Filtration Kit for Surgical Pathology

Rationale (partially presented in “Filtration in Surgical Pathology” link Grossing Techniques and in “The Diaper Pad for Filtration” link Equipment, Instruments & Gadgets,)

Completeness of specimen submission, especially in biopsies, is the obligatory prerequisite of processing in surgical pathology. It must not be damaged in any way, and, of course, the biopsy ought to be processed as quickly as possible. Often the biopsy specimen contains numerous fragments that require a cumbersome transfer to the processing cassette. The mucus in biopsy specimens presents still another problem. Sometimes the specimen’s parts are almost invisible or extremely fragile. The best answer to these problems is filtration.

Filtration directly into the cassette through the lens paper like material is the safest and fastest method. The main determining factor for the method of filtration is the amount of the fluid in the specimen’s container. A moderate amount of the container’s content (the majority in general practice) requires a method, or a “trick” that enhances filtration by absorbing the fluid.

A piece of a diaper can be an absorbing material. Baby and other diapers are very much ubiquitous.

Here is a short remainder of a disposable diaper design in regard to filtration. The acquisition layer of a diaper works like blotting paper, while the core of a diaper includes granular super-absorbent hydrophilic polymer. Water becomes slightly gelled when passed through the acquisition layer unraveling the polymer net. The polymer transforms in numerous swollen granules like white caviar. The wet polymer core works as “a pump” soaking water from the filtration surface. The diaper becomes engorged slowly.

Filtration kit

A super adsorbent hydrophilic polymer (sodium polyacrylate with sodium carbooxalate group) rectangular 2x 2” pad is combined in a kit with 10 porous 1 x ½ “papers. The pad is similar to a diaper for collecting fluid, for example a regular baby diaper. The brand of the diaper does not matter substantially. The pad is loosely sealed to allow the fluids to engorge it by expanding granules of the adsorbent polymer.

Fig.1.  A cassette with filtration paper inside. The cassette is mounted on the engorged diaper pad.

The diaper pad is not only an enhancer of fluid, but also a convenient platform for filtration manipulations.

The kit is designated for filtration biopsies directly in the histology processing cassette. The pad is placed with the acquisition layer up in a box, for example, a histology glass slides. The wet porous filtration paper is placed in the processing cassette that is mounted on the wet diaper pad. The content of the specimen’s container is gradually poured for filtration onto the paper in the cassette. The acquisition layer of the pad enhances filtration due to capillarity forces while the polymer absorbs the fluid. One kit can be used for 5-10 containers depending on the amount of fluid (20 to 50 ml).

As the filtration porous papers, the best is the internal layer of Kimberly-Clark TECNOL FLUIDSHIELD mask that has large spaces between the fabric threads for permeability.

During my experimentation with lens papers, I found that “improvements” in their manufacturing have led to decrease of their permeability (I could definitely see under the microscope the different structure of the threads). Then again during my experimentation with protective masks, I dissected (literally) many surgical masks, including the Kimberly-Clark TECNOL FLUIDSCHIELD. I found the internal layer of the latter (one of four) is optimal as a filtration paper.


Kimberly- Clark TECNOL FLUIDSSHIELD mask

The fourth internal level of the mask

Permeability for filtration biopsies

The excellent permeability of the paper is indispensable for filtration of bone marrow aspirates.

The used diaper pad is disposed with other gross room soiled formalin soaked materials according to local regulations.


The Technical Note in “Journal of Histotechnology” (2006; v.29, No. 3, p. 204) presents the concept of filtration in surgical pathology as well as details of the practical application of methods of filtration, including direct filtration in the histology cassette by using a diaper like pad.

This kit can replace all other devices and gadgets for filtration, including for very small or amorphous specimens. The universality of the method is the main advantage. The porous filtration paper is convenient to handle during embedding after paraffin impregnation.

Filtration directly into a cassette can eventually be the standard procedure of small biopsies processing. This method enhances faster processing of a biopsy if there are many fragments, without or with minimal use of instruments, thus preventing damage and contamination. The main advantage is the complete submission of the specimen.

This gadget proposal is posted for everyone who wants to use it in laboratory practice or able to commercialize it in a product for the sake of improvement biopsy grossing technology.


3 Responses to Filtration Kit for Surgical Pathology

  1. Rafael A. Parra says:

    Dr: Dimenstein
    What do you recommend to filtrate ECC or any specimen with mucous in order to prevent loss specimen during processing.
    Lately we are having problems with the micro tea bags and filter paper.

    • izakd says:

      I used the internal level of Kimberly-Clark Protective mask. I has a good permeability, convenient in wrapping into envelop before placing into the cassette.

  2. izakd says:

    The wet absorbent diaper like materials is helpful. I used this also for bone marrow aspirates. Sometimes it is necessary to stir the filtrate to make the process faster. I always started with filtration because it takes some time.

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