Re-evaluating the utility of routine postoperative laboratory tests after primary total knee arthroplasty.

Background: While advancements in surgery and reduced complication rates have made total knee arthroplasty (TKA) one of the most successful and cost-effective procedures in orthopaedic surgery, routine postoperative laboratory tests are still being ordered without evidence as to their necessity. With expansion of the bundled payment models, there may exist an opportunity to cut overall costs while maintaining quality of care by eliminating unnecessary interventions. The objective of this study was to examine the utility of routine postoperative laboratory tests in TKA.

Methods: A retrospective review of 319 TKAs performed at a single institution over a 2-year period was performed. The primary outcomes were the rates of acute blood loss anemia requiring transfusion, acute kidney injury (AKI), electrolyte abnormalities, and 90-day emergency department visits and readmissions. Multivariate logistic regression analysis was also performed to identify the risk factors associated with abnormal laboratory values.

Results: 89 patients (27.9%) had abnormal postoperative laboratory results, of which 78% were exclusively due to electrolyte (sodium or potassium) abnormalities. The rates of AKI and blood transfusion were 3.8% and 1% respectively. Factors associated with electrolyte abnormalities were abnormal baseline electrolyte levels (p = 0.002 and = 0.006 for sodium and potassium respectively) and anemia (p = 0.049). Factors associated with blood transfusion were ASA score ≥3, preoperative anemia, and no tranexamic acid use. Factors associated with AKI were chronic kidney disease or having at least two of the following: age >65 years, BMI> 35, ASA score ≥3, diabetes, heart disease, and/or anemia. Laboratory results did not change the course of care in 305 of 319 patients (95.6%). There was no increased risk for 90-days ED visits or readmissions with abnormal laboratory values (p = 0.356).

Conclusion: With increasing pressure for cost containment in an era of bundled payment models, the very low rate of laboratory associated interventions suggest that routine postoperative laboratory tests is not justified. Obtaining laboratory after primary, unilateral TKA should be driven by patients' risk factors.