Diagnostic value of urinary retinol-binding protein in childhood nephrotic syndrome

Abstract

Urinary excretion of N-acetyl-beta-D-glucosaminidase (NAG) and retinol-binding protein (RBP), sensitive markers of renal tubular damage and dysfunction respectively, were evaluated in paired remission and relapse urine samples from 16 patients (median age 12 years), with minimal change nephrotic syndrome (MCNS), in single samples from 5 nephrotic patients (median age 12 years) with focal segmental glomerulosclerosis (FSGS) and in 183 normal controls aged 2-16 years. The NAG and RBP data were expressed as a ratio over urinary creatinine (Cr). The NAG/Cr and RBP/Cr geometric means (ranges) for normal subjects were 11.1 (3.4-35.5) micromol 2-methoxy-4-(2'-nitrovinyl)-phenol (MNP)/h per mmol and 3.1 (0.3-38.8) microg/mmol, respectively. The NAG/Cr data revealed a weak negative correlation with age in normal children, whereas RBP/Cr was independent of age. RBP/Cr and NAG/Cr in MCNS in remission were the same as in controls. In MCNS in relapse, NAG/Cr was significantly elevated (P=<0.001), while in FSGS both RBP/Cr and NAG/Cr were significantly raised (P=<0.001 and P<0.008, respectively). These findings suggest that elevated NAG/Cr may be an indicator of relapse in both MCNS and FSGS and elevated RBP/Cr may allow differentiation between the two.

Renal tubular dysfunction in children with systemic lupus erythematosus

“…Controls were excluded if autoimmune disease, renal pathology or infection was diagnosed or clinically suspected. The literature has well-established data on tubular function in normal children [19] and those with nephrotic syndrome [18,20] and insulin-dependent diabetes mellitus [21].…”

“…The methods of analysis of patients for both urinary RBP levels and urinary NAG levels were identical to those previously published [18]. The urinary RBP levels were analysed by enzyme-linked immunosorbent assay using rabbit antisera (Dako, High Wycombe, UK) and urinary NAG levels with a commercially available kit (Praill Price Richardson Diagnostics, London, UK) on an IL Monarch centrifugal analyser (Instrumentation Laboratory, Cheshire, UK).…”

“…The data were logarithmically transformed as control RBP and NAG levels are known to be logarithmically distributed [18]. The methods of analysis of patients for both urinary RBP levels and urinary NAG levels were identical to those previously published [18].…”

“…The controls consisted of 94 normal children who were of similar ages [18]. Only urine from these patients was analysed for tubular function for ethical reasons.…”

“…The markers of tubular function were analysed: namely urinary RBP, urinary NAG (Nacetyl-b-d-glucosaminidase) and TRP (tubular reabsorption of inorganic phosphate); and urine amino acids were estimated in all cases. Urine specimens taken from the controls were only analysed for RBP and NAG [18] (as this was the initial control protocol and they would have required blood to be taken for phosphate levels to calculate the TRP). All the urine samples were from the second episode of micturition during the day in order to avoid increased biochemical values found in early morning urine samples [19].…”