Routine post-operative bloods following all elective arthroplasty may be unnecessary. This retrospective cohort study aims to define the proportion of post-operative tests altering clinical management.

Clinical coding identified all elective hip or knee joint replacement under Hawkes Bay District Health Board contract between September 2019-December 2020 (N=373). Uni-compartmental and bilateral replacements, procedures performed for cancer, and those with insufficient data were excluded. Demographics, perioperative technique, and medical complication data was collected. Pre- and post-operative blood tests were assessed. Outcome measures included clinical intervention for abnormal post-operative sodium (Na), creatinine (Cr), haemoglobin (Hb), or potassium (K) levels. A cost-benefit analysis assessed unnecessary testing.

350 patients were Included. Median age was 71 (range 34-92), with 46.9% male. Only 26 abnormal post-operative results required intervention (7.1%). 11 interventions were for low Na, 4 for low K, and 4 for elevated Cr. Only 7 patients were transfused blood products. Older age (p=0.009) and higher ASA (p=0.02) were associated with intervention of any kind. Abnormal preoperative results significantly predicted intervention for Na (p<0.05) and Cr (p<0.05). All patients requiring treatment for K used diuretic medication. Preoperative Hb level was not associated with need for transfusion. Overall, there were 1027 unnecessary investigations resulting in $18,307 excess expenditure.

Our study identified that the majority of elective arthroplasty patients do not require routine postoperative blood testing. We recommend investigations for patients with preoperative electrolyte abnormality, those taking diuretics, and patients with significant blood loss noted intra-operatively. In future, a larger, randomised controlled trial would be useful to confirm these factors.