As a common procedure, the renal needle biopsy, especially of a native kidney, requires triage of the obtained specimen for conventional light microscopy (LM), electron microscopy (EM) and immunofluorescence (IF) studies (1, 2). Although the concrete technical details might be different depending on the institution, there are general principles of a needle renal biopsy triage. Here are some practical tips for the fast and efficient division of the specimen.
The division procedure requires two small forceps (the forceps should be distinguishable from each other), two disposable blades 10 (better than 22), two glass slides. The reason for double instruments is to prevent artifacts in immunofluorescence studies. The dissecting microscope is adequate in the evaluation of the fresh material when the glomeruli are definitely visible, but if the specimen was fixed, the glomeruli, especially with some degree of sclerosis, sometimes barely distinguishable. A regular microscope is a better option.
The tactic of the division procedure
The tactic of the renal needle biopsy division depends on three conditions:
the indication for the biopsy, the type of fixation, the amount of the biopsy material.
Indication for biopsy
The renal biopsy is done for four main purposes: on native kidneys for the diagnosis of acute renal failure or chronic disease/tumor and allografts for transplant rejection or pathology in the transplanted kidney. The clinical question determines the type of examination and the selection of samples, especially if the material is limited. For example, if the biopsy is taken to diagnose an acute rejection or acute renal failure, the best obtained material goes for the light microscopy, but if the reason for biopsy is possible Lupus erythematosus the IF and EM have the preference.
Ideally the specimen should be delivered to the pathology in fresh state. Some clinicians assume this too literally sending the cores on a napkin, sometimes dry out. The clinicians should be aware that the laboratory cannot for some reasons process the specimen immediately and the saline solution is the best option. Some facilities practice a protocol when the laboratory participates in assessment of adequacy of the obtained material.
As a common practice, the specimen is placed for light microscopy in 10% formalin, for electron microscopy in 2.5% glutaraldehyde. Ideally, the specimen’s part intended to be for immunofluorescence should be immediately frozen but by established practice it is often placed in Zeus (Michel) solution. Of course, this is the only option if the specimen is sent to an outside institution.
If glutaraldehyde and formalin are, in general, interchangeable, the Zeus solution cannot be mixed with others. Black sediment develops if Zeus solution is mixed with glutaraldehyde. With some losses, especially in EM studies, the specimen from Zeus solution can be transferred in formalin or glutaraladegade but not otherwise. This is the reason why the duel set of instruments is necessary.
Amount of the renal biopsy material and its division
Usually an 18-gauge needle is used for the biopsy. The use of a 24-gauge needle is undesirable due to too thin core that has not enough informative material and is difficult to handle. When the amount of the obtained biopsy is abundant and the cortex has many glomeruli, the division is simple. According to the commonly accepted standard, for example, 10 mm of the cortex is divided 1-2 mm for EM, 2- 3 mm for IF and the rest goes for light microscopy.
The problem appears when the informative material is limited. There is an unfortunate mode by the outside institutions to divide obtained cores of renal biopsies by blindly cutting tips of the core and placing small fragments of 1mm or less in glutaraldehyde for EM assuming that only a few glomeruli are required for examination. However, there is no any guarantee that the small fragments have the informative material. Some of few available glomeruli might be damaged while cutting small fragment. When there is scarce material, in my opinion, it should be divided only between glutaraldehyde and Zeus solution. The institution that specializes in kidney biopsies does the triage anyway.
If the informative material is found only in Zeus solution, the part indented for EM should be placed in a vial with the Wash Solution from the Zeus kit. The washing would be useful for LM material either.
The triage procedure
This is a description of my personal performance of renal biopsy triage. There are numerous variants in the concrete cases, but the principles remain common.
If the specimen comes in fresh state the division is simple: the first sample is taken for IF (a snap freeze in isopentane or transfer in the Zeus solution), the second sample is placed in glutaraldehyde for EM, the rest goes for light microscopy. The specimen in saline solution has a priority in processing to minimize the autolysis.
If the specimen comes from the outside institution, I always start with glutaraldehyde vial. All material is placed on a glass slide. The core with the most representative glomeruli is chosen under the low magnification. The #10 blade cuts 2-3 mm core. Although theoretically only one glomerulus is necessary for examination, the more the better rule applies in this situation. Even glomeruli on the side of the core might be valuable. On the other hand, uninformative fragments for EM should not be included in the sample. This material is left for LM.
The second is examined the formalin vial. The material can go also for EM if the material in the glutaraldehyde vial is less representative.
The third is examined the Zeus solution vial using a different forceps, blade and glass slide. The adequacy of the material for IF is evaluated. The extra material is taken out if it can contribute to EM (in the case, if it was not enough informative material in glutaraldehyde) or LM without compromising IF examination. A preliminary washing off the Zeus solution is desirable. The latter process is time consuming and not always can be carried out in practice.
In general, everything left from EM and IF goes to LM even fat because the latter can also have a diagnostic value, for example reflecting paranephritis. Even blood or other tissue might have an informative value.
There are numerous variants of division due to unpredictable variety of the biopsy material but it is possible to select the informative samples in the most cases. Sometimes the triage process is fast and effective, sometimes cumbersome and frustrating.
Howie A. – Handbook of Renal Biopsy Pathology. Kluwer Academic Publishers, 2002: 10 – 6.
- Furness PN. Renal biopsy specimens. J Clin Pathol 2000; 53: 433-438