Clinical significance of fractional magnesium excretion (FEMg) as a predictor of interstitial nephropathy and its correlation with conventional parameters

Background Elevated urine Mg excretion and its correlation with histological damage in tubulo-interstitial nephropathy (TIN) were reported. Here we investigated the clinical significance of the fractional excretion of Mg (FEMg) for the prediction of TIN. Methods We enrolled and assessed 94 adult patients with various renal diseases diagnosed principally by renal biopsy. Results Our stratified analysis based on the value of the conventional TIN parameter N -acetylglucosaminidase (NAG) excretion showed that the high-NAG index group (more than median value of NAG-to-Cr ratio, n = 47) demonstrated significantly high FEMg values ( p = 0.017). A univariate analysis revealed a significant correlation between the FEMg and the NAG index ( R = 0.60) but not for other parameters. A multivariate regression analysis confirmed the significance of the FEMg as an effective predictor of the NAG index. The FEMg showed a significant correlation with the estimated glomerular filtration rate (eGFR) in the patients with eGFR ≤ 30 mL/min. The correlation of FEMg with the NAG index was not observed in the primary glomerulonephritis patients but was apparent in the patients with hypertensive nephrosclerosis or interstitial nephritis. Conclusion Our findings may indicate that the combination of the FEMg and the NAG index can provide a specific, sensitive assessment for TIN in patients without renal insufficiency.