Low-grade proteinuria and microalbuminuria in renal transplantation.

Nephrotic-range proteinuria has been known for years to be associated with poor renal outcome. Newer evidence indicates that early (1-3 months after transplantation) low-grade proteinuria and microalbuminuria (1) provide information on the graft in terms of donor characteristics and ischemia/reperfusion injury, (2) may occur before the development of donor-specific antibodies, (3) predict the development of diabetes and cardiovascular events, and (4) are associated with reduced long-term graft and patient survivals. Low-grade proteinuria and microalbuminuria are also predictive of diabetes, cardiovascular morbidity, and death in nontransplanted populations, which may help us to understand the pathophysiology of low-grade proteinuria or microalbuminuria in renal transplantation. The impact of immunosuppressive medications, including mammalian target of rapamycin inhibitors, on graft survival is still discussed, and the effect on proteinuria is crucial to the debate. The fact that chronic allograft rejection may exist as early as 3 months after renal transplantation indicates that optimal management of low-grade proteinuria or microalbuminuria should occur very early after transplantation to improve long-term renal function and the overall outcome of renal transplant recipients. The presence of low-grade proteinuria or microalbuminuria early after transplantation must be taken into account to choose adequate immunosuppressive and antihypertensive medications. Limited information exists regarding the benefit of therapeutic interventions to reduce low-grade proteinuria or microalbuminuria. Whether renin angiotensin blockade results in optimal nephroprotection in patients with low-grade proteinuria or microalbuminuria is not proven, especially in the absence of chronic allograft nephropathy. Observational studies and randomized clinical trials yield conflicting results. Finally, randomized clinical trials are urgently needed.