Elsevier

Kidney International

Volume 57, Issue 1, January 2000, Pages 240-249
Kidney International

Clinical Nephrology – Epidemiology – Clinical Trials
Tubular proteinuria defined by a study of Dent's (CLCN5 mutation) and other tubular diseases

https://doi.org/10.1046/j.1523-1755.2000.00847.xGet rights and content
Under an Elsevier user license
open archive

Tubular proteinuria defined by a study of Dent's (CLCN5 mutation) and other tubular diseases.

Background

The term “tubular proteinuria” is often used interchangeably with “low molecular weight proteinuria” (LMWP), although the former implies a definite etiology. A specific quantitative definition of tubular proteinuria is needed, and we address this by studying five different renal disorders.

Methods

Tubular proteinuria was assessed by measuring urinary retinol-binding protein (RBP), β;2-microglobulin (β;2M), α1-microglobulin (α1M), and albumin in 138 patients: 26 affected males and 24 female carriers of the X-linked syndrome “Dent's disease,” 6 patients with other Fanconi syndromes, 17 with distal renal tubular acidosis (dRTA), 39 with glomerulonephritis (GN), and 26 with Chinese herbs nephropathy (CHN).

Results

RBP was better than β;2M or α1M in identifying the tubular proteinuria of Dent's disease. Median urinary RBP levels in mg/mmol creatinine were: affected male Dent's, 18.2, N = 26; carrier female Dent's, 0.30, N = 24; dRTA, 0.027, N = 17; GN, 0.077, N = 39; and normal adults, 0.0079, N = 61. Elevated urinary RBP (>0.017) and albumin < (10 × RBP) + 2 identified all patients with the LMWP of Dent's disease and clearly distinguished their LMWP from that of dRTA and GN. This is a quantitative definition of tubular proteinuria. Consistent with this definition, 80% of those patients with CHN who had an elevated RBP had tubular proteinuria. Urinary RBP and albumin in carriers of Dent's disease were strikingly correlated over a 100-fold range (R = 0.933).

Conclusion

The combination of elevated urinary RBP (>0.017) and albumin < (10 × RBP) + 2 (mg protein/mmol creatinine) is a quantitative definition of tubular proteinuria. Furthermore, our findings suggest that a shared defect in tubular RBP and albumin reuptake causes this form of proteinuria.

Keywords

low molecular weight proteinuria
Dent's disease
retinol binding protein
albumin
urine proteins
proximal renal tubular disease

Cited by (0)