Creatinine-based estimation of rate of long term renal function loss in lung transplant recipients. Which method is preferable?

Background: Progressive renal function loss during long-term follow up is c ommon after lung transplantation and close monitoring is warranted, Since c hanges in creatinine generation and excretion may occur after lung transpla ntation, the reliability of creatinine-based methods of renal function asse ssment to serial measurements of glomerular filtration rate (GFR) were comp ared in this population. Methods: Renal function with serial measurements of GFR by iothalamate clea rance every 6 months after transplantation was studied in a cohort of 40 lu ng transplant recipients with at least 24 months of follow up, transplanted between November 1990 and October 1995 in this center. The correlation bet ween the rate of renal function loss calculated from the slope of GFR and t he following creatinine-based indices: 1/S-creatinine, Cockcroft clearance and Levey estimation were analyzed, The absolute difference between GFR and Cockcroft clearance and Levey estimation pre- post-transplantation at seve ral points was also studied. Results: The slopes of 1/S-creatinine (r = 0.85), Cockcroft clearance (r = 0.86), and the Levey estimation (r = 0.84) correlated significantly with th e slope of GFR as measured by iothalamate clearance. However, all creatinin e-based slopes underestimate the rate of GFR loss. Cockcroft clearance and the reciprocal value of serum creatinine do not detect small GFR losses. Du ring long-term follow up a time-dependent discrepancy between Cockcroft cle arance, Levey estimation and GFR was observed which may partially explain t he observations for this population. Conclusion: Creatinine-based slopes correlate with GFR slopes after lung tr ansplantation, but consistently underestimate the rate of GFR decline. The Levey estimation is the most sensitive method used to detect small GFR loss es and may be preferable when no GFR measurement is available. In special c onditions when an accurate renal function assessment is needed true GFR may be necessary.