**2. Renal biopsy**

The renal biopsy is the gold standard for the diagnosis of LN, providing important information to the clinician for the management of the patients [7–9]. A diagnosis of SLE is based on clinical systemic features and serologic tests attending the American College of Rheumatology (ACR) criteria for SLE [10]. However, it is not uncommon that the renal biopsy shows morphologic expressions that is very suspicious or conclusive of LN before extrarenal manifestations are evident [11]. The renal biopsy provides an important information about the morphology and severity of the lesions, their classification, grades of activity and chronicity of the disease. With the appearance of any signs or symptoms of kidney disease such as hematuria, proteinuria, nephrotic syndrome or renal insufficiency the renal biopsy should be performed. Repeat kidney biopsies should also be done for clinical indications due to SLE flare, persistent proteinuria or declining renal function. The role of the renal biopsy in diagnosis, treatment, management, and follow-up of LN is critical, although to predict the outcome has been a matter of controversy [1, 7, 8]. Considering the importance of the biopsy making the treatment decision and determining the prognosis, it is essential to assess renal histopathology with high accuracy [9, 12, 13]. LN can affect all compartments of the kidney including glomeruli, tubules, interstitium and blood vessels. The analysis of the renal lesions is based on light microscopy (LM) associated with the immunofluorescence (IF) and electron microscopy (EM) findings [11].
