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Liquid Βased Pap Smear


Liquid-based cytology (LBC) is a different way to do the Pap test. Developed in the 1990s, this method presents the following differences compared to the conventional Pap test, resulting in increased sensitivity:

Sample collection and transfer
In the conventional Pap test, the cells are collected and smeared directly onto glass slides, and they need to be fixed immediately; usually, using a spray fixative. The problems with this approach are that not all cells are transferred onto the slides, the cells are not in a single layer, the slides can be broken during transportation and the cells can be damaged until they arrive at the lab. In LBC, the cells are placed into a vial with a preservative, which preserves them for weeks and protects them from damage during transport to the lab. The slide, with the cells in a single layer, is prepared in the lab and not by the doctor or nurse.

Sample adequacy
In the conventional Pap test, samples with a lot of blood, mucus and inflammatory cells are typically considered 'unsatisfactory for interpretation' and, as a result, patients are often recalled.

Slide clarity
Conventional slides do not feature a clear background or organize cells in a single layer. These limitations make finding abnormalities harder, which can impact the accuracy of results.

With the conventional Pap test, additional molecular and biomarker tests cannot be run. The ability to run such tests is important in today's environment with evolving guidelines.

Benefits also include:

  • Patient comfort — only a single specimen needs to be collected.
  • Convenience — less handling of vials in your practice.
  • Efficiency — lab results more likely to be reported together.
  • Ensures chain of custody — less chance for losing or mixing up samples.
  • The sample is collected, normally by a small brush, in the same way as for a conventional smear test, but rather than the smear being transferred directly to a microscope slide, the sample is deposited into a small bottle of preservative liquid. At the laboratory the liquid is treated to remove other elements such as mucus before a layer of cells is placed on a slide. The technique allows more accurate results. 
Health Tips 

What is a Pap test?


Who should have a Pap test and how often?


No Pap test screening for women aged 20 and younger
Start Pap test screening at age 21
Screen every 2-3 years for women aged 21-29

What is the difference between screening and diagnostic Pap tests?


How is a Pap test done?




Sexual intercourse
Use of a douche
Use of a tampon
Use of medicine or spermicidal foams
Use of jellies or vaginal cream

How is a Pap test evaluated?


How is a Pap test reported?




What does this Pap test diagnosis mean?






Advantages of the Liquid Based Cytology

Advantage 1: - Due to the extra sensitivity, there is less likelihood of being recalled for testing.
♦ Advantage 2: - The liquid based test improves the chance of disease being detected and early treatment of pre-cancerous changes on the cervix.
♦ Advantage 3: - The new test reduces the rate of false negative reports when disease is in fact present.

liquid-Based Cytology

An important landmark in the history of the Pap test occurred in 1996 when the U.S. Food and Drug Administration (FDA) approved the ThinPrep™ (Hologic, Marlborough, Mass.) as an alternative to the conven- tional cervicovaginal smear. This was followed 3 years later by approval of the AutoCyte Prep™ (now known as SurePath™; BD TriPath, Burlington, NC). The newest LBC is the MonoPrep™ (MonoGen, Inc., Lincolnshire, Ill.), which was approved in 2006. LBCs were an important step in the development of automated Pap screening devices—an improved preparation was needed to min- imize cell overlap so that automated screeners would perform better in identifying abnormal cells. But LBC performed so well in clinical trials against conventional smears that it found a market independent of auto- mated screening. Although there are exceptions, the great majority of peer-reviewed studies, some of them detailed in this chapter, show an increased detection of low-grade squamous intraepithelial lesions (LSILs) or HSILs with LBC. The debate over increased disease detection with LBC continues, however, and the stud- ies comparing LBC to smears have come under criticism for allegedly sacrificing methodologic purity in their design.26 Nevertheless, LBC offers several clear advan- tages over conventional smears: the opportunity to pre- pare duplicate slides and even cell block preparations from the residual sample; the option of “out-of-vial” aliquoting for HPV, chlamydia, and gonorrhea testing; an improved substrate for automated screening devices; and a thinner cell preparation that most pathologists and cytotechnologists find less tiring to review than smears.

ThinPrep Pap Test

The practitioner obtains the ThinPrep Pap sample with either a broom-type device or a plastic spatula/endocer- vical brush combination.
The sampling device is swirled or rinsed in a methanol-based preservative solution (PreservCyt) for transport to the cytology laboratory and then discarded. Red blood cells are lysed by the trans- port medium.
The vials are placed one at a time on the ThinPrep 2000 instrument. The entire procedure (Fig. 1.1A) takes about 70 seconds per slide and results in a thin deposit of cells in a circle 20 mm in diameter (con- trast with cytospin: diameter = 6 mm).
A batch-process- ing version (the ThinPrep 3000) is also available. It uses the same consumables (filters and solutions) but allows automated processing of 80 samples at one time. In most cases, only a fraction of the sample is used to prepare the slide used for diagnosis. If needed, the residual sample is available for additional ThinPrep slide preparation, cell block preparation, or molecular diagnostic testing (e.g., high risk HPV, chlamydia, gonorrhea).
A multicenter, split-sample study found that the ThinPrep detected 18% more cases of LSILs and more serious lesions as compared to conventional smears, with no significant difference in the detection of organ- isms. A number of studies have shown significant increases in HSIL detection after the implementation of the ThinPrep.
The ThinPrep is equivalent to the conventional smear in the detection of endocervical AIS.36 Data also show comparable results between ThinPrep slides and conventional smears for the detection of endometrial pathology.
The ThinPrep collection vial has been approved by the FDA for direct testing for HPV, which is particularly useful for managing women whose Pap tests show atypi- cal squamous cells (ASC)

SurePath Pap Test

TriPath Imaging (acquired by Becton Dickinson in 2006) developed the SurePath Pap test (formerly AutoCyte Prep and CytoRich) for samples collected in an ethanol-based transport medium.
In contrast to the ThinPrep and MonoPrep methods, the practitioner snips off the tip of the collection device and includes it in the sample vial.
The equipment to pre- pare slides includes a Hettich centrifuge and a PrepStain robotic sample processer with computer and monitor. The PrepMate™ is an optional accessory that automates mixing the sample and dispensing it onto the density reagent. Red blood cells and some leukocytes are elimi- nated by density centrifugation. In addition to preparing an evenly distributed deposit of cells in a circle 13 mm in diameter, the method incorporates a final staining step that discretely stains each individual slide.
A multicenter, split-sample clinical trial showed a 7.2% increase in the detection of LSILs and more serious lesions and a significant decrease in the percentage of unsatisfactory specimens

MonoPrep Pap Test

The practitioner obtains the MonoPrep sample with standard collection devices that are swirled or rinsed in a preservative-filled collection vial, after which the sampling device is discarded. As with the ThinPrep, red blood cells are lysed by the transport medium. The vials are delivered to the laboratory where slides are prepared using the MonoPrep Processor, a fully automated, batch- processing instrument capable of processing 40 samples per hour, with a throughput capacity of 324 samples per 8-hour run. In a split-sample clinical trial similar in design to the ThinPrep and SurePath trials, slides prepared by the MonoPrep method showed a 26% increase in the detection of LSILs and more serious lesions, with no significant difference in relative specificity. MonoPrep provided a signifi- cant reduction in unsatisfactory slides, and there was no difference in the presentation of endocervical or trans- formation zone component or the detection of benign conditions.