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Lupus nephritis (LN) is a severe manifestation of systemic lupus erythematosus (SLE), characterized by chronic and progressive inflammation of the kidneys. As with many other autoimmune diseases, LN is a multifactorial disease caused by genetic and environmental factors. Globally, LN can affect around 60% of SLE patients, and it was observed to be less frequent and severe in Caucasian patients compared to other ethnic groups, including Arabs. Data on LN in the United Arab Emirates (UAE) are scattered and scarce in literature. Nevertheless, LN is common, occurring in around 43%-55% of SLE patients in the UAE. Anecdotally, the demographics and clinical features of SLE in the UAE have been distinct. However, the paucity of supporting literature makes it difficult to draw meaningful conclusions. Over the past two decades, there have been improvements in understanding the pathogenesis of LN; however, many cellular and molecular mechanisms which are implicated in the disease development and progression remain ambiguous. Investigating the clinical, pathological, and genetic characteristics of LN in different cohorts of patients is of importance for a better understanding of its pathogenesis, and thus improving its outcome. As a result, we acknowledge the need for large-scale epidemiological, clinical, and genetic investigation of LN cohorts in the UAE and surrounding regions.

Objectives: The renal activity index for lupus (RAIL) measures lupus nephritis (LN) activity considering urine levels of 6 biomarkers (neutrophil gelatinase-associated lipocalin, monocyte chemoattractant protein-1, kidney injury molecule-1, adiponectin, haemopexin, ceruloplasmin). We aimed to compare the accuracy of the RAIL and the renal domain-score of the SLE disease activity index (rSLEDAI) in detecting LN activity., Methods: Random urine samples of patients with childhood-onset SLE with and without LN were assayed and scores of the RAIL, and RAIL standardised for urine creatinine (RAIL-Cr) were calculated. Clinical LN activity was measured by the rSLEDAI, and histological activity of LN was categorised as inactive/low-moderate/high for National Institute of Health-activity index scores of <2/2-10/>10, respectively., Results: 115 patients were included in the analysis (47 patients without and 68 with LN). RAIL, RAIL-Cr and rSLEDAI scores at the time (±3 months) of kidney biopsy were available for 32 patients. Median rSLEDAI, RAIL and RAIL-Cr values were 4, -0.04, 0.02 for inactive LN, 12, 0.7 and 0.9 for low-moderate LN activity and 12, 2 and 1.8 for high LN activity, respectively. The area under the receiver operating characteristic curve (AUC) to capture high LN activity was the lowest for the rSLEDAI (AUC=0.62), followed by the RAIL-Cr (AUC=0.73) and RAIL (AUC=0.79). Notably, when testing urine samples collected during routine clinic visits remote (>3 months) from a kidney biopsy, 50% patients with rSLEDAI scores of 0 had RAIL scores reflecting low-moderate LN activity., Conclusion: Monitoring of renal inflammation in children and adolescents with SLE can be improved by the measurement of urine biomarkers. The RAIL may constitute important auxiliary tool for the surveillance of LN in a clinical setting and assist with the decision to obtain a kidney biopsy., Competing Interests: Competing interests: SEW has a consultation agreement with Bristol-Myers Squibb in 2020 for an unrelated project on paediatric lupus nephritis., (© Author(s) (or their employer(s)) 2022. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Objective: To compare the diagnostic usefulness of the 2019 European League Against Rheumatism (EULAR)/American College of Rheumatology (ACR) classification criteria for systemic lupus erythematosus (SLE) to that of the 1997 ACR classification criteria for SLE when applied to youths (age ≤21 years) with SLE., Methods: Data were extracted from electronic health records of patients followed at a large academic pediatric hospital. The treating rheumatologist's diagnosis of SLE served as the standard criterion for identifying SLE patients (cases). Controls were patients with juvenile dermatomyositis (DM), juvenile scleroderma, or juvenile systemic sclerosis (SSc). The 2019 EULAR/ACR criteria and the 1997 ACR criteria were tested against the standard criterion., Results: A total of 112 SLE patients ages 2-21 years and 105 controls ages 1-19 years (66% juvenile DM, 34% juvenile scleroderma or juvenile SSc) were available for analysis. The 2019 EULAR/ACR criteria had significantly higher sensitivity (85% versus 72%; P = 0.023) and similar specificity (83% versus 87%; P = 0.456) than the 1997 ACR criteria. The mean ± SD 2019 EULAR/ACR classification summary scores were significantly higher among non-White than White patients (22.41 ± 10.04 versus 17.59 ± 9.19; P < 0.01). The sensitivity of the 2019 EULAR/ACR criteria in non-White/White patients was 92%/80% (P = 0.08) versus 83%/64% (P < 0.02) for the 1997 ACR criteria. The sensitivity of the 2019 EULAR/ACR criteria was not affected by age or sex., Conclusion: The 2019 EULAR/ACR criteria efficiently classify youths with SLE, irrespective of age, sex, and race. Compared to the 1997 ACR criteria, the new criteria are significantly more sensitive and similarly specific in youths with SLE., (© 2020, American College of Rheumatology.)