Lupus nephritis is an early manifestation in the development of systemic lupus erythematosus that worsens the morbidity and mortality of these patients. Objective: To study the form of presentation in patients with lupus nephritis, the clinical and immunological characteristics, and their relationship with renal histology. Patients and Method: Retrospective study in children under 18 years of age, with lupus nephritis, in follow-up in a third level children's hospital in Madrid, between January 2012 and May 2020. We recorded demographic, clinical, and laboratory data (blood count, renal function, liver function, protein, ionogram, blood glucose, uric acid, lactate dehydrogenase, coagulation, and urine analysis), as well as immunological data (immunoglobulins, antinuclear antibodies, complement, and lupus anticoagulant), and histological classification data. Descriptive analysis and analysis of associations between variables was performed, with a significant p < 0.05. Results: 16 patients (11 women) were included, the median age at presentation was 10.6 +/- 2.3 years (5.7-15.3). The median time between symptoms onset and renal involvement was 6.3 months +/- 10.5 (range 0 - 33.6). Renal involvement was the initial manifestation in 37.5% of patients. 50% had arthralgias or arthritis prior to diagnosis, and 25% had fever and constitutional symptoms (asthenia, anorexia, and/or weight loss). The most frequent form of renal involvement was microhematuria associated with proteinuria in non-nephrotic range. In the renal anatomo-pathological study, according to the ISN/RPS 2003 classification, grades III (46.6%) and IV (33.3%) predominated. Conclusions: Six patients presented renal involvement at baseline with musculoskeletal involvement being more frequent. Most patients (86.6%) presented advanced lupus nephritis in the histological study at diagnosis. Immunologic involvement was the only marker that correlated with systemic involvement.
