Coagulation Testing
  Link:practical-haemostasis.com
  
• Laboratory
• APTT
• Activated partial thromboplastin time
  - aka partial thromboplastin time with kaolin
• Tests common and intrinsic pathway
  - usual baseline 25-35s
• Used to monitor unfractionated heparin infusions
  - Usual target 1.5-2.5 x baseline
  
  Not used for LMWH or prophylactic UFH
• PT
• Prothrombin time
• Tests common and extrinsic pathway
  - usual baseline 11-15 seconds
• INR: international normalised ratio
• PT expressed as ratio of patient's PT vs control plasma
• Used to monitor warfarin treatment
  - usual therapeutic range 2.0-4.5 according to indication
• Heparin does not affect (reagent contains heparinase)
• Thrombin time
• Thrombin added to platelet-poor plasma
• Abnormal in states of reduced fibrinogen concentration or function
• Normal 14-16s
• Fibrinogen
• Factor 1
• Assay can be functional (Clauss assay), or derived from PT, clot weight, or based on presence of fibrinogen antigen
• Normal range 1.5-4.0 g/L
• Anti Xa levels
• Monitor patients on low molecular weight heparin
• LMWH binds to antithrombin and increases the extent to which it inhibits factor Xa (leading to anti-Xa activity)
• Peak levels 3-4 hours post dose
• Compare with reference curves, which vary with dose and agent
• Point of Care
  Link:www.anaesthesiauk.com/SectionContents.aspx?sectionid=147
  
• TEG
• Thromboelastography
• How it works:
  -Whole blood in rotating cup at 37 degrees, containing pin attached to torsion wire
  -When clot forms, rotational forces transmitted from cup to pin
  -Mechanical to electrical transducer creates image
• TEG Trace
• TEG
• R time:
  - Initiation of trace to 2mm
  - Soluble coag factors
  - Normal 4-8 min
• K time:
  - 2mm to 20mm
  - Measure of clot kinetics
• Alpha angle:
  - Angle to 2mm point from midline
  - Speed of fibrin plug formation
  - Normal 47-74 degrees
• Max amplitude:
  - Greatest height of trace
  - Clot strength - fibrinogen and platelets
  - Normal 55-73mm
• CL 30 and 60
  - Height of trace after 30 and 60 minutes
  - Measure of fibrinolysis and stability of clot
• Kaolin speeds clot formation (contact activator)
• Second cuvette contains heparinase, which eliminates effect of heparin, so can:
  -Assess other components of clotting while heparinised (eg CPB)
  -Compare with non-heparinase trace to establish whether heparin rebound has occurred / more protamine is required
• Whole blood, so reflect interactions between cells, platelets and factors
• - Expensive,
  - Lab tests remain gold standard
• - Expensive, lab tests remain gold standard
• - Quick result
  - May reduce unnecessary transfusion
• ROTEM
• Rotational thromboelastometry
• Similar to TEG, but:
  -Pin rotates in stationary cuvette
  -Meets increasing impedance as clot forms
  -Detected by optical system (LED, mirror, camera)
• Extem cuvette: contains tissue factor to assess extrinsic pathway
  
  Intem cuvette: contains contact activator to test intrinsic pathway
  
  Heparinase cuvette
  
  FIBTEM assesses fibrinogen contribution to clot strength (contains platelet inhibitor)
• Trace produced similar to TEG, but different parameter names and normal values
• Platelet Function Testing
• Platelets activators added to whole blood eg adrenaline, ADP)
  
  Different reagents for different causes of suspected platelet dysfunction (von Willebrands, COX inhibitors (aspirin), P2Y12 antagonists (clopidogrel), glycoprotein IIa/IIIb inhibitors (tirofiban)
• Platelet Function Analyser (PFA-100)
  - Time taken for hole in membrane to be 'plugged'
  
  Plateletworks
  -Non-aggregated platelets counted (should be zero)
  
  TEG platelet mapping
  -4 TEG cups with combinations of platelet activators, heparin, factor VIII and reptilase (similar to thrombin)
  
  Multiplate
  - Silver-coated wires - electrical impedance increases as platelets aggregate
  -5 adjacent test cells with reagents
• CoaguChekPro
  - INR, PT and aPTT
  -Whole blood activated with soybean and phospholipids
• ACT: Activated clotting time
• Used to monitor anti coagulation with unfractionated heparin
  - eg during cardiac surgery, ECMO
• Whole blood exposed to activator of intrinsic pathway
  -Normal range 90-150s
• Prolonged by:
  -Heparin
  -Warfarin
  -Aspirin and clopidogrel (variable effect)
  -Thrombocytopaenia
  -Factor deficiencies
  -Hypothermia
  -Haemodilution
• CEACCP
  Link:ceaccp.oxfordjournals.org/content/7/2/45.full.pdf