Because direct measurement of GFR is cumbersome, it is often estimated using serum creatinine clearance. Problem is, most folks must lose more than 50% of their kidney function before the SCr measures above normal. The goal, of course, of eGFR is to produce results as close to mGFR as possible.
So – the authors compared estimated GFR with measured GFR in 508 consecutive living kidney donors.
“The level of agreement between mGFR [measured GFR] and all three eGFR [estimated GFR] values was poor…We conclude that reliance on creatinine-based eGFR values is unsatisfactory for the evaluation of potential living kidney donors.”
According to MedLine from the National Institute of Health, “measuring” GFR involves a blood test. Over here it talks about a catheter to ensure collection of all urine. OPTN’s policy on the medical evaluation of living kidney donor requires “Measurement of glomerular filtration rate by isotopic methods or a creatinine clearance calculated from a 24-hour urine collection”. To me, that sounds more like eGFR than mGFR (Neither of those methods involve blood). Disconcerting if true.
Admittedly, much of this can be confusing to a non-medical person (myself included). If you’re interested in reading further about ways to measure GFR, this might be a place to start: http://cdn.intechopen.com/pdfs-wm/29474.pdf
Bhuvanakrishna, T., Blake, G., Hilton, R., Burnapp, L., Sibley-Allen, C., & Goldsmith, D. (2014). Comparison of estimated GFR and measured GFR in prospective living kidney donors International Urology and Nephrology DOI: 10.1007/s11255-014-0859-y