Is it the factor V assay or the factor V Leiden mutation test?
Factor V activity assay is rarely ordered
  • The most common purpose for ordering the factor V activity assay is to assist with the differential diagnosis of liver disease. This order is often generated in consultation with the Laboratory Medicine service. 
  • The factor V activity assay is also ordered to establish the presence of an inherited factor V deficiency. Congenital factor V deficiencies are rare and are associated with severe bleeding in infancy.
The factor V Leiden mutation test is ordered often

Is it the factor X (ten) activity assay or the anti-Xa heparin assay? 
The Factor X activity assay is rarely orderedThe factor X activity assay is used mostly to diagnose congenital factor X deficiency, a rare disorder that causes severe bleeding beginning in infancy. It may be ordered to detect vitamin K deficiency in consultation with Laboratory Medicine.

The anti-Xa heparin assay is ordered often

The anti-Xa test (anti-factor Xa, or anti-activated factor X) is used to monitor heparin therapy. It may be ordered to monitor standard, unfractionated heparin when the partial thromboplastin time (PTT) cannot be used, such as when the patient has a lupus anticoagulant. The anti-Xa heparin assay is the only test that works for monitoring low molecular weight heparin such as LovenoxÒ or FragminÒ, or the pentasaccharide fondaparinux, trade name ArixtraÒ.

Is it the protein C activity assay or the C-reactive protein test?
The protein C activity assay is ordered as part of the thrombophilia profile

C-reactive protein (CRP) is a marker of inflammation

  • The C-reactive protein assay is often called high sensitivity C-reactive protein or HSCRP to distinguish it from an obsolete semiquantative method now abandoned. HSCRP detects chronic low-grade inflammation and is reported in quartiles: 
    • 1st quartile:  0-0.04 mg/dL 
    • 2nd quartile:  0.05-0.08 mg/dL 
    • 3rd quartile:  0.09-0.20 mg/dL 
    • 4th quartile: > 0.20 mg/dL
  • HSCRP values in the fourth quartile confer a 2 to 4-fold increased risk of cardiovascular disease in apparently healthy individuals. 
  • The HSCRP assay is often ordered as part of a cardiovascular risk profile that includes homocysteine and plasma lipid analysis.
Is it the von Willebrand factor cleaving protease assay or the von Willebrand profile?
The von Willebrand factor cleaving protease assay tests for the presence of the endothelial cell enzyme ADAMTS13 related to thrombotic thrombocytopenic purpura (TTP).

  • ADAMTS13 is normally present in plasma. 
  • ADAMTS13 is typically decreased or absent from plasma in chronic recurring TTP. 
  • In acute TTP, ADAMTS13 is decreased or absent and an inhibitor to ADAMTS13 may be identified. 
  • ADAMTS13 levels are typically normal in hemolytic-uremic syndrome (HUS).
The von Willebrand disease profile is used to detect von Willebrand disease (VWD), caused by decreased or absent von Willebrand factor (VWF). The following assays are performed as part of the von Willebrand profile:

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