# Relevance of Routine Postoperative Biochemical Tests in Primary Hip and Knee Arthroplasty Patients: Assessing Necessity and Clinical Outcomes

## TL;DR

This study finds that routine blood tests after hip and knee surgery often don't lead to important actions and may delay patient discharge.

## Contribution

The study introduces a risk-based approach to selectively perform postoperative blood tests, potentially reducing unnecessary procedures.

## Key findings

- Most patients had normal postoperative lab results, with few requiring interventions.
- Routine blood tests led to discharge delays in over half of cases.
- A selective testing strategy based on preoperative risk factors could be safe and efficient.

## Abstract

Introduction

Routine postoperative blood tests are common after primary hip and knee arthroplasty, but their value for every patient is uncertain in the era of enhanced recovery and routine transexamic acid. In the context of the United Kingdom (UK), this study sought to evaluate the clinical utility of next-day laboratory testing and to identify preoperative features that might permit selective testing.

Methods

A retrospective audit was performed in 99 consecutive primary total hip (n=51) and knee (n=48) arthroplasties undertaken at a tertiary centre. Demographic and laboratory data (pre- and post-operative haemoglobin, white cell count, platelets, electrolytes and creatinine/estimated glomerular filtration rate (eGFR)) were collected. Normality was assessed, and paired comparisons used a paired t-test or Wilcoxon signed-rank test as appropriate. Outcomes included blood transfusion, and other interventions prompted by test results, delays to discharge and readmissions. Statistical significance was set at p<0.05, and 95% confidence intervals were reported for mean differences.

Results

The cohort had a mean age of 69.5±10.1 years and comprised 50 men and 49 women. Mean haemoglobin fell from 136.33±12.83 g/L preoperatively to 115.81±13.03 g/L postoperatively. Mean haemoglobin change is 20.52 g/L (paired t=18.59; p<0.001), showing a statistically significant fall in haemoglobin after surgery. Mean white cell count rose and mean platelet count fell, consistent with an expected postoperative response. A total of 93 (93.9%) patients had normal renal indices, and 91 (91.9%) had normal electrolytes postoperatively. Moreover, nine patients (9.1%) were readmitted for clinical issues (wound problems, limb swelling or suspected venous thromboembolism (VTE) , infection or falls). No patient required blood transfusion. A total of 57 discharges (51.4%) were delayed while awaiting laboratory results.

Conclusion

Routine next-day blood tests after uncomplicated primary lower-limb arthroplasty produced predictable but infrequently actionable abnormalities and contributed to discharge delays. A selective, risk-based approach, directed at patients with low preoperative haemoglobin, impaired renal function, electrolyte derangement or other clinical concerns, appears safe and may reduce unnecessary testing, costs and length of stay.