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Abstract Number: 2798

Multi-Center Validation of Platelet Bound C4d, a Biomarker for Systemic Lupus Erythematosus

Richard Furie1, Anca D. Askanase2, Kenneth Kalunian3, Elena Massarotti4, Rosalind Ramsey-Goldman5, Daniel J Wallace6, Stuart L. Silverman7, Smitha Reddy8, Puja Chitkara9, Chaim Putterman10, Christopher Collins11, Jill P. Buyon12, Cristina Arriens13, Tyler O'Malley14, Roberta Alexander15, Derren Barken16, John Conklin17, Susan Manzi18, Joseph Ahearn19, Arthur Weinstein20 and Thierry Dervieux14, 1North Shore University Hospital, Great Neck, NY, 2Medicine, Rheumatology, Columbia University Medical Center, New York, NY, 3Center for Innovative Therapy, UCSD School of Medicine, La Jolla, CA, 4Rheumatology, Immunology, & Allergy, Harvard Medical School, Brigham & Women's Hosp, Boston, MA, 5FSM, Northwestern University, Chicago, IL, 6Division of Rheumatology, Cedars-Sinai Medical Center, Los Angeles, CA, 7Cedars, Beverly Hills, CA, 8Arthritis Care and Research Center, Inc., Poway, CA, 9Rheumatology, Center For Arthritis and Rheumatologic Excellence, Chula Vista, CA, 10Albert Einstein College of Medicine/Montefiore Medical Center, New York, NY, 11MedStar Washington Hospital Center, Washington, DC, 12Medicine, New York University School of Medicine, New York, NY, 13Arthritis & Clinical Immunology, Oklahoma Medical Research Foundation, Oklahoma City, OK, 14Research and Development, Exagen Diagnostics, Vista, CA, 15Research & Development, Exagen Diagnostics, Vista, CA, 16Exagen Diagnostics, Vista, CA, 171261 Liberty Way Suite C, Exagen Diagnostics, Vista, CA, 18Lupus Center of Excellence, West Penn Allegheny Health System, Pittsburgh, PA, 19Allegheny Singer Research Institute, Allegheny Health Network, Pittsburgh, PA, 20Rheumatology Section, Washington Hospital Center, Washington, DC

Meeting: 2016 ACR/ARHP Annual Meeting

Date of first publication: September 28, 2016

Keywords: Antiphospholipid antibodies, complement and systemic lupus erythematosus (SLE)

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Session Information

Date: Tuesday, November 15, 2016

Session Title: Systemic Lupus Erythematosus – Clinical Aspects and Treatment - Poster III: Biomarkers and Nephritis

Session Type: ACR Poster Session C

Session Time: 9:00AM-11:00AM

Background/Purpose:

Previous studies have established the value of measuring complement activation products (C4d) bound to platelets (PC4d) for the diagnosis and monitoring of Systemic Lupus Erythematosus (SLE). Separately, Antiphospholipid (APL) antibodies have been associated with complement activation and PC4d expression. In this study, we sought to validate the performance characteristics of PC4d, stratified by the presence or absence of APL antibodies.

Methods:

This multi-centered validation cross sectional study (16 sites in the US) enrolled 402 SLE subjects fulfilling the 1982 American College of Rheumatology Criteria revised in 1997 (mean age 41 years; 91% female), 411 subjects with rheumatic and autoimmune diseases other than SLE (mean age 55, 86% female consisting of 181 rheumatoid arthritis, 90 primary fibromyalgia, 92 other rheumatic diseases, and 48 autoimmune thyroiditis or hepatitis) and 198 healthy volunteers (mean age 41 years; 66% female). PC4d densities were determined using flow cytometry (expressed as mean fluorescence intensity [MFI]). Positive PC4d consisted of PC4d levels greater than 20 net MFI. Anti-cardiolipin IgG, anti-Beta-2-glycoprotein 1 IgG, or anti-Phosphatidylserine/Prothrombin (PSPT) complex IgG antibodies were determined using ELISA (INOVA diagnostics, San Diego, CA). Presence of APL antibodies consisted of any of these antibodies above manufacturer cutoff. SLE Disease activity was assessed using the non-serological SLE Disease Activity Index SELENA modification (ns-SELENA-SLEDAI, without the complement and anti-dsDNA). Performance characteristics were established using sensitivity, specificity, and ROC Curve Area Under the Curve (AUC). Statistical evaluation was by t-test (for disease activity), by chi-squared test for equality of proportions (for sensitivities and specificities) and by the method of DeLong (for ROC Curve AUC).

Results:

PC4d was highly specific in distinguishing SLE from other rheumatic diseases (Table) and normals. Among SLE subjects, 47% (n=187) presented with at least one APL antibody as compared to 21% (n=86) of subjects with other diseases and 15% of normals. PC4d sensitivity for SLE was higher among APL positive subjects by comparison to APL negative subjects (p=0.003). Specificity was not significantly different between APL positive and negative subjects (p>0.372). ROC AUC was significantly higher among the APL positive compared to negative subjects (p=0.002). The incidence of APL antibodies among all PC4d positive subjects was 60% compared to 27% among PC4d negative subjects (p<0.001). SLE subjects presenting with positive PC4d had higher disease activity (4.1±0.5) than those presenting with negative PC4d (3.0±0.2) (p=0.03).

Conclusion:

We confirm that PC4d is highly specific for SLE, and is associated with disease activity.


Disclosure: R. Furie, exagen, 2; A. D. Askanase, anca askanase, 2; K. Kalunian, Exagen, 2; E. Massarotti, Exagen, 2; R. Ramsey-Goldman, exagen, 2; D. J. Wallace, Exagen, 2; S. L. Silverman, Exagen, 2; S. Reddy, Exagen, 2; P. Chitkara, exagen, 2; C. Putterman, exagen, 2; C. Collins, Exagen, 2; J. P. Buyon, exagen, 2; C. Arriens, Exagen, 2; T. O'Malley, exagen, 3; R. Alexander, exagen, 3; D. Barken, Exagen, 3; J. Conklin, Exagen, 3; S. Manzi, exagen, 2; J. Ahearn, exagen, 2; A. Weinstein, exagen, 6; T. Dervieux, Exagen, 3.

To cite this abstract in AMA style:

Furie R, Askanase AD, Kalunian K, Massarotti E, Ramsey-Goldman R, Wallace DJ, Silverman SL, Reddy S, Chitkara P, Putterman C, Collins C, Buyon JP, Arriens C, O'Malley T, Alexander R, Barken D, Conklin J, Manzi S, Ahearn J, Weinstein A, Dervieux T. Multi-Center Validation of Platelet Bound C4d, a Biomarker for Systemic Lupus Erythematosus [abstract]. Arthritis Rheumatol. 2016; 68 (suppl 10). https://acrabstracts.org/abstract/multi-center-validation-of-platelet-bound-c4d-a-biomarker-for-systemic-lupus-erythematosus/. Accessed January 27, 2021.
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