Heparin-induced thrombocytopenia (HIT) is a potentially life-threatening condition associated with heparin administration. Many orthopaedic units routinely prescribe low-molecular-weight heparins as thromboprophylaxis after hip and knee arthroplasty.

We postulated that routine platelet monitoring following heparin administration is of no clinical benefit. We therefore asked: firstly, what was the rate of thrombocytopenia in a large population of patients undergoing lower limb arthroplasty? Secondly, did this rate justify routine platelet monitoring?

Unless contraindicated, all patients (n=1999, 53.05% female, mean age 69.23 years) at a UK district general hospital undergoing hip and knee arthroplasty were given daily prophylactic enoxaparin. Platelet counts were obtained between the 8th and 10th postoperative days and compared to preoperative baseline. A > 50% fall in platelet count was classified as “possible HIT”. The minimal acceptable risk of thrombocytopenia was defined using The American College of Chest Physicians (ACCP) 2012 guidelines, which recommend monitoring platelet counts in patients receiving heparin where the expected risk of HIT is>1% and by descriptive cost-benefit analysis based on the cost of routine platelet monitoring in the clinical setting.

Complete results were available for 1361 (68.1%) patients, comprising: 653 primary hips, 22 revision hips, 1 hip resurfacing, 665 primary knees, 19 revision knees and 1 unicompartmental knee replacement. Mean platelet level was 281.9×109/L preoperatively and 527.83×109/L postoperatively. Forty-four patients (3.2%) experienced a postoperative fall in platelet levels. However, no patient experienced a drop in platelets to less than 50% of the preoperative value.

The incidence of HIT in the elective arthroplasty population is low. Therefore, routine postoperative monitoring of platelets is not necessary in this population of patients.

II, prospective study.