Renal reserve test: its methodology and significance.

Renal reserve (RR) is the ability of the kidneys to increase their basal glomerular filtration rate (GFR) by at least 20% after a protein overload. It has been documented that RR is preserved in healthy elderly people, and even in patients with chronic kidney disease, but its magnitude is significantly decreased with aging. Besides, RR has also been evaluated in kidney transplant patients who were on sirolimus or calcineurin inhibitors (CNI):cyclosporine or tacrolimus, and it was found that RR was lower in the CNI group compared to the sirolimus group, a phenomenon that could be attributed to the intra- renal vasoconstrictive effect of CNI. In conclusion, RR is a physiological variable which has its particular characteristics in different renal settings.