Screening Test in Hematology

Tourniquet Test/ Rumpel Leede

• Determines capillary fragility, measures the endothelial support function of platelet and the strength of capillary wall
  
• By impeding venous flow to increase capillary pressure by a blood pressure cuff wrapped around the upper arm for a period of time
  

Platelet Count

• Determines the amount of platelet in blood volume
  
• Could be manually or using blood analyzer
  
• Reference range : 150,000-450,000 / uL
  

Platelet morphology

• When examining peripheral blood smears, platelet size and morphology should be observed
  
• Normal platelets are seen to contain a variable number of azurophilic granules concentrated in the center and surrounded by a clear area
  

Bleeding Time

• A sharp skin puncture is made and bleeding time is noted
  
• It measures interaction between platelets and injured vascular endothelium
  
• Reference value : 1-7 minutes
  
• Prolonged values are found in some vascular defects, qualitative and quantitative platelet abnormalities
  
• Purpose:
  
  • to screen patients with platelet dysfunction
    
• Principle:
  
  • The bleeding time is time (in minutes) that it takes for bleeding to cease from a small, superficial wound made under standardized condition
    
  • The bleeding time is mainly affected by primary hemostatic mechanism (platelet number & function), but is also affected by a variety other conditions
    
• Methods of bleeding time
  
• Duke method
  
  • using an ear lobe
    
  • normal range: 1-3 minutes
    
  • the reproducibility is poor
    
  • Ivy method
    
  • the skin of hand surface of forearm is incised
    
  • vein pressure is standardized by pressuring constantly to the upper arm
    
  • normal range: 1-7 minutes
    
  • Template Ivy method
    
  • a template and fixation plate for blade are used instead of a blade make a constant incision
    
  • normal range: 2-7 minutes (with 9 mm incision)
    

Prothrombin Time (PT)

• Purpose:
  
  • The PT assay is used to screen for inherited and acquired abnormalities in the extrinsic (factor VII) and common (factors V, X, protrombin and fibrinogen) pathways
    
  • The PT is also used to monitor the effect of oral anticoagulant therapy
    
  • Principle:
    
  • Clotting is initiated by a commercial tissue factor reagent, called thromboplastin, and calcium are mixed and the clotting time determined.
    
• Normal range (depend on reagent used)
  
  • 10-12 seconds
    
  • 12-14 seconds
    
• When patients are receiving oral anticoagulants, the ratio of the patient's PT to that of the normal control is useful in monitoring this therapy
  

Prothrombin Time (PT)

• Interpretation:
  
  • The common causes of prolonged PT are:
    
    • The administration of oral anticoagulant drugs (vit K antagonist/Warfarin)
      
    • Liver disease
      
    • Vitamin K deficiency
      
    • Disseminated intravascular coagulation
      
    • Deficiency of extrinsic coagulation factors
      
    • Inhibitor to F. VII
      

INR

• Control of oral anticoagulant
  
• Variation in reagent of PT
  
• Standardization of thromboplastin: ISI (International Sensitivity Index)
  

  
   

Activated Partial Thromboplastin Time (APTT)

Purpose:

• The APTT assay is used to detect inherited and acquired coagulation factor deficiency and quality of the intrinsic pathway, to screen for lupus anticoagulant and to monitor heparin therapy
  

Principle:

• The APTT is an assay of the intrinsic and common pathway. A platelet substitute (crude phospholipid), and a surface-activating agent such as micronized silica (to activate factor XII) are added to plasma. This achieves optimal contact activation
  
• Calcium is then added and the clotting time is recorded
  
• The APTT assay measures all factors except factors VII and XIII
  
• Activated Partial Thromboplastin Time (APTT)
  
• Normal range: depending on the reagent used
  
  • 25-45 seconds
    
  • 23-35 seconds
    

 

• The common causes of prolonged APTT are:
  
  • Disseminated intravascular coagulation
    
  • Liver disease
    
  • Massive transfusion with stored blood
    
  • Administration of heparin or contamination with heparin
    
  • A circulating anticoagulant
    
  • Deficiency of a coagulant factor other than factor VII
    
  • Inhibitor to intrinsic factors (e.g. antibody to f. VIII in hemophiliac)
    

Thrombin Time (TT)

• Purpose:
  
  • The TT is used to screen for abnormality in the conversion of fibrinogen to fibrin
    
  • Principle:
    
  • Thrombin is added to plasma and the clotting time measured
    
  • The TT is affected by the concentration & reaction of fibrinogen and the presence of inhibitory substances including fibrinogen/fibrin degradation products (FDP) and heparin
    
• Interpretation: normal 15-19 seconds
  
  • The common causes of prolonged thrombin time are:
    
    • Hypofibrinogenemia
      
    • Increased of FDP
      
    • Presence of heparin
      
    • Dysfibrinogenemia
      

Fibrinogen

• Quantity : fibrinogen concentration
  
• Quality : Thrombin time (TT)
  

Methods of PT, APTT , fibrinogen and TT test

• Manually: tilt tube
  
• Semiautomatic: coagulometer
  
• Fully automatic: coagulometer