Extensive evidence suggests that normal measured glomerular filtration rate (mGFR) indexed for body surface area (BSA) may be slightly lower in young and middle-aged women than men.1-3 A recent substudy of a US community-based older cohort, Multi-Ethnic Study of Atherosclerosis (MESA-Kidney), reported a 12% lower mGFR in women than men.4 This difference was not observed in a prior substudy of an Icelandic community-based older cohort, Aging Genes Environment Susceptibility (AGES-Kidney), using similar methods for GFR measurement.