Quick facts
- A wet mount is a drop of specimen placed on a glass slide, covered with a coverslip and read by light microscopy while it is still wet.
- The slide and coverslip are laboratory consumables, not named devices, in both countries.
- Where slides or coverslips are promoted for a specific medical use they can be caught by 21 CFR 862.2050, the general-purpose laboratory equipment entry at Class I.
- In Canada a laboratory consumable is a device only where it is intended for a medical purpose; a plain slide is not a device at all.
- A saline mount and a KOH mount answer different questions, and the choice is made before the specimen is placed.
- The entries and rule text below were checked against the current eCFR text and the Regulations on 2026-10-07.
A wet mount is the simplest microscopy preparation in the laboratory: a drop of sample on a slide, a coverslip lowered over it, and a look under the microscope before the preparation dries. It is quick, it needs almost no equipment beyond the microscope, and it is one of the few preparations that has to be read immediately, because motile organisms stop moving as the mount dries. The slide and the coverslip are ordinary consumables in the device rules, but the preparation around them carries the timing and record rules that decide whether a result can be used.
What is a wet mount and when is it read?
The sample is placed on a clean slide, a coverslip is lowered so that it spreads the drop without trapping air, and the slide goes straight to the microscope. Saline keeps organisms alive and motile for the few minutes the mount is useful; a potassium hydroxide mount clears cellular material so that fungal elements are easier to see. The slide is read as soon as it is made, and the result is written down with the time, because the same sample read an hour later will not show the same thing.
| Mount | What is added | What the reader is looking for |
|---|---|---|
| Saline | Isotonic saline | Motile organisms, cells and crystals |
| KOH | Potassium hydroxide | Fungal elements after cells are cleared |
| Iodine | Iodine solution | Stained elements where a stain is wanted |
| Saline plus oil | Immersion oil on the coverslip | Higher magnification detail |
How do Canada and the United States treat slides and coverslips?
Neither country names a microscope slide or a coverslip. Both reach the same place: a plain slide is not a device, and a slide promoted for a medical use can be.
| Item | Canada | United States |
|---|---|---|
| Named entry for a slide or coverslip | None | None |
| Plain slide or coverslip | Not a device | General laboratory supply |
| If promoted for a specific medical use | Assessed against the intended use | 21 CFR 862.2050, Class I |
| Mounting reagent | Assessed by intended use | Reagent entry where it is a medical reagent |
| Basis of the class | Intended use recorded for the product | The use the product is promoted for |
| Records | None for a consumable | None for a consumable |
In the United States the openFDA device classification API lists 21 CFR 862.2050 for general-purpose laboratory equipment labelled or promoted for a specific medical use, with its entries at Class I. A box of slides sold to hold a specimen makes no medical claim, so it stays outside the entry; a slide sold inside a test kit takes on the character of the kit. In Canada the Medical Devices Regulations apply only where a product is intended for a medical purpose, so a plain slide is not a device and needs no device records.
Why is the timing the hard part?
Because the mount is a live preparation. Organisms that move in saline stop moving as the drop dries or cools, and a reader who arrives late sees a still field and cannot tell whether the sample was negative or the mount was old. Fixing the mount with a stain stops the movement but also changes what can be seen. That is why a wet mount is read at the bench, within a stated time of collection, rather than batched with other slides. The record that makes the read usable is the collection time and the read time together.
| Step | Rule of practice | What it protects |
|---|---|---|
| Slide | Clean and free of grease | A greasy slide will not spread the drop evenly |
| Coverslip | Lowered at an angle to avoid air | Air bubbles look like artefacts |
| Volume | A drop that just fills the coverslip | Too much floods; too little dries |
| Time | Read immediately after collection | Motility is lost as the mount ages |
| Record | Collection time and read time | The result is tied to the sample's age |
Which standards cover the preparation?
The practice standards sit with the laboratory rather than the slide. ISO 15189:2022 sets the competence and quality requirements for a medical laboratory, including how a preparation is made, read and recorded. The CLSI standards cover the bench procedures for the organism groups a wet mount is used for, and the WHO Laboratory Biosafety Manual covers the containment practice for reading a live culture or a fresh specimen. The acceptance rules a sample must meet before it is prepared are set by the receiving laboratory, and the Public Health Ontario index and its specimen acceptance criteria set those in Ontario.
| Element | What the standard covers | Why it matters at the bench |
|---|---|---|
| Competence | Who may read a mount, under ISO 15189 | An untrained read is not a result |
| Procedure | The bench method under CLSI | A different method reads a different result |
| Containment | Handling a fresh specimen under the WHO manual | A wet mount is a live preparation |
| Acceptance | The rules in the PHO index | A sample prepared before acceptance may be wasted |
Which consumables does a microscopy bench restock?
A microscopy bench restocks as a set. The sterile graduated 90 mL specimen cups carry the sample to the bench, and the double-tipped cotton swabs are the collection item when the specimen is taken by swab. Where a culture is also set up beside the mount, the sample travels in a second sterile specimen container, and a laboratory that also monitors its own steriliser pairs the sterilization monitoring collection with the 24-hour monitoring five-pack trial. Laboratories and multi-site groups ordering at case level use the wholesale ordering page, and the B2B wholesale collection lists the lines held for institutional buyers. Reselling? become a distributor.
How is the result recorded?
The result is recorded with the specimen source, the collection time, the read time and the mount used, because a wet mount read is only meaningful against the age of the sample. A negative read on an old mount is not the same as a negative read on a fresh one, and a laboratory that keeps only the outcome and not the times cannot defend the result later. That is the reason a one-line bench note is worth more than a memory of the shift: the times are the evidence.
Sources
- 21 CFR 862.2050, General purpose laboratory equipment labelled or promoted for a specific medical use
- openFDA device classification API
- Medical Devices Regulations, SOR/98-282, full text and Schedule 1
- Health Canada, medical devices
- ISO 15189:2022, medical laboratories, requirements for quality and competence
- ISO 13485:2016, medical devices quality management
- ISO 14971:2019, risk management of medical devices
- CLSI, clinical and laboratory standards
- CLSI standards and products
- World Health Organization, laboratory biosafety manual
- World Health Organization, laboratory quality management system
- Public Health Ontario, laboratory services test information index
- Public Health Ontario, specimen acceptance criteria
- College of Medical Laboratory Technologists of Ontario
- Institute for Quality Management in Healthcare
- CCOHS, OSH answers
- Standards Council of Canada
- US FDA, medical devices
Where a microscopy read is recorded
A wet mount read that is not written down cannot be defended later. The printable microscopy bench log is a blank sheet with columns for the specimen, the collection time, the read time, the mount used and the outcome, so a late read is visible on the day rather than remembered later. The bench log generator on the same page sizes the sheet to the number of benches and shifts a laboratory runs. No account and no sign-up are needed to open either one.
Every bench and every mount is different. Ask a compliance specialist and you will get a written answer specific to your equipment and province, with the regulation or standard it is based on cited.
Related reading
- Culture media, differential and selective, in Canada vs the US: which rules
- Specimen acceptance criteria in Canada vs the US: which rules
- Sputum collection containers in Canada vs the US: which rules
CliniEco Medical supplies eye care, laboratory and dental consumables of the kind described in this article. MDEL #35334. This article is written for optometry, laboratory and procurement professionals and is not legal advice; the class of a device and the records kept by a clinic belong to the manufacturer and to the requirements that apply to it.
Frequently Asked Questions
Is a microscope slide a medical device?
No. Neither country names a slide or a coverslip. A plain slide is a laboratory consumable, and in the United States a slide promoted for a specific medical use can be reached by 21 CFR 862.2050 at Class I.
What is the difference between a saline mount and a KOH mount?
A saline mount keeps organisms alive so that motility can be seen. A potassium hydroxide mount clears cellular material so that fungal elements are easier to see. The mount is chosen before the specimen is placed.
Why does a wet mount have to be read immediately?
Because organisms stop moving as the mount dries, and a reader who arrives late cannot tell a negative sample from an old preparation. The collection time and the read time are recorded together for that reason.
How does Canada classify a slide or coverslip?
The Medical Devices Regulations apply only where a product is intended for a medical purpose. A plain slide is not a device and needs no device records, while a slide packaged in a test kit is assessed with the kit.
Which standard covers the preparation?
ISO 15189:2022 covers laboratory competence and quality, the CLSI standards cover the bench procedures, and the WHO Laboratory Biosafety Manual covers containment for a live or fresh specimen.
Can a wet mount replace a culture?
No. A wet mount is a direct look at a fresh specimen and is read at the bench. A culture grows the organism and is used where identification and susceptibility are needed.
Does the coverslip affect the class of the article?
No. The coverslip is a consumable like the slide and is not named as a device in either country.
Where should a microscopy read be recorded?
The printable microscopy bench log at the compliance log centre has columns for the specimen, collection time, read time, mount used and outcome, and the bench log generator on the same page sizes the sheet to the number of benches and shifts a laboratory runs.
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