Instant confocal histology for the evaluation of kidney transplant procurement biopsies

Prognostic outcome models might help to minimise the discard rates of renal transplants from deceased donors. To this end, we published 2-Step Scores for both delayed graft function and transplant loss with optional histology. With conventional paraffin PAS histology taking at least 3 h excluding transport time, we tested whether fast, mobile confocal histology with portable VivaScope® 2500 systems might offer a viable and more rapid alternative. After omitting 17 biopsies with less than 12 glomeruli and 1 artery, we collected 14 0-h and 16 renal transplant indication (Tx) biopsies for a combined cohort. All biopsies were scanned in less than 10 min with a VivaScope® 2500, rendering pseudo-HE images, and then underwent our regular paraffin work-up. Banff Lesion Scores ct and cv were assessed on the granular ordinal scale and binary as (ct ≤ 1 vs. ct ≥ 2 and cv ≤ 2 vs. cv3) together with the number of glomeruli as used in the previously published 2-Step Scores in a blinded fashion by an expert nephropathologist on the paraffin sections (P) and VivaScope® 2500 scans (V). Additionally, we examined the ratio of globally sclerotic glomeruli. Correlation and mixed effects linear regressions, as well as Fleiss' kappa statistics, comparing P and V on the combined cohort were applied, supplemented with Bland-Altman statistics providing limits of agreement. Between P and V, granular Banff ct correlated with a kappa of 0.513 (p = 8.38e-05) and a Kendall's W of 0.706 (p = 0.0694) on the combined cohort; binary Banff ct correlated with a kappa of 0.869 (p = 1.92e-06). We had to exclude two more biopsies in which no artery was found in the scanning plane in V. Granular Banff cv correlated with a kappa of 0.109 (p = 0.345) and a W of 0.677 (p = 0.103) between P and V on the combined cohort and binary Banff cv with a kappa of 0.24 (p = 0.204). The total number of glomeruli correlated between P and V with an R of 0.75 (p = 2.3e-06), the number of globally sclerotic glomeruli with an R of 0.82 (p = 4.1e-08), and the ratio thereof with an R of 0.86 (p = 8.6e-10). Instant, decentralised VivaScope® 2500 histology might deliver Banff ct and the number of glomeruli with sufficient accuracy for the 2-Step Scores to predict the risk of delayed graft function and 1-year death-censored transplant loss in deceased heart-beating donors. In contrast, VivaScope® 2500 assessment of Banff cv might not be accurate enough for use in 2-Step Scores.