correspondence n engl j med 370;1 nejm.org january 2, 2014 83 As Macchia and colleagues highlight, our data show that the change in 6-minute walk distance was not associated with long-term outcomes in pulmonary arterial hypertension. The observed reduction in morbidity was driven by a decrease in the rate of worsening of pulmonary arterial hypertension, which was defined in great detail and required three criteria, not only a decrease in the 6-minute walk distance. Our study was approved by health authorities and ethics com- mittees. Background therapy for pulmonary ar- terial hypertension, when available, was allowed, and we closely monitored patients for the need for additional treatment. In some countries, because of the limited availability of approved targeted therapies, a patient’s participation in a clinical trial may provide the only access to potential treatment for pulmonary arterial hypertension. Tomás Pulido, M.D. Ignacio Chávez National Heart Institute Mexico City, Mexico Lewis J. Rubin, M.D. University of California, San Diego La Jolla, CA Gérald Simonneau, M.D. Université Paris-Sud Le Kremlin-Bicêtre, France Since publication of their article, the authors report no fur- ther potential conflict of interest. 1. Graf C, Battisti WP, Bridges D, et al. Research methods and reporting: good publication practice for communicating com- pany sponsored medical research: the GPP2 guidelines. BMJ 2009;339:b4330. 2. AMWA position statement on the contribution of medical writers to scientific publications. Rockville, MD: American Medical Writers Association (http://www.amwa.org). 3. Jacobs A, Wager E. European Medical Writers Association (EMWA) guidelines on the role of medical writers in developing peer-reviewed publications. Curr Med Res Opin 2005;21:317-22. 4. Norris R, Bowman A, Fagan JM, et al. International Society for Medical Publication Professionals (ISMPP) position state- ment: the role of the professional medical writer. Curr Med Res Opin 2007;23:1837-40. DOI: 10.1056/NEJMc1313112 Complement-Binding Anti-HLA Antibodies and Kidney Transplantation To the Editor: Loupy et al. (Sept. 26 issue) 1 present data showing that the C1q-binding assay is more sensitive than the standard complement- dependent microlymphocytotoxicity (CDL) assay for assessing the risk of graft loss. In their retro- spective analysis of 1016 patients who had a neg- ative CDL assay before transplantation, antibody- mediated rejection developed in 7.4% during the first year. The authors predict that antibody-me- diated rejection would have occurred in 3.7% of patients (a 50% reduction) if the C1q-binding as- say had been used. However, most laboratories use a more sen- sitive flow cytometric crossmatching (FCXM), 2 not CDL alone. We have data from 11 patients who had low levels of donor-specific anti-HLA antibodies (mean fluorescence intensity [MFI], <3500 arbitrary fluorescence units) on the single- antigen Luminex bead assay, negative FCXM, and negative C1q-binding assay (<100 MFI units) Table 1. Levels of Donor-Specific Anti-HLA Antibodies in Four Patients with Antibody-Mediated Rejection after Kidney Transplantation.* Patient Number Before Transplantation After Transplantation Luminex Assay C1q Assay Luminex Assay C1q Assay 1 B72 (MFI, 1632); CW2 (MFI, 4758) B72 (MFI, 0); CW2 (MFI, 0) B72 (MFI, 3123); CW2 (MFI, 8214) B72 (MFI, 21,609); CW2 (MFI, 10,096) 2 B8 (MFI, 350); A23 (MFI, 1237) B8 (MFI, 100); A23 (MFI, 0) B8 (MFI, 4115); A23 (MFI, 1166) B8 (MFI, 1839); A23 (MFI, 157) 3 B49 (MFI, 0); DQ2 (MFI, 275) B49 (MFI, 16); DQ2 (MFI, 0) B49 (MFI, 8888); DQ2 (MFI, 1094) B49 (MFI, 1609); DQ2 (MFI, 638) 4 B37 (MFI, 871); B51 (MFI, 473) B37 (MFI, 0); B51 (MFI, 24) B37 (MFI, 2669); B51 (MFI, 618) B37 (MFI, 1115); B51 (MFI, 386) * The mean fluorescence intensity (MFI) was measured in arbitrary fluorescence units. The New England Journal of Medicine ownloaded from nejm.org at CHARITE CAMPUS CHARITE MITTE MEDIZINISCHE BIBLIO on February 14, 2014. For personal use only. No other uses without permission Copyright © 2014 Massachusetts Medical Society. All rights reserved.