Iron Deficiency and Renal Phosphate Handling: The Role of Maximal Tubular Reabsorption of Phosphate Normalized to Glomerular Filtration Rate (TmP/GFR) in Proximal Tubular Dysfunction.

BACKGROUND AND AIM: Phosphate dysregulation is often associated with chronic kidney disease (CKD), and recent studies suggest that it may also be present in non-CKD patients with systemic conditions including iron deficiency anemia. This study aimed to evaluate the relationship between iron deficiency parameters (total iron-binding capacity {TIBC}, hemoglobin, and serum ferritin) and markers of proximal tubular dysfunction (the maximal tubular reabsorption of phosphate normalized to glomerular filtration rate {TmP/GFR} and tubular reabsorption of phosphate {TRP}) in non-CKD patients with iron deficiency anemia.

METHODS

This was a hospital-based analytical cross-sectional study conducted in the outpatient department and/or inpatient wards of the Department of Internal Medicine, Swaroop Rani Nehru (SRN) Hospital associated with Moti Lal Nehru (MLN) Medical College, Prayagraj, Uttar Pradesh, India, between July 2023 and August 2024.

RESULTS

This study analyzed 40 anemic patients without CKD, with a mean age of 33.9 years. Most participants (n=24, 60%) were aged 18-35 years, and the majority (n=27, 67.5%) were female. Peripheral smear analysis revealed that 72.5% (n=29) had microcytic hypochromic anemia. Hemoglobin levels averaged 7.7 g/dL, serum iron was 91.0 µg/dL, total iron-binding capacity (TIBC) was 316.3 µg/dL, and serum ferritin was 199.7 ng/mL. Phosphate handling was assessed with TmP/GFR and tubular reabsorption of phosphate (TRP) showing mean values of 4.1 mg/dL and 99.2%, respectively. This study found that TmP/GFR had a significant positive correlation with TIBC (r=0.402, p=0.010), but non-significant negative correlations with hemoglobin and serum iron. TRP was negatively correlated with hemoglobin and serum ferritin, but not significantly. Among patients with microcytic hypochromic anemia, 55.2% (n=16) had increased TmP/GFR, and 61.1% (n=20) of patients with iron deficiency anemia exhibited increased TmP/GFR. Regression analysis revealed that TIBC significantly predicted TmP/GFR (p=0.022), indicating that higher TIBC values are associated with increased TmP/GFR, suggesting a potential link between iron metabolism and renal phosphate handling.

CONCLUSION

Higher TIBC levels were associated with increased TmP/GFR, suggesting that iron deficiency anemia may influence proximal tubular function. The findings emphasize the importance of considering renal phosphate handling in patients with iron deficiency anemia.