Adjusting Iron Markers for Inflammation Reduces Misclassification of Iron Deficiency After Total Hip Arthroplasty

Background: Preoperative anemia is common among patients undergoing arthroplasty and is associated with increased transfusion requirements and worse outcomes. Current perioperative pathways rely on iron studies to guide intravenous iron supplementation, but systemic inflammation triggered by surgery profoundly alters iron markers, risking misclassification of iron deficiency. This study evaluated whether adjusting iron indices for inflammatory markers improves diagnostic accuracy after total hip arthroplasty (THA). Methods: In this prospective cohort study, 20 patients undergoing elective primary THA at a single center were enrolled. Patients with preoperative inflammation were excluded. Serum iron, transferrin, transferrin saturation (TSAT), CRP, and albumin were measured preoperatively and on postoperative days (PODs) 1, 2, 3, and 90. Serum iron was adjusted for systemic inflammation using a validated regression equation incorporating CRP and albumin, and adjusted TSAT was calculated accordingly. Absolute iron deficiency was defined as serum iron < 10 µmol/L, and functional iron deficiency was defined as TSAT < 20%. Comparisons were made using Wilcoxon's signed-rank test and ANOVA. Results: In the 20 included patients, a pronounced systemic inflammatory response was observed, with CRP peaking on POD 2 (median, 162 mg/L) and albumin falling to 32 g/L on POD 1 (both p < 0.001). Unadjusted serum iron and TSAT fell sharply, with nearly all patients classified as iron-deficient in the first three postoperative days. Adjustment for CRP and albumin significantly attenuated these declines: on POD 2, median iron was 8.2 µmol/L adjusted versus 2.0 µmol/L unadjusted (p < 0.001), and TSAT was 19% versus 4% (p < 0.001). Misclassification of iron deficiency fell by 40-50% with adjustment, and by POD 90, adjusted indices approximated baseline values. Conclusions: Systemic inflammation after THA markedly suppresses iron indices, leading to widespread misclassification of iron deficiency. Adjustment for CRP and albumin reduces this misclassification and provides a more accurate assessment of perioperative iron status. These findings complement existing evidence supporting intravenous iron supplementation by highlighting a diagnostic refinement that could improve patient selection for therapy.