Association of Functional and Absolute Iron Deficiency with C-Reactive Protein in Chronic Kidney Disease Patients with Anemia

Abstract

Background: Chronic kidney disease (CKD) patients with anemia often experience iron deficiency, which can be classified as functional or absolute, complicating management strategies. Inflammation, marked by elevated C-reactive protein (CRP) levels, plays a crucial role in functional iron deficiency by altering iron metabolism and availability.

Objectives: To determine the occurrence of functional (FID) and absolute iron deficiency (AID) in CKD patients with anemia and their association with CRP levels.

Methods: This was a comparative, analytical cross-sectional study conducted in the Department of General Medicine and Nephrology among CKD patients between July 2023 and December 2024. Haemoglobin levels were measured, and patients classified into functional or absolute iron deficiency based on transferrin saturation (TSAT) and ferritin levels, and CRP levels measured in both groups. Analysis was done using Stata v16.

Results: Among the 100 participants, 85% had TSAT levels below 20%, with 58.8% classified as having FID and 41.2% as having AID. Haemoglobin levels were comparable between the groups (8.3 g/dL vs. 8.2 g/dL, p = 0.759). Serum creatinine and blood urea levels showed no significant differences between the groups. However, serum ferritin levels were significantly higher in the functional iron deficiency group (144.4 ng/dL vs. 20.7 ng/dL, p < 0.001), while serum iron, TIBC, and TSAT were similar. CRP levels were significantly elevated in the FID group (50.8 mg/L vs. 34.6 mg/L, p = 0.010), indicating a stronger inflammatory response. CRP levels showed a significant negative correlation with haemoglobin (r = -0.341, p = 0.001) and a positive correlation with ferritin (r = 0.288, p = 0.004), suggesting an inflammatory influence on iron metabolism. ROC analysis demonstrated that CRP >41.0 mg/L had moderate discriminatory power for predicting FID (AUC = 0.663, p = 0.011).

Conclusion: This study highlights the significant role of inflammation in functional iron deficiency among CKD patients with anemia, as evidenced by elevated CRP levels and their association with ferritin and haemoglobin.