Early tubular proteinuria and the development of nephritis in Henoch-Schönlein purpura

Abstract 

The prognosis of Henoch-Schönlein purpura (HSP) is mainly determined by the involvement of the kidney, but prognostic markers have not been established. To study the extent of tubular involvement in HSP and its relationship to the development of HSP nephritis, we measured the urinary excretion of two tubular marker proteins in 36 children with HSP. After admission, urinary N-acetyl-β-D-glucosaminidase (NAG) was determined in 20 children and α₁-microglobulin (α₁-MG) in 16 children respectively. These values were compared with the biochemical data on admission, 1 month, 6 months, and 12 months later. A total of 198 24-h urine samples from healthy children were used for the establishment of reference data for NAG and α₁-MG (mean±2 SD). Twenty-one patients had elevated excretion of either NAG (>mean+2 SD, n=12) or α₁-MG (>mean+2 SD, n=9). The highest values (>mean+4 SD) were found in patients with early kidney involvement. Normal values were accompanied by a benign further clinical course. Children with intermediate high values (>mean+2 SD, <mean+4 SD) developed signs of renal involvement during follow-up. Hence, tubular proteinuria is common during the early stages of HSP. NAG and α₁-MG levels correlate well with the extent of early and late renal involvement. Tubular marker proteins may be prognostic markers for the development of HSP nephritis.