Papanicolaou, known as the "father of modern cytology", published the famous paper "Diagnosis of Cervical Cancer by Vaginal Smear" in 1943, and established the Papillolaou grading method, which has been used for more than 60 years. Although there are many problems in this method, such as the limitation of materials and the blurring of the production background, Papanicolaou's contribution is enormous. Pap smear has become synonymous with cervical cytology and is still used in most small and medium-sized hospitals in China. At the end of last century, two American companies developed automatic devices for liquid-based thin-layer cell production technology, which were put into operation in 1997 and 1998 respectively.

In recent years, this method has been further improved at home and abroad to make it simpler. Liquid-based cells have a wide range of materials, uniform cell smear distribution, clear background and distinct staining levels, which is convenient for microscope observation and obviously improves the detection rate of positive cells. If the price is right, it is possible to completely replace Pap smear. Epithelial cells, such as cervical squamous cell carcinoma and cervical adenocarcinoma, can be observed by this method. Besides observing epithelial cells, trichomonads, candida, actinomycetes, herpes simplex virus and chlamydia can also be detected by this method.