Investigations
1st investigations to order
FBC
Test
Should be ordered before initiating prophylaxis. Acute drop in haemoglobin or severe thrombocytopenia is a contraindication to pharmacological thromboprophylaxis.
Result
acute drop in haemoglobin suggests active bleeding; severe thrombocytopenia increases risk of bleeding
serum creatinine
Test
Should be ordered before initiating prophylaxis. Severe renal insufficiency requires dose adjustment or use of an agent not excreted through the kidney.
Result
increased creatinine indicates severe renal insufficiency (creatinine clearance <30 mL/minute)
INR
Test
Should be ordered if a coagulation disorder is suspected. In this case, pharmacological prophylaxis could be contraindicated.
Result
variable; increased in some underlying coagulation disorders
PTT
Test
Should be ordered if a coagulation disorder is suspected. In this case, pharmacological prophylaxis could be contraindicated.
Result
variable; increased in some underlying coagulation disorders
Investigations to consider
serum antiplatelet factor 4 antibodies
Test
Should be ordered if clinical suspicion of heparin-induced thrombocytopenia while the patient is receiving unfractionated heparin or low molecular weight heparin (>50% drop in platelet counts; arterial or venous thrombosis while the patient is receiving heparin).
Result
antiplatelet factor 4 antibodies may be present
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