Relationship between the levels of uTWEAK and clinical and histopathologic characteristics in patients with IgAN. The levels uTWEAK at the time of renal biopsy in 116 IgAN patients showed significantly correlations with: (A) urinary protein excretion, r = 0.54, P < 0.001; and (B) extracapillary proliferation, r = 0.32, P < 0.001. (C) There was no significant association between the levels of serum TWEAK (sTWEAK) and uTWEAK (r = 0.05, P = 0.65). (D) Box plots of the levels of uTWEAK with different histological grades in patients with IgAN. The level of uTWEAK in Grade III + IV (n = 12, median: 145.7, IQR 97.5-195.6 pg/mgCr) was significantly higher than those in Grade I (n = 63, median: 78.6, IQR 52.3-115.7 pg/mgCr; **P < 0.001) or Grade II (n = 41, median: 103.7, IQR 70.9–162.5 pg/mgCr; *P < 0.05). The lines in the box plots and the error bars are median and 10–90 percentiles.