Bethesda System and Pap Smear Technique
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Direct answer
The Bethesda System is the standard reporting language for cervical cytology, grading each Pap smear from negative for intraepithelial lesion or malignancy through atypical squamous cells to high-grade squamous intraepithelial lesion and squamous cell carcinoma. A Pap smear samples the ectocervix and the endocervical canal together, and the reported category decides whether the woman returns for routine recall, undergoes HPV testing or is referred for colposcopy.
What you must remember
- Reporting system: The Bethesda System places every cytology result into fixed categories, so laboratories report in one shared language.
- Sampling tools: An Ayre spatula collects cells from the ectocervix around the squamocolumnar junction, and an endocervical brush collects cells from the canal, so both sites must be covered.
- NILM: Negative for intraepithelial lesion or malignancy is the normal report, and the woman simply returns for routine screening recall.
- ASC-US: Atypical squamous cells of undetermined significance is the commonest abnormal category, and reflex high-risk HPV testing decides the next step.
- ASC-H: Atypical squamous cells, cannot exclude HSIL, carries a higher risk than ASC-US and goes straight to colposcopy.
- LSIL and HSIL: Low-grade lesions are usually HPV-related and often regress, whereas high-grade lesions are precancerous and need colposcopy with directed biopsy.
- Screening in India: Under national programme guidance (NPCDCS, now part of NP-NCD), visual inspection with acetic acid is the first-line screening test for women aged 30 years and above, with cytology and HPV testing where facilities allow.
Reading a cytology report, category by category
A cytology report uses fixed category names, and each name points to a predictable next step. The table lists the usual action in most national and international protocols, and it is worth memorising because vignettes test these actions directly.
| Category | Meaning | Usual next step |
|---|---|---|
| NILM | Normal cells, no lesion seen | Routine screening recall |
| ASC-US | Atypia of uncertain significance | Reflex HPV test; colposcopy if positive, return to routine screening if negative (older protocols repeat cytology at 12 months) |
| ASC-H | Atypia, HSIL not excluded | Colposcopy with biopsy |
| LSIL | Low-grade lesion, often HPV-related | Colposcopy, or HPV triage in some protocols |
| HSIL | High-grade precancerous lesion | Colposcopy with directed biopsy |
| SCC | Invasive squamous carcinoma | Urgent referral for staging and treatment |
ASC-US is the commonest abnormal category, and HPV testing exists to separate the few women with precancer from the many without it. ASC-H and HSIL skip that step and go straight to colposcopy, because a missed high-grade lesion is the dangerous error.
Where the exam tries to catch you
Vignettes usually hinge on the next step rather than on the category name itself.
- Trap: Repeating cytology for every ASC-US result. Correct: An HPV-positive ASC-US goes to colposcopy, and an HPV-negative ASC-US returns to routine screening (some older protocols repeat cytology).
- Trap: Sampling only the ectocervix with a spatula. Correct: The endocervical brush is also needed, because glandular abnormalities and adenocarcinoma arise in the canal and can be missed by the spatula alone.
- Trap: Reading a cytology result as a histological diagnosis. Correct: Only colposcopic biopsy histology confirms the CIN grade, while cytology screens and triages.
- Trap: Reading HSIL as invasive cancer. Correct: HSIL is precancer, and carcinoma is reported only as squamous cell carcinoma.
Frequently asked questions
Which sampling tool collects the endocervical sample in a Pap smear?
The endocervical brush collects cells from the endocervical canal, while the Ayre spatula samples the ectocervix. Both are needed because the canal can harbour glandular abnormalities and adenocarcinoma that the spatula may miss.
What is the next step after an ASC-US report in a Pap smear?
Reflex high-risk HPV testing is the usual next step after an ASC-US report. A positive HPV result leads to colposcopy, whereas a negative result means return to routine screening, although older protocols repeat cytology at 12 months, so local protocol should be followed.
How does ASC-H differ from ASC-US in management?
ASC-H means atypical squamous cells in which high-grade disease cannot be excluded. Because the risk of underlying HSIL is higher, ASC-H is referred directly for colposcopy rather than being triaged by HPV testing first.
What does an HSIL report mean for the woman?
HSIL means a high-grade squamous intraepithelial lesion, which is precancerous rather than invasive cancer. It needs colposcopy with directed biopsy, and treatment is usually considered when histology confirms CIN2 or CIN3.
Which screening test is first line for women aged 30 and above in the Indian national programme?
Visual inspection with acetic acid is the first-line screening test for women aged 30 years and above under national programme guidance. Cytology and HPV testing supplement it where laboratory facilities allow.