A likely aetiology is?
a. Waldenström's macroglobulinaemia
b. Heparin
c. Sézary cell leukaemia
d. Pelger-Hüet anomaly
e. von Willebrand's disease
f. Haemophilia
g. HIV infection
h. DIC
i. Acanthocytosis
j. Vit K deficiency
answer is B,
thrombin is only prolonged by heparin or DIC.... platelets are normal, so not DIC
Why a normal INR? heparin mildly prolongs prothrombin time, it would require a big dose to cause an increased INR.... unlike warfarin.
• APTT: principally assesses the ‘intrinsic’ path of the coagulation cascade.
• PT or INR (monitoring warfarin therapy): assesses ‘extrinsic’ pathway.
• Thrombin time (TT): only used to differentiate between heparin contamination, dysfibrinogenaemia and DIC. This test is not used routinely and needs to be requested specifically.
• Bleeding time: tests platelet function. Now virtually obsolete.
• Fibrin degradation products (FDPs): Components released into the blood following clot degradation. Levels rise after any thrombotic event. Can be used to test for DIC. The most notable subtype of FDPs is D-dimer.
• D-dimer: principally used to screen adults for thrombotic disorders, e.g. deep vein thrombosis (DVT). Rarely used in children except possibly to help monitor management of DIC (possibly along with FDPs). Note: DIC is a clinical diagnosis and is not made my measuring D-dimers or
FDPs.
Warfarin:
Prothrombin time grossly prolonged, thrombin time normal, aPPT increased
Heparin:
Thrombin time prolonged, aPPT increased, prothrombin mildly increased
Vitamin K Deficiency
INR (PT) is elevated out of proportion to elevation of the aPTT
• decreased Factors II, VII, IX, X (vitamin K-dependent)
Hemophilia
Prolonged aPTT, low factor VIII, everything else normal
DIC
Low platelet count, prolonged aPTT, prothrombin time, thrombin time
Von Willebrand's
| Normal or prolongoned APTT, prolonged bleeding time |
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