Clin Rheumatol DOI 10.1007/s10067-014-2843-4
ORIGINAL ARTICLE
Diagnostic value of serum complement C3 and C4 levels in Chinese patients with systemic lupus erythematosus Hejun Li & Shunping Lin & Shangchih Yang & Ling Chen & Xiangxiong Zheng
Received: 27 June 2014 / Revised: 20 November 2014 / Accepted: 4 December 2014 # International League of Associations for Rheumatology (ILAR) 2015
Abstract In 2009, hypocomplementemia involving C3, C4, and total hemolytic complement (CH50) was proposed as an immunologic criterion to enhance the sensitivity of systemic lupus erythematosus (SLE) classification criteria. This study evaluated the diagnostic value of low serum complement C3 and C4 levels in Chinese patients with SLE. In total, 2452 patients were enrolled in this study (158 with SLE and 2294 with other diseases). Receiver operating characteristic analysis showed that the optimal C3 and C4 cut-off levels for a diagnosis of SLE were 0.785 g/L (sensitivity, 77.9 %; specificity, 81.5 %) and 0.145 g/L (sensitivity, 80.1 %; specificity, 83.2 %), respectively. The prevalence of a low C3 or C4 level alone was similar between patients with SLE and those with other diseases, while the prevalence of simultaneously low C3 and C4 levels was higher in patients with SLE (73.42 %). Antinuclear antibody had a high sensitivity (96.64 %) and low negative likelihood ratio (0.04). Hypocomplementemia with positive antinuclear antibody had a high positive likelihood ratio. Inclusion of hypocomplementemia as a classification criterion for SLE resulted in a 16.18 % increase in the number of patients assigned to the SLE group (from 136 to 158 patients). Hypocomplementemia was highly prevalent in patients with hematological disease (41.94 %). These results suggest that hypocomplementemia has important diagnostic value for SLE by improving the sensitivity of the diagnosis of SLE. C3 and C4 should be tested simultaneously because a Hejun Li and Shunping Lin are contributed equally to this work. H. Li (*) : S. Lin : L. Chen : X. Zheng (*) Department of Rheumatology, Union Hospital, Fujian Medical University, 29 Xinquan Road, Fuzhou 350001, China e-mail: [email protected] e-mail: [email protected] S. Yang Department of Internal Medicine, Chang Gung Memorial Hospital, Xiamen, China
low C3 or C4 level alone is not a suitable immunological criterion. Keywords Antinuclear antibody . Complement . Diagnostic value . Systemic lupus erythematosus
Introduction Systemic lupus erythematosus (SLE) is a diffuse immunemediated, chronic inflammatory disease of the connective tissue. Various antinuclear antibodies (ANAs) that affect multiple organ systems are produced in patients with SLE. Women of childbearing age are commonly affected. In China, SLE occurs at an incidence of approximately 70 per 100,000 individuals and 113 per 100,000 women [1]. SLE has high heterogeneity, a complex pathophysiology and various clinical manifestations. Patients can exhibit different clinical manifestations and autoantibodies, and no single test is sensitive or specific enough for a diagnosis [2]. The clinical diagnosis of SLE is currently based on the American College of Rheumatology SLE classification criteria. However, this classification system has limitations in clinical practice; therefore, more sensitive and specific biomarkers are needed to improve the effectiveness and diagnostic accuracy. The Systemic Lupus International Collaborating Clinics (SLICC) group proposed hypocomplementemia involving C3, C4, and total hemolytic complement (CH50) as an immunologic criterion in 2009 to enhance the sensitivity of the SLE classification criteria [3]. Compared with other new biomarkers such as complement activation fragments C3a, C5a, C3d, and C4d [4] (indicators that are relatively expensive, unnecessary for clinical diagnosis in many cases, and not routinely assayed), complement C3 and C4 are more stable and easier to detect routinely in most hospitals.
Clin Rheumatol
Because SLE has variable clinical manifestations, all biomarkers, including hypocomplementemia, in patients with SLE may only represent one aspect of the disease, not the whole spectrum. There is still some uncertainty about the use of the SLE classification criteria in clinical practice. These criteria must be properly assessed and applied to improve diagnostic sensitivity and reduce misdiagnosis. In this study, we systematically evaluated the diagnostic value of C3 and C4 levels in a large cohort of Chinese patients with SLE as the first study of its kind.
Nephropathy included proteinuria, hematuria, and renal insufficiency. Of all patients with these diseases, 40 only underwent C3 measurement, 218 underwent both C3 and C4 measurement, and 42 did not undergo ANA measurement. Other diseases included oncological, infectious, nervous, and cardiovascular diseases. Of all patients with these diseases, 79 only underwent C3 measurement, 969 underwent both C3 and C4 measurement, and 331 did not undergo ANA measurement.
Patients and methods
Methods
Patients
Complement detection was performed by immunization rate scattering turbidimetry (Beckman Coulter, Inc., Brea, CA, USA). The reference level of C3 was 0.79 to 1.52 g/L, and that for C4 was 0.16 to 0.38 g/L. ANA was detected by indirect immunofluorescence using a Euroimmun kit (Euroimmun Medizinische Labordiagnostika AG, Beijing, China) with HEp-2 as the substrate. The results are presented as negative, weakly positive, or positive (+, ++, or +++, respectively).
This was a retrospective case-control study on the Chinese Han population. The complement levels in 3922 blood samples were measured at Fujian Medical University Union Hospital from August 2012 to August 2013. After reexamination of 1451 cases, 18 cases of incomplete data and 1 case of druginduced lupoid syndrome were excluded. The remaining blood samples collected from 2452 newly diagnosed patients were analyzed: 158 patients with first-onset SLE, 622 with non-SLE rheumatic disease, 366 with hematological disease, 258 with nephropathy, and 1048 with other diseases. All clinical data were collected through outpatient and admission numbers. Patients with SLE were divided into two groups: SLE-1 (n=136; 1 patient also had primary biliary cirrhosis and 1 also had rheumatoid arthritis) and SLE-2 (n=22; 1 patient also had systemic sclerosis). The including criteria for the SLE-1 group were first-onset patients who had biopsyproven lupus nephritis with ANA or anti-dsDNA OR satisfied at least 4 of the 16 SLICC SLE classification criteria (excluding low complement, i.e., only the other 5 immunologic criteria plus all 11 clinical criteria were used for diagnosis). The including criteria for the SLE-2 group were first-onset patients who had low complement plus three of the other classification criteria. The excluding criteria for both SLE groups was relapsed SLE. Patients with SLE with concurrent infection were also included in the study. All patients with SLE were tested for C3, C4, and ANA levels. Non-SLE rheumatic diseases included non-SLE diffuse connective tissue disease, primary vasculitis, spondyloarthritis, and metabolic joint disease. Of all patients with these diseases, 31 only underwent C3 measurement, 591 underwent both C3 and C4 measurement, and 104 did not undergo ANA measurement. Hematological diseases included leukemia, myelodysplastic syndromes, lymphoma, chronic myeloproliferative disorders, and non-autoimmune-induced anemia, thrombocytopenia, or leukopenia. Of all patients with these diseases, 25 only underwent C3 measurement, 341 underwent both C3 and C4 measurement, and 67 did not undergo ANA measurement.
Statistical analyses A receiver operating characteristics (ROC) curve was formulated by SPSS 12.0 statistical software. The SLE-1 group was defined as the lupus group, and patients with non-SLE rheumatic disease, hematological disease, nephropathy, and other diseases were defined as the control group. Chi-squared statistical analysis was used to compare the differences in the low complement levels and ANA positive rates between the groups. Sensitivity, specificity, accuracy, positive and negative predictive values, and positive and negative likelihood ratios were calculated to analyze the diagnostic value of low complement and ANA positivity for SLE.
Results The SLE-1 group comprised 24 men and 112 women with a mean age of 35.12±14.36 years (range, 7–67 years). The median number of accumulated SLICC criteria was 5 (range 4–8). The median duration from clinical onset to disease diagnosis was 3.35 months (interquartile range 23.00). The median Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) score was 9 (range 3–22). The SLE-2 group comprised 3 men and 19 women with a mean age of 36.82± 15.92 years (range 10–63 years). The number of accumulated SLICC criteria was 4. The median duration from clinical onset
Clin Rheumatol
to diagnosis was 9.50 months (interquartile range 21.75). The median SLEDAI score was seven (range 3–14). The ROC analysis curve showed that the optimal clinical cut-off level of C3 was 0.785 g/L, which had 77.9 % sensitivity and 81.5 % specificity. The optimal cut-off level of C4 was 0.145 g/L, which had 80.1 % sensitivity and 83.2 % specificity. There was no statistically significant difference in the area under the ROC curve between C3 and C4 (p>0.05) (Fig. 1 and Table 1). The prevalence of a low C3 or C4 level alone (6.33 and 10.76 %, respectively) in patients with SLE was not higher than that in patients without SLE (p>0.05). The prevalence of a low C3 level alone in patients with SLE was lower than that in patients with hematological disease (14.37 %) and nephropathy (15.60 %) (p
ORIGINAL ARTICLE
Diagnostic value of serum complement C3 and C4 levels in Chinese patients with systemic lupus erythematosus Hejun Li & Shunping Lin & Shangchih Yang & Ling Chen & Xiangxiong Zheng
Received: 27 June 2014 / Revised: 20 November 2014 / Accepted: 4 December 2014 # International League of Associations for Rheumatology (ILAR) 2015
Abstract In 2009, hypocomplementemia involving C3, C4, and total hemolytic complement (CH50) was proposed as an immunologic criterion to enhance the sensitivity of systemic lupus erythematosus (SLE) classification criteria. This study evaluated the diagnostic value of low serum complement C3 and C4 levels in Chinese patients with SLE. In total, 2452 patients were enrolled in this study (158 with SLE and 2294 with other diseases). Receiver operating characteristic analysis showed that the optimal C3 and C4 cut-off levels for a diagnosis of SLE were 0.785 g/L (sensitivity, 77.9 %; specificity, 81.5 %) and 0.145 g/L (sensitivity, 80.1 %; specificity, 83.2 %), respectively. The prevalence of a low C3 or C4 level alone was similar between patients with SLE and those with other diseases, while the prevalence of simultaneously low C3 and C4 levels was higher in patients with SLE (73.42 %). Antinuclear antibody had a high sensitivity (96.64 %) and low negative likelihood ratio (0.04). Hypocomplementemia with positive antinuclear antibody had a high positive likelihood ratio. Inclusion of hypocomplementemia as a classification criterion for SLE resulted in a 16.18 % increase in the number of patients assigned to the SLE group (from 136 to 158 patients). Hypocomplementemia was highly prevalent in patients with hematological disease (41.94 %). These results suggest that hypocomplementemia has important diagnostic value for SLE by improving the sensitivity of the diagnosis of SLE. C3 and C4 should be tested simultaneously because a Hejun Li and Shunping Lin are contributed equally to this work. H. Li (*) : S. Lin : L. Chen : X. Zheng (*) Department of Rheumatology, Union Hospital, Fujian Medical University, 29 Xinquan Road, Fuzhou 350001, China e-mail: [email protected] e-mail: [email protected] S. Yang Department of Internal Medicine, Chang Gung Memorial Hospital, Xiamen, China
low C3 or C4 level alone is not a suitable immunological criterion. Keywords Antinuclear antibody . Complement . Diagnostic value . Systemic lupus erythematosus
Introduction Systemic lupus erythematosus (SLE) is a diffuse immunemediated, chronic inflammatory disease of the connective tissue. Various antinuclear antibodies (ANAs) that affect multiple organ systems are produced in patients with SLE. Women of childbearing age are commonly affected. In China, SLE occurs at an incidence of approximately 70 per 100,000 individuals and 113 per 100,000 women [1]. SLE has high heterogeneity, a complex pathophysiology and various clinical manifestations. Patients can exhibit different clinical manifestations and autoantibodies, and no single test is sensitive or specific enough for a diagnosis [2]. The clinical diagnosis of SLE is currently based on the American College of Rheumatology SLE classification criteria. However, this classification system has limitations in clinical practice; therefore, more sensitive and specific biomarkers are needed to improve the effectiveness and diagnostic accuracy. The Systemic Lupus International Collaborating Clinics (SLICC) group proposed hypocomplementemia involving C3, C4, and total hemolytic complement (CH50) as an immunologic criterion in 2009 to enhance the sensitivity of the SLE classification criteria [3]. Compared with other new biomarkers such as complement activation fragments C3a, C5a, C3d, and C4d [4] (indicators that are relatively expensive, unnecessary for clinical diagnosis in many cases, and not routinely assayed), complement C3 and C4 are more stable and easier to detect routinely in most hospitals.
Clin Rheumatol
Because SLE has variable clinical manifestations, all biomarkers, including hypocomplementemia, in patients with SLE may only represent one aspect of the disease, not the whole spectrum. There is still some uncertainty about the use of the SLE classification criteria in clinical practice. These criteria must be properly assessed and applied to improve diagnostic sensitivity and reduce misdiagnosis. In this study, we systematically evaluated the diagnostic value of C3 and C4 levels in a large cohort of Chinese patients with SLE as the first study of its kind.
Nephropathy included proteinuria, hematuria, and renal insufficiency. Of all patients with these diseases, 40 only underwent C3 measurement, 218 underwent both C3 and C4 measurement, and 42 did not undergo ANA measurement. Other diseases included oncological, infectious, nervous, and cardiovascular diseases. Of all patients with these diseases, 79 only underwent C3 measurement, 969 underwent both C3 and C4 measurement, and 331 did not undergo ANA measurement.
Patients and methods
Methods
Patients
Complement detection was performed by immunization rate scattering turbidimetry (Beckman Coulter, Inc., Brea, CA, USA). The reference level of C3 was 0.79 to 1.52 g/L, and that for C4 was 0.16 to 0.38 g/L. ANA was detected by indirect immunofluorescence using a Euroimmun kit (Euroimmun Medizinische Labordiagnostika AG, Beijing, China) with HEp-2 as the substrate. The results are presented as negative, weakly positive, or positive (+, ++, or +++, respectively).
This was a retrospective case-control study on the Chinese Han population. The complement levels in 3922 blood samples were measured at Fujian Medical University Union Hospital from August 2012 to August 2013. After reexamination of 1451 cases, 18 cases of incomplete data and 1 case of druginduced lupoid syndrome were excluded. The remaining blood samples collected from 2452 newly diagnosed patients were analyzed: 158 patients with first-onset SLE, 622 with non-SLE rheumatic disease, 366 with hematological disease, 258 with nephropathy, and 1048 with other diseases. All clinical data were collected through outpatient and admission numbers. Patients with SLE were divided into two groups: SLE-1 (n=136; 1 patient also had primary biliary cirrhosis and 1 also had rheumatoid arthritis) and SLE-2 (n=22; 1 patient also had systemic sclerosis). The including criteria for the SLE-1 group were first-onset patients who had biopsyproven lupus nephritis with ANA or anti-dsDNA OR satisfied at least 4 of the 16 SLICC SLE classification criteria (excluding low complement, i.e., only the other 5 immunologic criteria plus all 11 clinical criteria were used for diagnosis). The including criteria for the SLE-2 group were first-onset patients who had low complement plus three of the other classification criteria. The excluding criteria for both SLE groups was relapsed SLE. Patients with SLE with concurrent infection were also included in the study. All patients with SLE were tested for C3, C4, and ANA levels. Non-SLE rheumatic diseases included non-SLE diffuse connective tissue disease, primary vasculitis, spondyloarthritis, and metabolic joint disease. Of all patients with these diseases, 31 only underwent C3 measurement, 591 underwent both C3 and C4 measurement, and 104 did not undergo ANA measurement. Hematological diseases included leukemia, myelodysplastic syndromes, lymphoma, chronic myeloproliferative disorders, and non-autoimmune-induced anemia, thrombocytopenia, or leukopenia. Of all patients with these diseases, 25 only underwent C3 measurement, 341 underwent both C3 and C4 measurement, and 67 did not undergo ANA measurement.
Statistical analyses A receiver operating characteristics (ROC) curve was formulated by SPSS 12.0 statistical software. The SLE-1 group was defined as the lupus group, and patients with non-SLE rheumatic disease, hematological disease, nephropathy, and other diseases were defined as the control group. Chi-squared statistical analysis was used to compare the differences in the low complement levels and ANA positive rates between the groups. Sensitivity, specificity, accuracy, positive and negative predictive values, and positive and negative likelihood ratios were calculated to analyze the diagnostic value of low complement and ANA positivity for SLE.
Results The SLE-1 group comprised 24 men and 112 women with a mean age of 35.12±14.36 years (range, 7–67 years). The median number of accumulated SLICC criteria was 5 (range 4–8). The median duration from clinical onset to disease diagnosis was 3.35 months (interquartile range 23.00). The median Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) score was 9 (range 3–22). The SLE-2 group comprised 3 men and 19 women with a mean age of 36.82± 15.92 years (range 10–63 years). The number of accumulated SLICC criteria was 4. The median duration from clinical onset
Clin Rheumatol
to diagnosis was 9.50 months (interquartile range 21.75). The median SLEDAI score was seven (range 3–14). The ROC analysis curve showed that the optimal clinical cut-off level of C3 was 0.785 g/L, which had 77.9 % sensitivity and 81.5 % specificity. The optimal cut-off level of C4 was 0.145 g/L, which had 80.1 % sensitivity and 83.2 % specificity. There was no statistically significant difference in the area under the ROC curve between C3 and C4 (p>0.05) (Fig. 1 and Table 1). The prevalence of a low C3 or C4 level alone (6.33 and 10.76 %, respectively) in patients with SLE was not higher than that in patients without SLE (p>0.05). The prevalence of a low C3 level alone in patients with SLE was lower than that in patients with hematological disease (14.37 %) and nephropathy (15.60 %) (p
