Apolipoprotein A‐Ib as a biomarker of focal segmental glomerulosclerosis recurrence after kidney transplantation: diagnostic performance and assessment of its prognostic value – a multi‐centre cohort study

Summary Recurrence of idiopathic focal segmental glomerulosclerosis (FSGS) is a serious complication after kidney transplantation. FSGS relapse is suspected by a sudden increase in proteinuria but there is not an accurate noninvasive diagnostic tool to confirm this entity or to detect patients at risk. We aimed to validate the diagnostic performance of ApoA‐Ib to detect FSGS relapses by measuring urinary ApoA‐Ib in a retrospective cohort of 61 kidney transplanted patients (37 FSGS and 24 non‐FSGS). In addition, to assess the ApoA‐Ib predictive ability, ApoA‐Ib was measured periodically in a prospective cohort of 13 idiopathic FSGS patients who were followed during 1 year after transplantation. ApoA‐Ib had a sensitivity of 93.3% and a specificity of 90.9% to diagnose FSGS relapses, with a high negative predictive value (95.2%), confirming our previous results. In the prospective cohort, ApoA‐Ib predated the recurrence in four of five episodes observed. In the nonrelapsing group (n = 9), ApoA‐Ib was negative in 37 of 38 samples. ApoA‐Ib has the potential to be a good diagnostic biomarker of FSGS relapses, providing a confident criterion to exclude false positives even in the presence of high proteinuria. It has also the potential to detect patients at risk of relapse, even before transplantation.