Complement degradation product C3d in urine: marker of lupus nephritis.
OBJECTIVE
To examine whether serum and urine C3d, a degradation product of C3, correlate with renal and extrarenal lupus activity.


METHODS
Serum and urinary C3d levels were measured by ELISA in 15 healthy individuals and 24 patients with systemic lupus erythematosus (SLE) (8 with inactive disease, 7 with active but nonrenal disease, 9 with active lupus nephritis). Disease activity variables like serum C3, C4, and anti-dsDNA antibodies were also measured.


RESULTS
The median serum C3d levels were significantly higher (p < 0.01) in patients with active (26 arbitrary units/ml; AU/ml) and inactive SLE (27 AU/ml) compared to healthy controls (11.25 AU/ml); levels were comparable in patients with active renal and extrarenal SLE. On the other hand, urine C3d was elevated only in patients with active SLE; its level was highest in patients with active lupus nephritis (0.87 AU/ml) compared to patients with active extrarenal diseases (0.31 AU/ml; p < 0.05), to patients with inactive lupus nephritis (0.06 AU/ml; p < 0.001), or to levels in healthy individuals (0.06; p < 0.001). Urine C3d showed stronger correlation with disease activity score (SLE Disease Activity Index) than serum C3, C4, anti-dsDNA antibodies, and serum C3d.


CONCLUSIONS
Urine C3d is a good index of active lupus, particularly lupus nephritis.
Negi
V S
VS
Department of Clinical Immunology, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, India.
Aggarwal
A
A
Dayal
R
R
Naik
S
S
Misra
R
R
D000293:Adolescent; D000328:Adult; D015415:Biomarkers; D002648:Child; D015933:Complement C3d / Q000652:urine*; D005260:Female; D006801:Humans; D008180:Lupus Erythematosus, Systemic / Q000652:urine; D008181:Lupus Nephritis / Q000652:urine*; D008297:Male
D015415:Biomarkers; D015933:Complement C3d