Analysis of Erythrocyte C4d to Complement Receptor 1 Ratio: Use in Distinguishing between Infection and Flare-Up in Febrile Patients with Systemic Lupus Erythematosus.
OBJECTIVE
Fever in systemic lupus erythematosus (SLE) can be caused by infection or flare-up of the disease. This study aimed to determine whether the ratio of the level of erythrocyte-bound C4d to that of complement receptor 1 (C4d/CR1) can serve as a useful biomarker in the differentiation between infection and flare-up in febrile SLE patients.


METHODS
We enrolled febrile SLE patients and determined the ratio on the day of admission. The patients were divided into 2 groups according to the subsequent clinical course.


RESULTS
Among the febrile SLE patients, those with flare-up had higher ratios and lower C-reactive protein (CRP) levels than those with infection. Cut-off values of <1.2447 and >4.67 for C4d/CR1 ratio and CRP, respectively, were 40.91% sensitive and 100.0% specific for the presence of infection in febrile SLE patients; similarly, cut-off values of >1.2447 and <2.2, respectively, were 80% sensitive and 100% specific for the absence of infection in febrile SLE patients.


CONCLUSIONS
The C4d/CR1 ratio is a simple and quickly determinable biomarker that enables the differentiation between infection and flare-up in febrile SLE patients at initial evaluation. Further, when combined with the CRP level, it is useful to evaluate disease activity in SLE patients with infection.
Graduate Institute of Clinical Medicine, Taipei Medical University, Taipei 11031, Taiwan ; Division of Rheumatology, Immunology and Allergy, Department of Internal Medicine, Taipei Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation, School of Medicine, Tzu Chi University, Hualien 970, Taiwan ; Division of Rheumatology, Immunology and Allergy, Department of Internal Medicine, Tri-Service General Hospital, National Defense Medical Center, Taipei 11490, Taiwan.
Chen-Hung
CH
Chen
Division of Rheumatology, Immunology and Allergy, Department of Internal Medicine, Armed-Forces Zuoying General Hospital, Kaohsiung 81342, Taiwan.
Shun-Ban
SB
Tai
Division of Rheumatology, Immunology and Allergy, Department of Internal Medicine, Tri-Service General Hospital, National Defense Medical Center, Taipei 11490, Taiwan.
Hsiang-Cheng
HC
Chen
Division of Rheumatology, Immunology and Allergy, Department of Internal Medicine, Armed-Forces Taichung General Hospital, Taichung 41168, Taiwan.
Deng-Ho
DH
Yang
Division of Infection, Department of Internal Medicine, Taipei Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation, School of Medicine, Tzu Chi University, Hualien 970, Taiwan.
Ming-Yieh
MY
Peng
Graduate Institute of Clinical Medicine, Taipei Medical University, Taipei 11031, Taiwan ; Division of Nephrology, Department of Medicine, Shuang Ho Hospital, Taipei Medical University, New Taipei 23561, Taiwan.
Yuh-Feng
YF
Lin
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers; D015935:Complement C4b; D003937:Diagnosis, Differential; D004912:Erythrocytes / Q000378:metabolism*; D005260:Female; D005334:Fever / Q000097:blood / Q000175:diagnosis*; D006801:Humans; D007239:Infections / Q000097:blood / Q000175:diagnosis*; D008180:Lupus Erythematosus, Systemic / Q000097:blood / Q000175:diagnosis*; D008297:Male; D008875:Middle Aged; D010446:Peptide Fragments / Q000097:blood*; D011951:Receptors, Complement / Q000097:blood*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D055815:Young Adult
D015415:Biomarkers; D010446:Peptide Fragments; D011951:Receptors, Complement; D015935:Complement C4b; C032261:complement C4d