Pap Smear Interpretation: Bethesda Classification, HPV Co-Testing, and the ASCCP Management Guidelines

ASC-US with negative HPV? Routine screening. AGC? Colposcopy, endocervical curettage, and possibly endometrial biopsy. Know the difference.

Cervical cancer screening has evolved dramatically, yet the interpretation of results and management algorithms remain a source of confusion for many providers. The shift from cytology-only screening to HPV co-testing and primary HPV screening has changed when and how we act on results. This post walks through the Bethesda classification system, the current screening strategies, and the 2019 ASCCP risk-based management consensus guidelines.

Current Screening Strategies

Age Group	Preferred Strategy	Acceptable Alternatives	Interval
<21 years	No screening (regardless of sexual activity or HPV vaccination status)	None	N/A
21–24 years	Cytology (Pap) alone	No HPV testing in this age group (too many transient infections)	Every 3 years
25–65 years	Primary HPV testing alone (FDA-approved tests) every 5 years	HPV + cytology co-testing every 5 years, OR cytology alone every 3 years	See strategy
>65 years	Discontinue if adequate prior screening and no history of CIN2+	Adequate = 3 consecutive negative cytology or 2 consecutive negative co-tests in prior 10 years, most recent within 5 years	N/A
Post-hysterectomy (total, with cervix removed)	No screening if no history of CIN2+ and the hysterectomy was for benign indications	Continue screening if history of CIN2+ (screen for 25 years after treatment)	N/A

The Primary HPV Shift

The ACS (2020) and USPSTF (2018) now endorse primary HPV testing as the preferred strategy for ages 25–65. This means HPV testing alone—without concurrent cytology—as the first-line screen. If the HPV test is positive, reflex cytology (triage Pap) is performed on the same specimen. This approach has higher sensitivity for CIN3+ than cytology alone. The key HPV genotypes to know: HPV 16 and HPV 18 are highest risk and warrant direct colposcopy referral even with normal cytology.

The Bethesda Classification System

Result	Full Name	What It Means	Management Summary
NILM	Negative for Intraepithelial Lesion or Malignancy	Normal. May note benign findings (inflammation, atrophy, reactive changes).	Return to routine screening per age-appropriate interval.
ASC-US	Atypical Squamous Cells of Undetermined Significance	Mildly abnormal cells that could be reactive or low-grade. Most common abnormal result.	Reflex HPV testing. If HPV(+): colposcopy. If HPV(−): return in 3 years (co-test) or 5 years (primary HPV).
ASC-H	Atypical Squamous Cells, cannot exclude HSIL	More concerning than ASC-US; higher likelihood of underlying CIN2/3.	Colposcopy regardless of HPV status.
LSIL	Low-grade Squamous Intraepithelial Lesion	Equivalent to CIN1/HPV effect. Most regress spontaneously, especially in young women.	Ages 21–24: repeat cytology in 1 year. Ages ≥25: colposcopy (per ASCCP guidelines, management mirrors ASC-US HPV+).
HSIL	High-grade Squamous Intraepithelial Lesion	Equivalent to CIN2/3. Significant precancer risk.	Expedited treatment (LEEP) or colposcopy depending on age and risk factors. Non-pregnant, ≥25, not concerned about fertility: immediate LEEP is acceptable.
AGC	Atypical Glandular Cells	Abnormal glandular cells. Can originate from endocervix OR endometrium. Higher risk of significant pathology than ASC-US.	Colposcopy + endocervical curettage (ECC) for ALL. Add endometrial biopsy if ≥35 years, abnormal uterine bleeding at any age, or AGC “favor neoplasia.”
AIS	Adenocarcinoma In Situ	Glandular precancer of the endocervix.	Colposcopy + ECC + diagnostic excision. Hysterectomy is the definitive treatment for completed childbearing.
SCC / Adenocarcinoma	Squamous Cell Carcinoma / Adenocarcinoma	Invasive cancer on cytology.	Urgent referral to gynecologic oncology.

AGC Is Never Routine

AGC (Atypical Glandular Cells) is the result that demands the most aggressive workup relative to how benign it sounds. Unlike ASC-US, which is usually nothing, AGC carries a 9–38% risk of significant pathology (CIN2+, AIS, or endometrial pathology). Every AGC result requires colposcopy with endocervical curettage. In women ≥35 or with abnormal uterine bleeding, add endometrial biopsy. AGC “favor neoplasia” carries the highest risk and may require diagnostic excisional procedure even if colposcopy is negative.

The ASC-US Reflex Algorithm

ASC-US is the most common abnormal Pap result and accounts for the majority of follow-up decisions in primary care. The reflex HPV test (run on the same specimen) is the triage tool:

• ASC-US + HPV negative: Return to routine screening (every 3 years with co-testing, or every 5 years with primary HPV). The negative HPV essentially rules out significant disease.
• ASC-US + HPV positive (not 16/18): Repeat co-testing in 1 year. If persistent ASC-US/HPV+ or worse, colposcopy.
• ASC-US + HPV 16 or HPV 18 positive: Proceed directly to colposcopy. HPV 16/18 carry the highest CIN3+ risk.

The 2019 ASCCP Risk-Based Management Guidelines

The Paradigm Shift

The 2019 ASCCP guidelines moved from result-based management (same result = same action) to risk-based management (same result + different history = different action). The key principle: management is determined by the patient's estimated risk of CIN3+ based on current results AND prior screening history. Two patients with LSIL may be managed differently if one has a history of normal screens (lower risk) and the other has prior ASC-US (higher risk). Use the ASCCP management guidelines app or risk tables at asccp.org.

Special Populations

Ages 21–24

HPV is extremely common and usually transient in this age group. Management is more conservative: ASC-US and LSIL are managed with repeat cytology in 1 year, not immediate colposcopy. HSIL still warrants colposcopy. No HPV co-testing (high false positive rate from transient infections).

Pregnancy

Colposcopy can be performed during pregnancy (no endocervical curettage). Treatment (LEEP, excision) is deferred until postpartum unless invasive cancer is suspected. Cervical biopsy is acceptable during pregnancy if indicated by colposcopic findings.

Immunocompromised (HIV+)

Start screening at age 21 (within 1 year of sexual debut for HIV+). Screen annually with cytology (21–29) or co-testing (30+). After 3 consecutive normal results, can extend to every 3 years. Never stop screening (no age cutoff). HPV persistence and progression are more common.

Post-HPV Vaccination

Vaccinated individuals follow the same screening guidelines as unvaccinated. The vaccine doesn't cover all high-risk HPV types, and patients may have been exposed before vaccination. Screening intervals and management don't change.

The Pitfalls

• Don't Pap women under 21: No exceptions. Even with sexual activity, HPV exposure, or abnormal symptoms. If symptomatic, evaluate the symptoms—don't screen for cervical cancer.
• Don't HPV-test women 21–24: Transient HPV is ubiquitous in this age group. A positive HPV in a 22-year-old causes anxiety and overtesting with no benefit.
• AGC is not ASC-US: The workup is fundamentally different. AGC always needs colposcopy + ECC. Don't just repeat the Pap.
• Post-hysterectomy screening errors: If the cervix was removed for benign indications and there's no CIN2+ history, screening is over. If the cervix was NOT removed (supracervical hysterectomy), screening continues.
• Don't over-screen: Co-testing every year is not indicated for normal-risk patients. It leads to false positives and unnecessary colposcopies. Stick to the recommended intervals.
• Inadequate specimen: An “unsatisfactory” Pap needs to be repeated in 2–4 months, not in a year. Don't let it fall through the cracks.

Bottom Line

Cervical cancer screening saves lives when done correctly—at the right intervals, with the right tests, and with appropriate follow-up. Primary HPV testing is the preferred strategy for 25–65. ASC-US with negative HPV is reassuring. AGC is never reassuring. HPV 16/18 positivity warrants colposcopy regardless of cytology. And the 2019 ASCCP guidelines mean that a patient's screening history now drives management, not just the current result. Use the ASCCP risk tables and manage accordingly.

Stay sharp out there.