Biopsies are usually assessed under dissection microscope in a drop of normal saline.
Glomeruli appear as small red spheres in the cortex. The medulla appears as linear stripes. 1,4 Small yellow balls of fat will also be present. 2
Excellent illustrations are available in references 1 and 4.
Guidelines for division of the specimen will vary with the type of biopsy, the clinical question being asked, the urgency of that question, and the approach to subsequent investigations taken in the individual laboratory.3
Native biopsies usually need to be divided into three and submitted for light microscopy, immunofluorescence (IF) and electron microscopy (EM).1,4
A useful diagram provided is in reference 4.
In theory a minimum of one glomerulus per study is usually adequate for IF and EM and the majority should be submitted for light microscopy.1 If the specimen is limited, division is guided by the clinical question and/or immunohistochemistry facilities of the individual laboratory.
When minimal tissue is available, it may be possible to retrieve a few more glomeruli for EM by rinsing out the biopsy needle.1
Renal transplant biopsies may not require electron microscopy and immunofluorescence unless glomerular disease is suspected. 3 However it is important not to transfer the entire specimen to formalin until exact requirements are established.
It is best to dissect the tissue while it is fresh. The majority of the biopsy should be processed for light microscopy but check if samples are required for immunofluorescence and electron microscopy.3
The size of segments for each process will be dependent on the overall size of the core but 3 mm for light microscopy, 3 mm for immunofluorescence & 1 mm for electron microscopy should suffice if there is cortex with at least one glomerulus present in each piece.1 Some medullary tissue for the demonstration of casts in immunofluorescence may be useful if possible.2
One recommendation is to submit 50% of core tissue for light microscopy, 30% for immunofluorescence and 20% for electron microscopy. More tissue from wedge biopsies may be submitted for light microscopy (up to 75% of tissue).5
Wooden sticks may be used (in preference to forceps) to gently lift the cores without crushing.2,4 Renal biopsies must be carefully handled with clean instruments and separated into different solutions without any cross-over contamination of fixatives.2,4
Transfer one piece of tissue into each of the following:
- Viral transport solution or freezing for immunofluorescence
- Glutaraldehyde for electron microscopy
- Formalin for light microscopy