Mitochondrial DNA damage in the renal proxmimal tubual has been attributed to toxic drugs such as tenofovir. Sudden catastrophic renal failure has been documented. A reliable indicator of kidney health will be able to detect such damage as well as renal eithelial cancers.
In 1995 Jacobsson, Lignelid and Bergerheim reported:
"Transthyretin and cystatin C are catabolized in proximal tubular epithelial cells and the proteins are not useful as markers for renal cell carcinomas"
https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2559.1995.tb00275.x