The clinical characteristics of low C4 alone in patients with systemic lupus erythematosus
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LETTERS OF BIOMEDICAL AND CLINICAL RESEARCH
The clinical characteristics of low C4 alone in patients with systemic lupus erythematosus Weiji Xie 1 & Zeen Xiao 1 & Jing Xu 1 & Guitian Hong 1 & Xiaochang Xu 2 & Yimin Zhang 2 & Xialan Zhang 3 Received: 2 May 2020 / Revised: 10 August 2020 / Accepted: 24 August 2020 # International League of Associations for Rheumatology (ILAR) 2020
Introduction Systemic lupus erythematosus (SLE) is a complex autoimmune disease, and one of the pathogenic mechanisms of SLE is the formation of an immune complex that then activates the complement system, resulting in complement consumption. Therefore, hypocomplementemia often occurs in patients with SLE. In clinical practice, patients with hypocomplementemia may exhibit low levels of C3 or C4 alone, and the pathogenic mechanism and clinical characteristics of these patients may differ from those of patients that show low levels of both C3 and C4. A study in Japan found a lower prevalence of arthritis, serositis, and nephritis in patients with low C3 levels alone [1]. Although SLE with low levels of C4 alone is common in clinical practice [2, 3], the potential features of SLE patients with low C4 levels alone remain unclear. In this study, we explored the clinical characteristics of SLE patients with low C4 alone.
Materials and methods The included patients were treated at The Second Affiliated Hospital of Shantou University Medical College and The Sixth Affiliated Hospital of Sun Yat-sen University from January 2016 to December 2018. Eligible patients needed to fulfill the 1997 criteria for the classification of SLE [4]. The
inclusion criteria were as follows: (1) a low level of C4 and (2) an age from 10 to 80 years. The exclusion criteria were as follows: (1) malignancy, pregnancy, hepatopathy, and infection; (2) rheumatoid arthritis, scleroderma, polymyositis, and Sjogren’s syndrome; and (3) treatment with dialysis. All procedures involving human participants were performed in accordance with the ethical standards of the appropriate institutional and/or national research committee and the 1964 Declaration of Helsinki and its later amendments or comparable ethical standards. Informed consent was obtained from all individual participants included in the study. S e r u m C 3 a n d C 4 l e v e l s w er e d e t er m i n e d b y immunonephelometry (Beckman AU5811 biochemical analyzer, Beckman Coulter, Inc., USA). The laboratory reference range for C3 was 0.79–1.52 g/L, while that for C4 was 0.20– 0.40 g/L. Based on the reference ranges, the patients were then divided into the low-C4 group (patients with low levels of C4 but normal levels of C3) or both-low group (patients with low levels of both C3 and C4). The full inclusion and exclusion criteria and grouping protocols are detailed in Fig. 1. The clinical manifestations examined were skin abnormalities; arthritis; and renal, neurologic, and hematologic manifestations according to the 1997 criteria for the classification of SLE [4], and only manifestations that occurred within 1 week pri
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