Coverslipping Part 1: Introduction and Limitations

By: Nuria Bosch, Lucas Pena, Jaime Augusti, Federica Melone, Carmelo Lupo, Samuel Caboni, Paolo Locatelli; Pathology Department, Diapath

Introduction to Coverslipping

Histological and cytological sections, which need to be examined for any length of time or stored, must be mounted under a cover-slip [3]

A drop of synthetic mounting medium is placed over the tissue after blotting away excess clearing solution, and a glass coverslip is attached. The steps sound simple enough, but they actually require some technical finesse [1]. In recent years, automatic coverslipping machines have been marketed by several firms. These are attractive because they potentiality save technologists expenditure of time in a rote procedure. However, our experience with such devices has been less than satisfactory. Quite often, the amount of mounting medium dispensed is inadequate, and air bubbles rapidly appear under the coverslips after the slides are delivered to the pathologist [1]

Limitations of Current Coverslipping Methods

  • Various laboratories use synthetic adhesives to glue sections and small specimens on the microscopic slides. This can pose a problem, depending on the RI, permanency, pH, and chemical components of the glue or mountant, as there is the potential to erode or destroy the specimen [3].

  • Thick samples, such as traditional cytology pap smears, are difficult to cover without bubbles.

  • It often happens that the coverslip is misaligned. This situation, in addition to the already mentioned possibility of the presence of bubbles, cause the block of the digital scanner and the impossibility of obtaining digital images of the slide.

  • It can take a long time to remove coverglass from a slide: in some cases, you need to soak the slide in xylene for several days. [6]

  • When the ratio of xylene to medium is incorrect, or if there is too much xylene in the mounting medium, then high power focusing does not project crisp cellular detail and the mounting media will retract from the tissue as drying occurs and it will become sticky from excess mounting medium [2]

  • Errors of identification of the right side of the slide can take place. 98.5% of the errors in AP labs are due to lack of attention and oversight and only 1.5% appeared to be due to a lack of knowledge of the process. [5]

In part two of this series, the Diapath Pathology Department will share their research comparing traditional coverslipping methods to liquid glass coverslipping, which they presented as a poster at the 2018 NSH Annual Symposium/Convention. Stay tuned!


1. Mark R, Wick MD, Diagnostic Histochemistry , 11–12 (2008).

2. Carson L, Cappellano CH, Histotechnology, a Self Instructional Text , 71(2015).

3. Ravikumar S, Surekha R, Thavarajah R. “Mounting media: An overview”. J NTR Univ Health Science, 2014;3, Suppl S1:1-8

4. Brown PA. “ A review of technique used in the preparation, curation, and conservation of microscope slides at the natural history museum London ”. The Biology Curator 1997; 10:1 33

5. Morelli P,et al.Analysis of errors in histology by root cause analysis: a pilot study” J Prev Med Hyg. 2013; 54(2):

6. Ellys P, “ Problems in Histopathological Technique . IHCWORLD 2002. Problem 30.Web.

7. Guin JP et al., “Plasticity at nanoindentation site in glass :a possible experimental benchmark for numerical modeling” 22ème Congrès Français de Mécanique (2015)

8. David M et al., “ Pathology Economic Model Tool “A Novel Approach to Workflow and Budget Cost Analysis in an Anatomic Pathology Laboratory” Arch Pathol Lab Med—Vol 134, 2010

9. Lang EV et al., “Large-Core Breast Biopsy: Abnormal Salivary cortisol profiles associated with uncertainly of diagnosis” Radiology 2009, 250(3)

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