Re-evaluating the Need of Postoperative Blood Testing in Low-Risk Patients After Primary Elective Arthroplasty: A Single-Centre Retrospective Analysis.

Introduction Increasing demand and financial burdens are placing significant strain on current health resources. To help ease pressures, there has been increased emphasis on improving patient flow and saving costs within the health service. Routine postoperative blood tests in otherwise healthy patients may add to delays and healthcare costs without influencing subsequent management. Recent studies suggest that routine postoperative blood tests may be unnecessary in fit and healthy patients undergoing elective arthroplasty. We aimed to assess this practice at our institution in the American Society of Anaesthesiologists (ASA) grade 1 and 2 patients undergoing elective hip and knee arthroplasty. Methods We conducted a retrospective review of 1595 consecutive elective hip and knee replacements in ASA 1 and ASA 2 patients at our institution over a one-year period from 2021 to 2022. Operation notes and electronic databases were analyzed to collect data regarding demographics, co-morbidities, treatment, pre and postoperative blood tests, and any documented interventions in these patients. Binomial logistic regression was employed to identify risk factors associated with postoperative abnormalities and the need for clinical intervention.  Results Postoperative blood abnormalities were identified in 75.4% of patients, primarily anaemia (69.2%) and hyponatremia (29.9%). Anaemia was similarly prevalent in both total hip arthroplasty (THA) and total knee arthroplasty (TKA) patients, with 70.2% affected in each group, although the majority of cases were mild (83.8% in THA and 90.5% in TKA). Hyponatremia was significantly more common in TKA patients (40.3%) compared to THA patients (19.3%), although most cases were mild in severity. Only 5% of cases required any intervention, with higher rates observed in the TKA group compared to the THA group (p=0.008). Blood transfusion rates were low, occurring in 0.6% of cases. Factors associated with postoperative anaemia included higher BMI, preoperative antiplatelet use, and lower preoperative haemoglobin levels, while postoperative hyponatremia was linked to preoperative sodium levels, loop diuretic use, and PPI use. Acute Kidney Injury (AKI) was identified in 2.2% of patients and was predominantly mild. Potassium abnormalities were infrequent, with hypokalemia occurring in 1.5% of patients and no cases of hyperkalemia in our series. Conclusions Although postoperative blood test abnormalities were common, the majority were mild and rarely influenced management in this low-risk cohort of patients, with overall low postoperative intervention rates. Selective blood testing may allow safe targeted testing in this low-risk cohort of patients, minimizing costs and saving valuable resources.