Estimated glomerular filtration rate based on creatinine, cystatin C, β-trace protein and β2 microglobulin in patients undergoing nontraumatic lower extremity amputation.

Creatinine-based estimates were substantially higher than cystatin C-based estimates before amputation and significantly increased across amputation. Estimates combining creatinine and cystatin were stable across amputation, while the addition of BTP and B2M is unlikely to be clinically relevant.