The race-independent glomerular filtration rate (GFR) estimating equation with creatinine, cystatin C, β-trace protein (BTP), and β2-microglubulin (B2M) proposed by Inker et al1 as a replacement for creatinine-based equations is neither optimal nor cost-effective. In a recent study of 2,893 plasma proteins, 680 correlated with measured GFR (mGFR), with cystatin C showing the highest correlation, while B2M was not among the 8 best.2 The results by Inker et al show that the improvement of 1 – P30, when using the recommended cystatin C-B2M-BTP equation (1 – P30=15.6), rather than the one based only upon cystatin C (1 – P30=17.4), is not clinically significant and the lack of international calibrators for B2M and BTP will make it very difficult to reproduce this possible advantage in clinical practice.