First investigation on microcrystalline pathologies of kidney allografts through cellular scale physicochemical techniques

Tubulo-interstitial microcalcifications in renal transplant are described with a wide difference of incidence (4–78%) according to time and goal of biopsies. Currently, staining procedures are used to deduce the composition of crystals and speculate about their aetiologies. Here we test the contribution of infrared microspectroscopy (IR-MS) in understanding kidney transplant crystal deposits. First, microcalcifications observed in 118 allograft biopsies are studied by IR-MS. The Fourier transform infrared signal shows that a major proportion (92%) of calcium phosphate crystals is in the pure or mixed form. Next, we compare 50 patients with calcifications to 100 without calcifications and show persistent hyperparathyroidism and tubular cell vacuolization as circumstances of crystal deposition. Finally, the graduation level of calcification by IR-MS appears to be correlated with the graft outcome. Graft survival seems to be worse in case of high microcalcification detection by IR-MS. These preliminary data suggest IR-MS as a great tool for clinicians to diagnose, characterize, and quantify microcalcifications in kidney allografts.