Table of Contents
LIQUID-BASED CYTOLOGY: CERVICAL CANCER SCREENING TEST
INTRODUCTION
Liquid-Based Cytology (LBC) is an advanced method of preparing cervical cell samples for cytological examination, particularly for Pap smears. It enables cells to be suspended in a monolayer, therefore providing a better morphological assessment,
This technique has largely replaced the conventional Pap smears in many labs because it offers better sample quality, easier interpretation, and the ability to perform additional tests, such as HPV testing.
Liquid-based cytology differs from conventional Pap smears in that the cells collected, are suspended directly in a liquid preservative rather than being smeared onto a glass slide.
This way, the cells are better preserved; non-diagnostic materials such as blood and mucus are also removed. These materials would have otherwise been smeared on the slide adding to the bulk of the cell clusters to be examined.
Two common systems used in LBC are:
– ThinPrep
– SurePath
Both systems have similar techniques but vary in how samples are processed and transferred to the slides.
LIQUID-BASED CYTOLOGY PROCEDURE
The healthcare professional uses a speculum for visualization and then collects cells from the cervix with a spatula or brush. Instead of smearing the cells directly onto a slide (as in conventional Pap), the collection tool is rinsed into a vial of liquid preservative.
(The preservative Solution helps maintain cellular morphology and viability, by preventing cell degradation.)
- Processing the Sample
At this stage, the liquid sample is processed to concentrate the cells and remove debris like blood, mucus, and inflammatory cells. This is done through centrifugation or filtration.
Let us explore the individual methods.
Laboratory Procedure for ThinPrep and SurePath
ThinPrep Procedure
- Sample Vial Preparation: The vial, containing the patient’s sample is placed in a ThinPrep processing machine.
- Filtration: The machine filters the sample, capturing cells on a membrane. The filter ensures that only diagnostic cells are collected and the debris is removed.
- Cell Transfer: The filtered cells are transferred onto a glass slide in a uniform, thin layer.
SurePath Procedure
- Sample Vial Preparation: The sample vial is loaded into a SurePath machine, which centrifuges the sample to concentrate the cells. This process separates blood and debris, leaving at the bottom, the diagnostic cell.
- Cell Collection: After centrifugation, the supernatant is carefully removed and the cells are resuspended and transferred onto a slide creating a thin monolayer.
- Slide Staining & Screening: The prepared slides are stained using the traditional Papanicolaou (Pap) staining method. The process ensures that the cells are spread in a monolayer, reducing overlapping and clumping, which is a common issue in conventional smears. The slides are then screened manually by cytotechnologists or cytopathologists. This is discussed extensively in the Pap smear review article.
ADVANTAGES OF LIQUID-BASED CYTOLOGY
- Improved Sample Quality:
LBC reduces obscuring elements (like blood and mucus) in samples, resulting in clearer slides which make it easier to read and interpret.
- Monolayer Cell Distribution:
Cells are evenly spread in a single layer, minimizing cell overlap, and allowing better visualization of individual features.
- Higher Sensitivity:
LBC detects abnormal cells more effectively than conventional Pap smears. The clearer slides and improved cellular preservation contribute to this sensitivity.
- Multiple Tests from One Sample:
LBC allows additional molecular tests (e.g., HPV testing) on the same sample. There is no need for a second collection—comprehensive diagnostics in one go.
- Reduced Inadequate Samples:
Fewer samples are reported as “unsatisfactory for evaluation.” Results in fewer repeat tests and faster diagnosis.
CHALLENGES AND LIMITATIONS
- LBC is more expensive than conventional Pap smears due to the cost of equipment and supplies.
- The LBC may take a little more time, than the conventional pap smear due to the additional steps involved; such as centrifugation or filtration.
- Special training is required for proficiency in this method.
- Like all automated systems, LBC machines require regular maintenance to function optimally.
Liquid-based cytology represents a milestone in cervical cancer screening. By improving sample quality, reducing the presence of obscuring materials, and allowing for additional molecular testing, LBC has enhanced the accuracy and efficiency of Pap smears.
References
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9345114/?utm_source
- https://cytojournal.com/liquid-based-cytology-technical-aspects/?utm_source=perplexity
