Preventing Floaters

We may never be able to completely rid ourselves of extraneous tissue, commonly known as floaters, in the lab, but we can take steps to understand where it comes from, and how we can prevent it.

Main sources of floaters include, the grossing bench, the embedding stations, and the microtomy stations. At each station, cleaning is an important factor in prevention of floaters. If you don’t clean the forceps between each and every specimen, you can get fragments of tissue that carry from one specimen to the next. Similarly, if forceps are not cleaned between cassettes, tissue can get carried from one block to the next. You also need to be mindful of the wells the forceps are stored in and ensure regular cleaning of these occurs. At the microtomy station, ribbon fragments can get picked up if you’re not cleaning the water bath surface between blocks. Cleaning! Cleaning! Cleaning! It really is super important.

DNA testing and barcoding systems, that provide a timeline for when specimens are at which station, have given proof to this theory, that the majority of floaters are coming from grossing and embedding stations. Though these are the most common causes, other studies, such as one published in the Journal of Histotechnology in 2013, have addressed other possible sources such as batch H&E stainers, showing tissue transfer between slides at this point. (1)

Where floaters become a problem, and where identity testing is used to address them, is in cases where the floaters may result in inaccurate diagnosis, for example when the extraneous tissue is cancerous and not matching the rest of the section. In the interest of maintaining high standards of patient care, and avoiding misdiagnosis, floaters should be prevented. Besides, the cleaning that reduces the frequency of floaters is, in and of itself a best practice.

You will want to address the factors impacting floaters, including cleaning, in your operating procedures, and ensure that everyone in your lab is trained on them. You also want to make sure everyone in your lab is mindful and using common sense practices, such as not putting your fingers in the water bath or touching the slide in parts other than the sides. Wearing gloves, though a controversial practice (we’ve touched on this in several other blog posts), can also reduce the likelihood of your own cells becoming extraneous tissue.

Thank you to Clifford Chapman, Tim Morken, and Gayle Callis for their insight on this topic, shared on The Block, NSH’s member community. You can find answers to common troubleshooting questions like this anytime using the Block’s Discussion Forum.

For more information about floaters, including the study mentioned in this post, check out these articles below in the Journal of Histotechnology, free to members online.


1. Cahill A, Pearson J. Measurement of stainer bath contamination and evaluation of common mitigation strategies. J Histotechnol. 2013: 35(3):130-139.

2. Dimenstein I. "Gadgets for "floaters" prevention in the histopathology laboratory", J Histotechnol. 2011; 34(2):88-90

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