1. History

Key elements include:

• severity of bleeding
• duration of bleeding, lifelong versus new
• family history
• drug history
• what type of bleeding mucocutaneous vs muscle and joint bleeds
• surgeries and experience with past dental work
• menstrual and obstetric history
• delayed vs immediate
• need for transfusion or iron supplementation related to bleeding

2. Assays

Bleeding time: evaluates primary hemostasis

• Prolonged in platelet disorders (quantitative and qualitative), von Willebrand's disease, connective tissue disorders
• Controversial! Not very specific. Does not correlate with bleeding before procedures.

Prothrombin time PT (INR): measures the time taken for VIIa to complex with tissue factor (TF) to form a clot, i.e., the extrinsic pathway of coagulation

• Prolongation indicative of VII deficiency or VIIa inhibitor
• Congenital VII deficiency is rare and most cases are acquired in the context of liver disease or Vit K deficiency seen in newborn and with Vit K antagonists such as Warfarin

Activated Partial thromboplastin time (aPTT): measures the time taken for clotting in the intrinsic pathway

• Prolongation is indicative of:
  • factor deficiency (XI, IX, VIII)
  • Marked prolongation of XII deficiency but not associated with bleeding
  • Antiphospholipid antibody
  • Factor (VIII, IX, XI) inhibitor
  • Drug (heparin)

Prolongation of PT and aPTT

• Deficiency or or inhibitor of factors X, V, II (prothrombin), i.e., the common pathway factors
• Fibrinogen deficiency (<80 mg/dl)
• High doses of anticoagulants
• Elevated in DIC

Thrombin time

• Measures conversion of fibrinogen to fibrin by thrombin (IIa)
• elevated in DIC, dysfibrinogenemias or hypofibrinogenemias, heparin

Factor XII deficiency

• Bleeding without prolongation of PT or PTT
• High incidence of intracranial hemorrhage, umbilical stump hemorrhage and women with spontaneous abortions
• Does not prolong the aPTT so have screen for deficiency with clot solubility assay or assay for factor level

Factor Assay

• Quantitates the amount of factor in a given individual

Mixing studies

• Indicated for prolongation in PT or aPTT
• Allows one to determine whether elevation in these tests is causes by factor deficiency or inhibitor
• Patient's abnormal plasma is mixed in 1:1 ratio with normal plasma and abnormal test (PT or PTT) is repeated. Possible results include:
  • Normalization of aPTT or PT at time zero that remains normal at 2 hours is diagnostic of a factor deficiency or inhibitor of von Willebrand's factor (VWF)
  • Normalization at time zero with prolongation on incubation implies the presence of an inhibitor (an acquired antibody)
  • No or partial correction at time zero, with aPTT prolonging with incubation suggestive of antiphospholipid antibody

von Willebrand's screening

• Factor VIII assay
• VWF antigen (VWF:Ag) most commonly by ELISA
• Ristocetin cofactor activity (VWF:RCo)
• VWF multimer analysis

Inhibitor Assay / Bethesda Assay

• Serial dilutions of the patient's plasma mixed in 50:50 ratio with normal plasma, followed by assay for the factor that is being inhibited
• Expressed as a Bethesda titre with one Bethesda unit (BU) being the amount of the inhibitor (i.e., the dilution of the patient's plasma) that neutralizes 50% of the factor in the normal plasma

Other points

• Vit K dependent coagulation factors: II, VII, IX, X, protein C and Protein S
• Be aware that infants are deficient in Vit K dependent factors