A transparent lens on estimated GFR
May 2021—Forget about who’s buried in Grant’s Tomb (though for the record it’s Grant, his wife, and their dog). For laboratories, the deceptively simple question now under scrutiny is, What is estimated GFR? It is indeed an estimate, for starters—an approximation of glomerular filtration rate, which in turn is a physiological parameter that’s actually difficult to measure, says Greg Miller, PhD. Even so-called measured GFR values are not very precise in individual patients. It’s been carried along by several equations over the decades: Cockcroft-Gault, MDRD, and CKD-EPI, all of which (to the consternation of some) are still in use. It guides clinical care, including referrals to specialists and placement on kidney transplant lists, as well as dosing of medications such as metformin. Some call it a workhorse. But estimated GFR (eGFR) has also long been saddled with a race-based component, a coefficient that adjusts for better kidney function for Black patients compared with other patients.