We identified 15 sensitized pediatric and adult heart recipients with a calculated panel reactive antibody >50 % . Sera were tested by conventional SAB antibody testing using undiluted or 1:16 diluted sera and were compared to C1q results. Pre- and post-transplant DSA by both methods were correlated with XM and early AMR.
In 9 samples, individual Class I antibodies measured by SAB testing in undiluted sera correlated poorly with C1q reactivity (R2 = 0.07). In contrast, using sera diluted 1:16, conventional SAB results correlated better with C1q testing ( R2 = 0.73). Receiver operator characteristic curve analysis also showed superior area under the curve (AUC) for predicting C1q positive results in sera diluted 1:16 than in undiluted sera (AUC = 0.99 vs 0.82). Low MFI by conventional SAB testing in alleles with high C1q MFI increased upon dilution or heat-treating sera and correlated with C1q results. Clinically, in 13 recipients C1q DSA predicted CDC-XM positivity and early AMR (positive predictive value (PV) 87.5 % ; negative PV 100 % ).
In conclusion, SAB titer correlated with and predicted C1q reactivity. The risk for positive crossmatch and early AMR in sensitized heart recipients strongly correlated with C1q binding DSA.