Ma'asah, Mohd. Shariman Md. Shah @
(2007)
Comparison of thinprep™ monolayer
cytology versus conventional pap
smear and the correlation with human
papilloma virus detection using hybrid capture® 2 system.
Masters thesis, Universiti Sains Malaysia.
Abstract
Pap smear is a useful screening tool for cancer of the cervix. Screening has resulted in the
tremendous fall in cervical cancer incidence worldwide. However, the conventional pap
smear has many limitations due to significant false negative and false positive rate, and
unsuitability due to thick smears. Liquid-based cytology, such as ThinPrep™ technique is
an alternative to conventional pap smear. This method provides monolayer cells which
make cytological examination easier. HPV is the cause of cervical cancer. Identification of
the virus is helpful in cervical cancer screening. Hybrid Capture® 2 systems is one of the
examples of HPV testing that is useful to detect high-risk HPV in a large number of
samples.
We embarked on pap smear split-sampling study to determine if monolayer cytology would
give better results than conventional cytology. Six hundred eighty eight women who gave
consent were recruited. We collected the exfoliative cervical samples from all the subjects.
Each sample was smeared as for the conventional pap smears as done routinely and then
rinsed into a liquid buffer (PreservCyt) for monolayer cytology and HPV testing. The
cytological examination was performed in blinded fashion. The performance of
conventional and ThinPrep TM monolayer cytology pap smears was compared. Smears were
classified based on The 2001 Bethesda classification. All cases which had epithelial
abnormalities were further tested for HPV by Hybrid Capture® 2 technique.
We found that adequacy of sampling was 94.3% in conventional pap smear and 89.4% in
TbinPrep™ monolayer cytology. The commonest organism identified was Candida spp
(4.1% in conventional smears, 3.9% by ThinPrepTM) and the agreement study is fair (k=0.27). Diagnosis of ASCUS, LSIL, HSIL and squamous cell carcinoma, were low in
both techniques. The glandular cells abnormalities were also low in numbers. The
agreement studies for LSIL showed k=0.40. The agreement studies for ASCUS, HSIL,
squamous cell carcinoma, AGC (NOS) and adenocarcinoma (NOS) were not done as the
number was too few. The HPV testing of cases with abnormal cytology showed low
positivity (38.5%).
The overall performance of ThinPrep™ is no better than conventional pap smears. The
usage of the ThinPrep™ pap smear does not improve in detecting certain infective
organisms nor abnormal epithelial cells. The low positivity of Hybrid Capture® 2 technique
is questionable. Confirmation with other techniques like PCR is essential.
In conclusion, split sampling gives adequate smears for cytological assessment. It can be
carried out in laboratories working to change from one technique to another.
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