TPO and lupus nephritis: SLE: systemic lupus erythematosus; AbTPO: anti-thyroid peroxidase antibodies; TSH: thyroid-stimulating hormone; T4: thyroxine; T3: triiodothyronine; AITD: autoimmune thyroid disease; ICD-9: International Classification of Diseases, Ninth Revision; ACR: American College of Rheumatology; LN: lupus nephritis; GFR: glomerular filtration rate; SELENA-SLEDAI: Safety of Estrogens in Lupus Erythematosus National Assessment-Systemic Lupus Erythematosus Disease Activity Index