Correlation Between Creatinine-Based eGFR and Cystatin C-Based eGFR in Adult Kidney Donor Assessment: A Tertiary Care Center Experience in Saudi Arabia

Background: Accurate estimation of glomerular filtration rate (GFR) is essential in assessing kidney donors. Common methods include nuclear medicine GFR (NM GFR), 24-hour creatinine clearance, and serum-based eGFR. Creatinine eGFR and cystatin C eGFR are widely used due to their convenience. This study evaluates the correlation between these two modalities and their association with age, gender, muscle mass, and body mass index (BMI), and NM GFR as needed. Methods: A retrospective review was conducted on kidney donors evaluated at King Faisal Specialist Hospital and Research Center (KFSHRC), Jeddah, from January 1 to December 31, 2024. Donors were stratified by age (<25, 25–40, >40 years), gender, and BMI (<25, 25–30, >30). Creatinine eGFR was calculated using the Cockcroft–Gault equation, while cystatin C eGFR was derived from the CKD-EPI equation. NM GFR was performed when both estimates were below 90 mL/min/1.73 m BSA. Pearson correlation coefficients assessed eGFR agreement across subgroups. Results: Among 768 donors (52% male, 48% female), the median age was 32 years (IQR: 25–39), and the median BMI was 28.5 kg/m (IQR: 25.7–32.4). In donors <25 years with BMI <25, creatinine and cystatin C eGFR showed strong correlation (r = 0.89, p < 0.001) with a mean difference of 9.8% (95% CI: 8.1–11.4%). However, in those aged 25–40 with BMI >30, creatinine eGFR underestimated renal function by 15–25% compared to cystatin c and NM GFR (r = 0.72, p < 0.01), with a mean absolute difference of 18.2% (95% CI: 15.4–21.0%). In donors >40 years with BMI <30, the difference between creatinine egfr and cystatin c egfr ranged from 11–14%, with cystatin C eGFR aligning more closely with NM GFR (r = 0.81, p < 0.001). NM GFR demonstrated strong alignment with cystatin C eGFR (r = 0.85, p < 0.001), particularly in males aged 25–40 with BMI >30, confirming systematic underestimation by creatinine eGFR in this group. Conclusion: Creatinine eGFR correlates well with cystatin C eGFR in younger donors with lower BMI but significantly diverges in middle-aged males with BMI >30. NM GFR aligns more closely with cystatin C eGFR, highlighting its value in renal assessment. Future studies should validate these findings and refine donor evaluation protocols.