Written and maintained by CASRAI Editorial Board
Last updated
This page describes products and general use; it is not medical advice.
A microscope slide label is the identifier attached to or written on a slide so the specimen on it can be traced back to its source. Anyone who handles slides, from histology staff to research technicians to the people who stock a lab, can use this page to tell the main label types apart, see what a pathology guideline says a slide label should identify, and understand why printed labels need solvent-resistant materials.
What a microscope slide label is
A slide label links a piece of glass to a case, a patient or a sample. It can be handwritten on the frosted end of a slide, or it can be a separate label, often printed, that is attached to the slide. The slide itself is explained in what a microscope slide is, which notes that the frosted area of a slide accepts pencil, pen or printed labels, making slides easier to identify and track.
Labels matter because slides pass through several steps. In tissue work, sections are cut (see microtomes and cryosectioning), then stained (see histological staining) and coverslipped (see coverslips). A label that fades or lifts during any of those steps leaves a specimen that cannot be matched to its source.
Types of microscope slide labels
Three kinds of identification are in common use. They differ in how the information gets onto the slide and what the identification has to withstand.
| Type | Typical use | Key difference | Source |
|---|---|---|---|
| Frosted end of the slide | Identifying a slide by writing or printing directly on its frosted area | Part of the slide itself; accepts pencil, pen or printed labels | CASRAI, what is a microscope slide |
| Thermal-transfer printed, solvent-resistant slide label | Slides that go through staining and processing, including automated slide processors | Printed with a thermal-transfer printer; resistance to xylene, toluene, hexanes, alcohols and acetone depends on printing with a solvent-resistant ribbon | Labtag, xylene and chemical resistant labels |
| Blackout label | Re-identifying slides that were marked with unclear, inaccurate or missing information | Removable cover-up label that conceals existing information and is printed with a xylene-resistant resin ribbon | Labtag, xylene and chemical resistant labels |
Who uses them: histology and pathology laboratories, research laboratories that section tissue, and teaching laboratories that keep slide sets.
What should a slide label identify?
For surgical pathology, the College of American Pathologists (CAP) publishes the guideline Uniform Labeling of Blocks and Slides in Surgical Pathology (CAP with the National Society for Histotechnology). It states that laboratories should ensure that all blocks and slides are clearly labeled using two patient identifiers. The points below are drawn from the CAP guideline and its published questions and answers.
- Two identifiers. Every block and slide carries two patient identifiers. Where no accession number has been assigned yet, CAP says blocks and slides should carry at least two patient identifiers, one of which is the patient name.
- Accession designation. The designation on the report and on all related blocks and slides should include the case type, the year and a unique accession number.
- Cutting order. When several slides are cut from a single block, label each slide in the order of cutting.
- Stain or procedure name. The guideline states that clear identification of the stain or procedure name on the slide label is essential.
This is a guideline for surgical pathology, which is a specific clinical setting. Research and teaching laboratories set their own labeling rules, and nothing here replaces a laboratory’s own procedures or its accrediting body’s requirements.
Do slide labels need to resist solvents and stains?
Yes, when slides go through processing. Staining and clearing use solvents, and a label that smears or dissolves defeats its purpose. The manufacturer Labtag describes its thermal-transfer printable slide labels as suitable for use in automated slide processors and as resistant to xylene, toluene, hexanes, alcohols and acetone when printed with solvent-resistant ribbons. It also lists resistance to newer non-toxic xylene substitutes and describes the labels as particularly resistant to histological stains such as eosin Y and hematoxylin.
The detail worth noticing is that the resistance is a property of the label and the ribbon together. The manufacturer states that chemical resistance requires printing with a solvent- or xylene-resistant ribbon, so a resistant label stock printed with an ordinary ribbon is not the same product.
How to choose a label
Three criteria apply.
- Match the label to the processing. If slides are run through automated slide processors or solvents, use a label the manufacturer states is suitable for those conditions and print it as the manufacturer specifies, including the ribbon type.
- Match the content to the rule you work under. In surgical pathology, the CAP guideline calls for two patient identifiers, an accession designation with case type, year and unique number, order of cutting, and the stain or procedure name.
- Know the options for an unclear slide. The manufacturer describes removable blackout labels for re-identifying slides marked with unclear, inaccurate or lacking information.
Common mistakes
- Labeling with a single identifier when the applicable guideline calls for two.
- Leaving the stain or procedure name off the label.
- Printing a solvent-resistant label stock with a ribbon that is not solvent resistant.
- Labeling multiple slides cut from one block without recording their cutting order.
FAQ
Where do you put the label on a microscope slide?
Slides with a frosted end are made to take pencil, pen or printed labels there, which keeps the label clear of the specimen area. Separate printed labels are also used, as described above.
How many identifiers should a pathology slide carry?
The CAP guideline says all blocks and slides should be clearly labeled using two patient identifiers. If no accession number exists yet, at least two patient identifiers are used, one of them the patient name.
Can a slide label survive xylene and alcohols?
One manufacturer states its thermal-transfer slide labels resist xylene, toluene, hexanes, alcohols and acetone when printed with solvent-resistant ribbon. Without that ribbon, the claim does not apply.
What is a blackout label?
According to its manufacturer Labtag, a removable cover-up label that conceals existing information on a flat surface such as a glass slide, used to re-identify slides marked with unclear, inaccurate or lacking information.
Sources
- College of American Pathologists, Uniform Labeling of Blocks and Slides in Surgical Pathology, checked 31 October 2026.
- Labtag, Xylene and Chemical Resistant Labels (manufacturer product page), checked 31 October 2026.
- CASRAI, What is a microscope slide?, checked 31 October 2026.
