Fractional excretion of protein may be a useful predictor of decline of renal function in pan-chronic kidney diseases.

Fractional excretion of protein may be a useful predictor of decline of renal function in pan-chronic kidney diseases Sir, We agreed with the article of McQuarrie article 'Fractional excretions of albumin and IgG are the best predictors of progression in primary glomerulonephritis'. But we were curious about the glomerular filtration rate (GFR) of high-and low-risk group patients separated by fractional excretion of albumin (FEalbumin), because firstly FEalbumin, which was albumin clearance divided by creatinine clearance (Ccr), seemed associated with Ccr as well as albuminuria, and secondly advanced decreased GFR [1] as well as pro-teinuria or albuminuria [1, 2] had been reported as the pre-dictor of progression of chronic kidney disease (CKD). We examined the relationships among fractional excre-tion of protein (FEprotein), urinary protein excretion rate (ProteinEx) and Ccr in 179 adult patients with CKD of various origins whose Ccr values were between 15 and 89 mL/min/1.73m 2 (CKD Stages II, III and IV). The scatter plot, even though showing a linear relationship between ProteinEx and FEprotein (r = 0.830, P < 0.001), looked fan shaped, and while ProteinEx diviated from 0, the association between ProteinEx and FEprotein decreased (Figure 1A). We drew the same scatter plot between ProteinEx and FEprotein again displaying each pa-tient's stage of CKD. Each group of the three CKD stages was clearly separated and the slope was increased as the stage increased. This suggested that patients with higher FEprotein values in the same level of ProteinEx would be in the more advanced stage of CKD (Figure 1B). FEalbumin is similar in both fractional excretion (FE) of sodium and selectivity index (SI) of protein in the formula structure but these results are interpreted differently. FEal-bumin does not indicate the tubular function because albu-min, unlike sodium in FE of sodium, is not filtered in the glomerulus. It also does not indicate permselectivity of the glomerulus because creatinine, unlike albumin or transfer-rin in the SI of protein, is fully filtered in glomerulus. We thought that the reason FEalbumin was a better pre-dictor of progression in primary glomerulonephritis than urinary albumin excretion rate or albumin-to-creatinine ratio was not because it was a more accurate indicator of the impairment of glomerular permselectivity as the authors speculated, but rather because it was a more sensitive formula containing decreased filtration function of the glom-erulus with increased glomerular albumin permeability. In conclusion, although this experiment was performed using total protein in patients with CKD …