Most women who have a cervical screening test have a normal result. However, out of 100 women who have cervical screening, about 6 will have abnormal cells in their sample. (NHS Cervical Screening leaflet, ‘Helping you decide’, May 2017)

An abnormal result is not unusual. The screening report may describe abnormal changes in the cells of the cervix as dyskaryosis or dysplasia. This means that some cells of the cervix (the neck of the womb) show changes that may need further investigation. Often such changes can be due to inflammation or infection. It is important to remember that it is extremely rare for an abnormality found at screening to be cancer.

The transformation zone is an area of the cervix where abnormal cells most commonly develop; they can be detected by cervical screening and colposcopy. Two different cervical cell types can become abnormal. The inside of the cervix (endocervix) is lined by glandular cells. The outside of the cervix (ectocervix) is lined by squamous cells.

When abnormalities are diagnosed in the squamous cells (after further tests), these abnormalities are known as CIN. CIN stands for cervical intra-epithelial neoplasia,  which means abnormal cells found on the surface of the cervix.

Abnormal cells can also develop in the inner part of the cervix (see ‘What is CGIN?‘) but it is far more common for them to develop in the squamous cells.

A cervical screening test (also known as a smear test) can show that abnormal cells are present, but it can’t always show how deeply the abnormal cells go into the cervix. In order to diagnose and find the grade of the CIN, further tests may be needed on samples (biopsies) of the abnormal areas of the cervix. The biopsies are looked at under a microscope to find the grade of the CIN. This helps the doctor to decide on the most appropriate type of treatment.

CIN is divided into grades, which describe how far the abnormal cells have gone into the surface layer of the cervix. The cell changes can be classed as CIN1, CIN2 or CIN3. This classification is used to indicate how much of the cervix is affected by abnormal cells. The higher the number, the more of the cervix is affected and so treatment is given to remove the cells.

CIN1 often goes back to normal without treatment but a repeat cervical screening test (smear) is needed to check that the cells have gone. Treatment is usually given to remove CIN2 or CIN3 abnormal cells, also called moderate or severe dyskaryosis or dysplasia (see ‘Treatments and their impacts’).

CIN1 – indicates mild changes; affecting only one third of the thickness of the surface layer of the cervix. These changes are not cancer, and in most cases do not lead to cancer in the future.

CIN2 – indicates moderate changes; affecting two thirds of the thickness of the surface layer of the cervix.

CIN3 – indicates more severe changes (not cancer); affecting the full thickness of the surface layer of the cervix.

Even with CIN2 or CIN3 grade changes, the cell changes are unlikely to be cancer.

CIN3 is not cancer of the cervix, but it is important to treat CIN3 as soon as possible. CIN3 may be referred to as severe dyskaryosis or severe dysplasia. Less commonly, it is called carcinoma-situ, though this term is rarely used these days.

CIN1, 2 and 3 rarely cause any symptoms, such as pain, discharge or bleeding. This is why women who do experience any or all of these symptoms should attend for cervical screening or see a doctor.