Objective  To explore the association of urinary heme oxygenase 1 （HO-1） with renal damage and lupus activity in patients with systemic lupus erythematosus （SLE） and determine the value of urinary HO-1 in the diagnosis and activity estimation of lupus nephritis （LN）.

Methods  A total of 65 patients with confirmed SLE were assigned into two groups of LN （n = 40） and non-LN （n = 25） according to whether or not there was renal damage. Urinary HO-1 was measured by enzyme-linked immunosorbent assay （ELISA） while the level of disease activity assessed by SLE Disease Activity Score （SLEDAI）. Urinary HO-1 level and other clinical data were compared between two groups. Logistic regression was utilized for examining the risk factors of LN and receiver operating characteristic （ROC） curve plotted for determining the diagnostic efficacy of urinary HO-1 for renal damage.

Results  Urinary HO-1 level in patients with renal damage was significantly higher than that without renal damage （740.42 ± 86.98）ng/L vs （679.03 ± 61.33）ng/L, P = 0.003. Urinary HO-1 level was correlated positively with SLEDAI, serum creatinine and urinary protein while negatively with glomerular filtration rate and creatinine clearance rate. Urinary HO-1, IgG, hypocomplementemia and hematuria were independent risk factors for LN （AUC = 0.853,95%CI: 0.753-0.953）. Area under the ROC curve for HO-1 alone was 0.710. When HO-1 was 721 ng/L, Youden index reached the optimal cut-off value.

Conclusion  Urine HO-1 level is significantly elevated in SLE patients with renal damage and it is associated with lupus activity. And HO-1 has clinical value in determining renal damage and disease activity in SLE patients.