Tissue Sampling
Key Aspects
Needle or wedge biopsy tissue should be processed immediately after excision. Never allow the tissue to dry out. If there is any delay, keep the tissue on saline-moistened gauze. Do not use IF Transport Medium or any other fixative as a holding solution prior to partitioning the sample.
Examining needle biopsy tissue with a 10X to 15X hand lens or dissecting microscope may be useful in distinguishing adipose (clusters of fat droplets) and skeletal muscle (darker color and easily disrupted into fascicles when prodded) from renal tissue. Sometimes, renal tissue can be differentiated with magnification as either cortical (punctate glomerular blushes or raised hemispheres) or medullary (vascular striations).
Appropriation of tissue for light, immunofluorescence (IF) and electron microscopy (EM) may vary according to the amount of tissue available, and the clinical differential diagnosis. For evaluation of glomerulopathies, cortical tissue is required and can sometimes be identified by magnification or can be assumed to be present in the most proximal (superficial) part of the needle core. Of note: only a small segment of cortex (approximately 3mm) is required for EM analysis. We recommend using 15 gauge biopsy needles and to obtain 2 or 3 long cores. The use of 18 gauge needles often results in inadequate tissue samples.
Tissue for the three methods of examination can be obtained in a number of ways: 1. three separate cores, one for each procedure; or 2. two cores, one for light microscopy, small segments from both ends of the other for electron microscopy and the remainder for immunofluorescence microscopy. For renal transplant biopsies, 2 cores are recommended for light microscopy, and one smaller core for IF. Allograft biopsy tissue in glutaraldehyde for EM studies is only required a) if a glomerular disease is suspected or b) > 1 year post transplantation.
If very limited tissue is available, more than one procedure can be performed on tissue optimally prepared for one method of study, e.g.: 1. tissue submitted in transport medium for immunofluorescence microscopy can also be processed for light and electron microscopy (this introduces technical artifacts), or 2. tissue fixed in formalin for light microscopy can also be processed for EM. For suspected glomerular diseases, if there is only one small piece of tissue, it is usually best to submit all of the tissue in IF Transport Medium.
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