A cervical screening test, commonly known as a Pap test, can sometimes return an abnormal result. One such finding is Atypical Squamous Cells—cannot exclude High-grade Squamous Intraepithelial Lesion, or ASC-H. This result indicates that the collected cells appear irregular and might suggest a serious underlying condition. While concerning and necessitating further action, ASC-H is not a diagnosis of cervical cancer, but a warning sign identified during screening.
Understanding the ASC-H Diagnosis
The ASC-H category is part of the Bethesda System used by pathologists to report cervical cytology results. “Atypical Squamous Cells” refers to cells lining the outer cervix that look abnormal but do not meet the criteria for a definitive precancerous lesion. These cellular changes are generally caused by infection with high-risk types of human papillomavirus (HPV).
The critical distinction is the addition of “cannot exclude High-grade Squamous Intraepithelial Lesion (HSIL).” This means the pathologist cannot rule out that the changes are a high-grade precancerous lesion, which is a direct precursor to cervical cancer. This uncertainty places ASC-H in a category of significantly higher clinical concern compared to Atypical Squamous Cells of Undetermined Significance (ASC-US). The ASC-H finding prompts immediate investigation to determine the true nature of the cell changes.
Prevalence of the ASC-H Result
The ASC-H finding is uncommon in the general population undergoing routine cervical cancer screening. The frequency varies among laboratories but is typically low. The incidence of an ASC-H interpretation is estimated to fall between 0.2% and 0.56% of all Papanicolaou (Pap) tests performed annually.
This rate means only two to six results per 1,000 Pap tests are classified as ASC-H. This infrequency highlights its importance, as it carries a much higher risk profile than more common abnormalities like ASC-US or Low-grade Squamous Intraepithelial Lesion (LSIL). This result triggers a specific medical response to prevent disease progression.
Statistical Likelihood of High-Grade Disease
The central question following an ASC-H result is the probability that a high-grade lesion or cancer is present. Studies show the risk of finding high-grade cervical intraepithelial neoplasia (CIN 2 or CIN 3), or HSIL, upon further testing is substantial. The prevalence of CIN 2 or worse (CIN 2+) found on follow-up biopsy typically ranges from 13% to 66%, with a pooled average around 34%. This elevated risk signifies a one-in-three chance that a patient has a severe precancerous condition.
The probability of finding invasive cervical cancer is significantly lower, but this risk is still present in the ASC-H population. The rate of invasive cancer detected upon immediate follow-up is generally small, often less than 1% to 2% of all ASC-H cases. The risk is far greater than for less severe abnormalities; for comparison, ASC-US has an associated risk of CIN 2+ at about 12%.
The presence of high-risk human papillomavirus (HPV) infection refines the risk assessment. Nearly all ASC-H cases are associated with high-risk HPV, with positivity rates between 68% and 84%. For patients testing positive for high-risk HPV, the risk of having a CIN 2+ lesion is markedly increased, estimated between 30% and 47%.
Conversely, patients with an ASC-H result who test negative for high-risk HPV have a much lower risk of high-grade disease, with a CIN 2/3 rate documented around 1.6%. Patients testing positive for HPV-16, the type responsible for the majority of cervical cancers, show a notably higher prevalence of CIN 2/3 lesions compared to other high-risk types. Understanding these statistics dictates the immediate need for diagnostic procedures.
Standard Diagnostic Next Steps
Given the substantial risk of underlying high-grade disease, the standard response to an ASC-H result is immediate referral for a diagnostic procedure called colposcopy. Professional guidelines universally recommend this approach rather than repeating the Pap test. Colposcopy allows the physician to examine the cervix under magnification using a specialized instrument to visually identify any abnormal areas.
During the procedure, a weak acid solution is applied to the cervix, which helps highlight abnormal cell growth, often appearing white. If suspicious areas are visualized, a cervical biopsy is performed, removing a tiny tissue sample for definitive analysis. The biopsy confirms whether the abnormal cells are a high-grade precancerous lesion (CIN 2 or CIN 3) or, rarely, an invasive cancer. The final diagnosis and subsequent treatment plan, such as a LEEP (Loop Electrosurgical Excision Procedure), are determined solely by the biopsy results.