Purpose: Heart transplant candidates are evaluated for anti-HLA antibodies by Luminex single-antigen bead testing to avoid donors that may harbor antigens that these antibodies are against. To identify strongly-binding antibodies, the Luminex assay can be performed via a 1:8 dilution of the patient's serum. In addition, a C1q assay can be used to measure the ability of an antibody to bind complement and therefore have the potential to cause injury to a potential donor heart. It has been reported that the antibody binding strength described as mean fluorescent intensity (MFI) does not correlate to complement binding. However, 1:8 dilution may correlate to complement binding. We sought to assess whether there is a correlation between the Luminex 1:8 dilution assay and a positive C1q assay in patients awaiting heart transplant. This is important as many programs do not have the C1q assay available.

Methods: Between 2010 and 2016, we identified 42 patients with anti-HLA antibody on the Luminex 1:8 assay and divided them into groups of MFI > 2500, 5000 and 10000). We then evaluated these samples for complement fixation (C1q assay) on the same date of serum analysis.

Results: 32/51 patients (62.7%) with MFI >2500, 36/42 (85.7%) patients with MFI>5000, and 10/11 (90.9%) of patients with MFI>10000 on 1:8 dilution had positive C1q fixation. There was a significant difference between the three groups with respect to complement fixation (p=0.017).

Conclusion: The proportion of patients with positive complement fixation is significant for MFI >2500 which is the lowest MFI detected on our Luminex 1:8 dilution. Thus, it appears that detection of antibody with the Luminex 1:8 dilution is the poor man's C1q assay. The corresponding antigens for these anti-HLA antibodies should be avoided in a virtual crossmatch for these patients awaiting heart transplantation.

CITATION INFORMATION: Kittleson M., Patel J., Kransdorf E., Levine R., Dimbil S., Geft D., Chang D., Czer L., Kobashigawa J. What Threshold MFI is the Luminex 1:8 Dilution the Poor Man's C1q for Patients Awaiting Heart Transplant? Am J Transplant. 2017;17 (suppl 3).

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