Use of freeze-drying technology for the study of renal biopsies

Adequate handling of renal biopsies requires processing for light and electron microscopy, as well as for immunohistochemical study. Problems of adequate sampling are frequently encountered, and tissue size can be insufficient, since morphologic examination requires chemical fixation, while immunofluorescence study is currently performed on snap-frozen, cryostat-cut tissue. The application of freeze-drying technology on 20 renal needle biopsies has been investigated to assess the feasibility and reliability of the technique as a routine diagnostic tool in renal pathology. Morphologic as well as immunohistochemical studies were performed on freeze-dried, paraffin-embedded specimens, including immunofluorescence and PAP techniques to detect immunoglobulins, complement fractions, fibrinogen, collagen types, and laminin. Our results showed good preservation of tissue morphology, similar to standard formalin fixation. Moreover, absence of diffusion artifacts and intensity of immunohistochemical reactions were comparable to what is obtained with cryostat sections. We therefore suggest that freeze-drying before paraffin embedding is, at least for diagnostic purposes, preferable to formalin fixation; unfixed, cryostat-cut sections can still be informative and should be used whenever tissue is available in selected cases, and/or in experimental work.