Genital Smear – Microscopy
Consistent with O. Reg. 671/92 of the French Language Services Act, laboratory testing information on this page is only available in English because it is scientific or technical in nature and is for use only by qualified health care providers and not by members of the public.
Background
This page provides information about examination of Gram-stained genital smears at Public Health Ontario (PHO). Such examination is a rapid diagnostic method used to investigate suspected cases of bacterial vaginosis (BV), yeast infections, urethritis, and vaginitis.
For information regarding other testing options, refer to the following PHO webpages:
- Identification and Susceptibility Testing for Gonococci: Neisseria gonorrhoeae – Culture, Reference Identification and Susceptibility
- Molecular Detection of Chlamydia trachomatis and Neisseria gonorrhoeae directly from a specimen: Chlamydia trachomatis/Neisseria gonorrhoeae (CT/NG) – Nucleic Acid Amplification Testing (NAAT)
- Identification of Yeast Isolates: Mycology – Reference Identification of Yeast, Filamentous Fungi and Nocardia/Aerobic Actinomycetes
Updates
- The title of this page has been updated from Slide Examination – Genital Smear to Genital Smear – Microscopy.
- Guidelines for completing the requisition form and properly labeling slides and slide holders prior to submission to Public Health Ontario (PHO) have been clarified. Please refer to Submission and Collection Notes 1 & 2 for detailed instructions.
- New contents added:
- Testing indication and limitations to clarify appropriate use and limitations of the test.
- Algorithm and result interpretation
Testing Indications
A genital smear for Gram stain is indicated for patients who present with symptoms that are compatible with bacterial vaginosis (BV), or yeast, Neisseria gonorrhoeae (NG) or Trichomonas vaginalis (TV) infections. Symptoms may include:
- Urethral or vaginal discharge1, 2. In symptomatic males, a urethral Gram stain has a sensitivity and specificity of 95% for detecting Gram-negative diplococci (GNDC), which is indicative of gonorrhea.1
- Dysuria1, 2
- Genital irritation or itching1, 2
- Pelvic pain or discomfort1, 2
- Visible genital lesions or ulcers1, 2
Nucleic acid amplification testing (NAAT) is the recommended method for Neisseria gonorrhoeae (NG) testing. Consider submitting a specimen for CT/NG NAAT, and NG culture, if indicated.
Acceptance/Rejection Criteria
- Only vaginal and male urethral smears on properly labeled slides are accepted.
- Swabs are not accepted for this test. PHO does not prepare smears from swabs.
- Broken, chipped, unlabeled, and incorrectly labelled slides will be rejected and not tested.
Specimen Requirements
| Test Requested | Required Requisition(s) | Specimen Type | Minimum Volume | Collection Kit |
Smear/Gram Stain: Bacterial vaginosis (BV) and/or Trichomonas vaginalis and/or yeast |
Vaginal Smear |
N/A |
Slide Mailer |
|
Smear/Gram Stain: Neisseria gonorrhoeae and/or Trichomonas vaginalis and/or yeast |
Male Urethral Smear |
N/A |
Slide Mailer |
Submission and Collection Notes
Complete all fields of the requisition, including:
- Test(s) requests and indications for testing
- Specimen source
- Patient age and sex or gender including if the patient is transgender (e.g. transfemale or transmale) must be indicated to determine appropriate testing and interpretation.
Label the frosted end of the slide with the patient’s first and last name (or initials), specimen source (e.g. urethral or vaginal), date of collection, and one other unique identifier such as the patient’s date of birth or Health Card Number.
The labeled slide must be placed inside a slide holder, which should be labeled with, at a minimum, the patient’s first and last name, date of collection, and another unique identifier.
Failure to label both the slide and the slide holder may result in rejection or delays in testing.
For additional information see: Criteria for Acceptance of Patient Specimens. See images below for acceptable and not acceptable labelling. Slides that are not correctly labelled will be rejected.
The PHO GC kit/Neisseria gonorrhoeae culture kit (kit order # 390051) is sent with slides and swabs for preparing slide examinations if required.
Follow the instructions for specimen collection found in the GC-Neisseria gonorrhoeae culture kit Instruction Sheet. Make a thin smear by rolling the swab on the slide. Submit only the slide.
Timing of Specimen Collection
Specimens should be collected outside the menstruation period.
Limitations
- Interpretation of vaginal smears for BV from pre-pubertal and post-menopausal individuals may be unreliable due to altered flora; results should be correlated with clinical findings.
- For transgender individuals, the use of Nugent score for interpreting BV has not been validated.
- Microscopy has poor sensitivity for the detection of Trichomonas vaginalis. A negative result does not rule out infection.
Storage and Transport
Allow the smear on a slide to air dry before packaging. Place the slide inside a slide mailer. If needed, secure the slide mailer with an elastic band to prevent accidental opening. Submit the specimen to Public Health Ontario (PHO) as soon as possible. If immediate submission is not possible, store the slides at room temperature (20-25 °C). Do not refrigerate or freeze the slides. Avoid exposing the slides to extreme heat, cold or moisture as these conditions may compromise the integrity of the smear. All clinical specimens must be shipped in accordance to the Transportation of Dangerous Good Act.
Test Frequency and Turnaround Time (TAT)
Slide examination for genital smears is performed daily, Monday to Friday at Public Health Ontario’s laboratory -Toronto, Ottawa and Sault Ste. Marie locations.
Turnaround time is up to 4 days from receipt at PHO.
Genital smears are fixed and stained by the Gram staining method. Stained smears are examined microscopically. The Nugent Score is used to assess BV in vaginal smears.
Algorithm
|
Specimen Source |
Slide Examination |
|---|---|
|
Vaginal smear from an individual <12 years old |
Routine examination for yeast and pus cells. TV and BV by request only. |
|
Vaginal smear from an individual >12 years old |
Routine examination for BV, TV, yeast, pus cells. |
|
Male urethral smear |
Routine examination for GNDC and pus cells. TV and yeast by request only. |
Interpretation
For Vaginal Smears:
| Examination |
Result |
Comments |
|---|---|---|
|
Pus cells |
Present or Not Present |
|
|
Yeast |
Present or Not Present |
|
|
Trichomonas vaginalis |
Present or Not Present |
If present, will be reported even if not specifically requested. Microscopy has poor sensitivity for the detection of Trichomonas vaginalis. A negative result does not rule out infection. |
|
Bacterial vaginosis |
Nugent score of 0-3: Gram-stained smear is NOT consistent with bacterial vaginosis Nugent score of 4-6: Gram-stained smear shows altered vaginal flora but is NOT consistent with bacterial vaginosis Nugent score of 7-10: Gram-stained smear is consistent with bacterial vaginosis |
For individuals <12 years old, BV is only reported if requested on the requisition. The Nugent Score for BV has not been validated for pre-pubescent and post-menopausal women or transgender individuals. Interpret results with the patient’s symptoms and clinical history. |
For Urethral Smears:
| Examination |
Result |
Comments |
|---|---|---|
|
Gram-negative diplococci |
Present or Not Present |
Indicative of Neisseria gonorrhoeae. If not already done, consider submitting a specimen for CT/NG NAAT or NG culture. Refer to the CT/NG NAAT test information sheet for acceptable specimen types for NAAT. In rare cases, the presence of GNDC on a urethral smear may represent urethritis caused by Neisseria meningitidis. If GNDC is present and a concurrent specimen tested negative for NG by NAAT, consider submitting a urethral swab for culture to determine Neisseria species. |
|
Pus cells |
Present or Not Present |
|
|
Yeast |
Present or Not Present |
If present, will be reported even if not specifically requested. |
|
Trichomonas vaginalis |
Present or Not Present |
If present, will be reported even if not specifically requested. Microscopy has poor sensitivity for the detection of Trichomonas vaginalis. A negative result does not rule out infection. |
Reporting
Results are reported to the physician, authorized health care provider (General O. Reg 45/22, s.18) or submitter as indicated on the requisition.
Urethral smears that are positive for GNDC are reported to the Medical Officer of Health as per the Health Protection and Promotion Act.
References
- Public Health Agency of Canada. Gonorrhoea guide: screening and diagnostic testing. Available from: Gonorrhea guide: Screening and diagnostic testing [Accessed 10 September 2025]
- Public Health Agency of Canada. Sexually transmitted and blood-borne infections: Guides for health professionals. Available from: Sexually transmitted and blood-borne infections: Guides for health professionals [Accessed 10 September 2025]
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