Clinically important HIT is rare with LMWH except in patients receiving the drug in some post-operative settings. Evidence suggests the risk of developing HIT with LMWH is greatest in patients who have undergone cardiac surgery, and that other patients do not require monitoring. The most common type of HIT is immune-mediated and does not normally develop until 5-10 days after starting unless the patient has been exposed to heparin in the previous 100 days. Prior to commencing heparin or LMWH a baseline platelet count should be checked.

Post-operative patients including obstetric cases receiving UFH should have platelet count monitoring performed daily from days 4-14 or until UFH is stopped.

Post-cardiopulmonary bypass patients receiving LMWH should have platelet count monitoring performed daily from days 4-14 (if an in-patient) or until LMWH is stopped. If an outpatient, then FBC checks every 2-3 days is advised until day 14 post-operatively.

Post-operative patients (other than cardiopulmonary bypass patients) receiving LMWH do not need routine platelet monitoring.

All post-operative patients including cardiopulmonary bypass patients who have been exposed to heparin in the previous 100 days and are receiving any type of heparin should have a platelet count determined 24 hours after starting heparin.

Orthopaedic, surgical and gynaecology patients discharged on LMWH should be advised of the small risk of HIT, and advised that in the event of general malaise, development of signs and symptoms of venous thrombosis, and development of erythematous or necrotic areas at the site of injection, they should have an urgent FBC check to ensure there has not been a 30% fall in the platelet count from the pre-operative baseline.

If HIT is strongly suspected or confirmed, dalteparin should be stopped and an alternative anticoagulant such as fondaparinux, argatroban or danaparoid should be given.