- 1) Known hypersensitivity to contrast media 2) Patients taking Metformin 3) Serum creatinine above 180Fmol/L 4) Platelets &lt; 100 x 10 9/L, INR/PTT &gt; 1.5 x normal 5) History of heparin induced thrombocytopenia 6) Allergy to heparin or fish 7) Prior use of protamine sulfate (i.e., protamine-containing insulin) 8) Vasectomized or infertile males 9) History of bleeding disorder 10) Bilateral total knee arthroplasty 11) History of stroke or myocardial infarction in previous 6 months 12) Traumatic spinal anaesthesia (two or more attempts and/or bloody) 13) History of previous DVT/PE 14) Active peptic ulcer disease (e.g., GI bleed, rectal bleed) 15) Currently on chronic anticoagulant therapy 16) Contra-indication to heparin 17) Patient is taking part in any other investigational study 18) Previous contralateral TKR or hip replacement