C3 and systemic lupus erythematosus: Compared with SLE-S-hypothyroidism group, the average age of SLE-C-hypothyroidism group was older (42.21 ± 14.25 y vs. 36.67 ± 12.94 y, P=0.031), and SLE-C-hypothyroidism group had higher level of ESR (55.02 ± 33.10 mm/h vs. 33.21 ± 31.48 mm/h, P=0.001), creatinine (85.88 ± 86.00 mmol/L vs. 59.41 ± 22.21 mmol/L, P=0.014), 24h urine protein (2.24 ± 3.19 mg/d vs. 0.84 ± 1.44 mg/d, P=0.002) and lower level of C3 (0.63 ± 0.31 g/l vs. 0.78 ± 0.37 g/l, P=0.024), and albumin (29.52 ± 8.24 g/l vs. 36.05 ± 7.05 g/l, P<0.001).