535 Are Routine Post-Operative Blood Tests Necessary Following Hip or Knee Arthroplasty in Fit and Well Patients?

Enhanced recovery protocols in hip and knee arthroplasty have achieved same-day discharge in selected patients. However, abnormal serum sodium, haemoglobin and creatinine may affect postoperative management. In particular, Serum creatinine guides dosage of prophylactic direct oral anticoagulants (DOAC). In this study we aim to establish if post-operative blood tests following arthroplasty might affect management. Method Patients undergoing primary hip and knee arthroplasty surgery at our unit between April 2018 and March 2019 were included. National Joint Registry input forms were used to identify the patients and their American Society for Anaesthesiologists (ASA) grade. Patients with an ASA grade of 1 or 2 were included. The incidence of AKI, hyponatraemia, drop in haemoglobin below 80g/L (the threshold for consideration of transfusion) and altered DOAC dose were recorded. For statistical analysis, the z-test of single proportion was used to compare results to a hypothesised expected population proportion of 1% for group sizes greater than 10. The p-value was set to 0.05. Results Results leading to a change in management were seen in 19 of the 218 patients (8.7%) (p < 0.0001). Twelve patients (5.5%) developed stage 1 or 2 AKI (p < 0.0001). Three patients required a reduction in the DOAC dose in response to their post-operative creatinine result. Post-operative haemoglobin level was below 80 g/L in two patients. Hyponatraemia was observed in one fifth of the patients and required intervention in two patients. Conclusions Post-operative blood tests are essential prior to discharge for all patients following hip and knee arthroplasty, regardless of pre-operative status.