# Postoperative inflammatory markers are not associated with hidden blood loss after knee arthroscopy

## TL;DR

This study found that increased inflammation after knee surgery does not mean more hidden blood loss.

## Contribution

The study shows that postoperative inflammation and hidden blood loss are not linked, challenging previous assumptions.

## Key findings

- Postoperative CRP and WBC levels increased significantly after knee arthroscopy.
- No significant association was found between inflammatory markers and hidden blood loss.
- Hidden blood loss and inflammation appear to be separate physiological processes.

## Abstract

Hidden blood loss (HBL) and systemic inflammatory response are common after knee arthroscopy, but whether they are interrelated remains unclear. This study aimed to investigate if changes in inflammatory markers (∆CRP and ∆WBC) are associated with HBL, independent of known hematological predictors.

A total of 34 patients undergoing knee arthroscopy were included. Demographic, surgical, and laboratory data were collected. HBL was calculated using a standard formula. Inflammatory markers (CRP and WBC) were measured preoperatively and postoperatively. Linear regression was used to assess the association between HBL and ∆CRP/∆WBC, adjusting for covariates.

A total of 34 patients were included. Postoperatively, the median CRP was 5.36 mg/L (IQR 2.80–12.20), the mean WBC was 9.25 ± 2.07 × 109/L, and the median HBL was 393.60 mL (IQR 273.42–672.97). Postoperative CRP and WBC levels increased significantly compared to preoperative values (p < 0.001). However, neither univariate nor multivariate analysis showed a significant association between ∆CRP or ∆WBC and HBL (p > 0.05).

Although inflammatory markers increased significantly after knee arthroscopy, they were not associated with HBL. This suggests that postoperative inflammation and hidden blood loss represent distinct pathophysiological processes. Clinicians should understand that while postoperative fever and elevated inflammatory markers are expected, they do not indicate increased blood loss, and HBL itself is not a risk factor for infection.