We thank Delanaye and Pottel for their response letter,1 which raises some important points. Our main goal was to assess the relative accuracies of estimated glomerular filtration rate (eGFR) equations based on creatinine, cystatin C, beta-trace protein, and beta-2 microglobulin in hospitalized older adults. We found that the addition of cystatin C to creatinine-based equations improved accuracy, whereas the addition of beta-trace protein and/or beta-2 microglobulin did not. This corroborates earlier literature, but it is one of only a few such studies among elderly multimorbid patients.