How to avoid missing the os during a Pap smear?

Avoiding Missing the Cervical Os During Pap Smear Collection

Optimal Collection Technique and Device Selection

To avoid missing the cervical os during Pap smear collection, use the combination of an extended-tip spatula for the ectocervix and transformation zone followed by an endocervical brush for the endocervical canal, as this provides the lowest false-negative rate and ensures adequate sampling of all critical areas. 1

Proper Visualization and Positioning

• Ensure adequate visualization of the cervix by selecting the appropriate speculum size and positioning it to fully expose the cervical os before beginning sample collection 2
• If mucopurulent discharge obscures the os, carefully remove it with a saline-soaked cotton swab before specimen collection to allow proper visualization 2
• Postpone the procedure if heavy menstrual flow prevents adequate visualization, though abnormal bleeding should not delay testing 1, 2

Step-by-Step Collection Technique

For the ectocervix and transformation zone:

• Use an extended-tip spatula (superior to conventional Ayres spatula) and perform circumferential sampling by rotating the spatula 360° around the cervical os 1, 2
• The extended tip must contact the transformation zone adjacent to the external os during the entire rotation 1
• Plastic spatulas are preferred over wooden ones, especially for liquid-based cytology, as cells wash off more readily 1

For the endocervical canal:

• Insert the endocervical brush until the bristles most proximal to the handle are approximately even with the external cervical os 1
• Rotate the brush exactly 180 degrees (one-half turn) in the canal—additional rotation does not improve sampling and may cause bleeding 1
• Use the brush after spatula sampling to avoid obscuring the ectocervical sample with blood 1

Alternative Single-Device Option

• Cervical broom devices can be used as an alternative, simultaneously sampling the ectocervix, transformation zone, and endocervix 1
• Insert the long central bristles into the endocervical os while pressing the broom against the cervix so outer bristles bend 1
• Rotate in one direction only for five complete rotations (not back and forth, as this causes cell loss) 1
• However, research shows the broom alone performs poorly compared to spatula-brush combination, with higher rates of absent endocervical cells (OR = 3.12, P < .001) 3

Special Populations Requiring Modified Technique

Postmenopausal and older women:

• May have atrophic vagina, stenotic cervical os, and inaccessible squamocolumnar junction 1
• Use gentle scraping with wooden or plastic spatula in circular fashion, followed by gentle insertion and rotation of endocervical brush 1
• The endocervical brush is particularly valuable in women with prior cervical treatment (cryotherapy, laser ablation, conization) as it collects more diagnostic material than swabs 1

Pregnant women:

• Use cervical broom or combination of swab and Ayre's spatula 2
• Avoid cytobrushes in pregnancy due to manufacturer concerns about potential amniotic sac perforation, though considerable clinical experience exists without complications 1, 2
• If endocervical brush is used despite pregnancy, employ the same gentle technique with 180-degree rotation 1

Common Pitfalls to Avoid

• Never use cotton swabs for endocervical sampling in non-pregnant patients—they are significantly less sensitive than endocervical brushes and should be discouraged 1
• Do not use the broom device alone if high-quality sampling is critical, as 47% of clinicians with high rates of absent endocervical cells used the broom exclusively 3
• Avoid excessive rotation of the endocervical brush beyond 180 degrees, as this causes bleeding without improving cellular yield 1
• Do not skip endocervical sampling—at least one-third of false-negative cytology results are due to sampling issues where abnormal cells were never collected 1
• Recognize that presence of infectious agents decreases sample quality (OR = 3.09, P < .001), so consider treating active infections before screening when feasible 3

Quality Assurance Measures

• Ensure the sample contains endocervical cells or immature squamous metaplastic cells to verify transformation zone sampling 4, 5
• For conventional smears, immediately fix the specimen with spray fixative or 95% ethanol to prevent cellular desiccation 1
• Liquid-based cytology is preferred as it produces fewer inadequate readings and false-negative results compared to conventional smears 2
• Healthcare providers who receive retraining on Pap test collection obtain more satisfactory results 2