A Brief Analysis of the Influencing Factors of False Negatives in Cervical Liquid-Based Cytology

The latest research data indicate that, from 2023 to 2024, the cervical cancer screening rate among women aged 35–64 in China reached 51.5%, successfully meeting the national target of achieving a 50% screening rate by 2025. As a crucial method for cervical cancer screening, Liquid-Based Cytology (LBC) can effectively detect cervical cancer and its precursor lesions. However, a certain proportion of false negatives persists in clinical practice. The entire diagnostic process of cervical LBC, including sample collection, slide preparation, and diagnosis, contains corresponding steps that contribute to false negative results. This paper attempts to analyze the causes contributing to false negatives in cervical Liquid-Based Cytology.

1. Patient Factors

① Sexual Intercourse within 24 Hours Prior to Sampling

Sexual intercourse within 24 hours prior to sampling leads to an increase in microorganisms, such as bacteria, within the vagina and cervix. This results in a rapid surge in inflammatory cells and increased mucus secretion. Furthermore, cervical friction may cause bleeding. During sample collection, the inflammatory cells and blood cells adhere to the cervical surface, making it difficult to collect cells with diagnostic value, thereby resulting in false negatives.

② Use of Vaginal Suppositories or Douches within 24–48 Hours Before Sampling

Sampling may be contaminated with drug crystals, rendering cell morphology unrecognizable and consequently leading to false negatives.

③ Sampling During Menstrual Period

The presence of a large number of blood cells in the sample collection causes interference during slide examination, leading to false negatives.

2. Sampling Factors

① Inadequate Exposure of the Cervix

The squamocolumnar junction (SCJ) zone is the common site for cervical lesions. Although the number of squamous epithelial cells collected may be sufficient, failure to sample this specific region can still lead to false negatives.

② Insufficient Sampling Force

The sampling head of the cervical collection device requires a certain amount of pressure to fully deploy. Some clinicians may use a gentler technique out of concern for causing bleeding during the procedure, resulting in a failure to collect the lesional cells, thereby leading to false negatives.

③ Lesions Located Deeply

If the lesional area is located too deep from the cervical os (opening), the sampling brush may be unable to reach that site.

3. Slide Preparation Factors

① Impact of Sample Volume

If the volume of sample transfer during slide preparation is not adjusted according to the cell concentration, it may result in an excessively high density of diagnostic cells. These cells, being overlapping, are difficult to observe after staining, thus leading to false negatives.

② Vortexing Prior to Slide Preparation

Failure to adequately vortex/shake the vial before slide preparation may lead to incomplete cell elution from the cervical brush or insufficient dispersal of mucus, which can also result in false negatives.

③ Failure to Fix Promptly After Preparation or Using Air-Drying

Delayed fixation can cause the smear to dry out, leading to cellular degeneration. Additionally, air-drying (or dry fixation) can compromise the fine nuclear structure, making it impossible to evaluate. Both scenarios may lead to false negatives.

Note 1：A. Excessive inflammatory cells; B. Cellular overlapping; C. Excessive blood cells; D. Air-drying

4. Screening Factors

Cytotechnologists may fail to perform an adequate evaluation of the entire slide, or their limited screening experience may prevent a correct diagnosis. Additionally, a heavy workload, resulting in visual fatigue from reviewing too many slides, can lead to missed diagnoses.

In summary, numerous factors contribute to false negatives in cervical Liquid-Based Cytology (LBC). However, with the development of LBC slide preparation automation technology and liquid based cytology technique, the application of Artificial Intelligence (AI) assisted screening, the strengthening of training for screening personnel, and the implementation of robust quality control (QC), the occurrence of false negatives in cervical LBC is expected to steadily decline.

References:

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