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Tests done at colposcopy

There are two different techniques used to identify abnormal cell changes during the colposcopy examination:

1. Acetic acid colposcopy:

Acetic acid (dilute vinegar) is applied to the cervix using a cotton wool ball or with a spray. Abnormal areas, such as CIN, will tend to turn white (acetowhite). It is important to say that some areas of acetowhite do not indicate CIN at all. One of the challenges facing the colposcopist is to decide which areas of acetowhite truly represent areas of abnormal cells that need to be removed so that over treatment is avoided.

2. Schiller's iodine test:

The colposcopist may do another test using an iodine solution. Normal tissue on the outside of the cervix stains dark brown when iodine is applied. However, cervical abnormalities may not stain with iodine which helps the colposcopist to locate any areas of abnormal cells. This test may be used following acetic acid colposcopy and is often used before treatment.


Most colposcopists use a combination of the acetic acid and Schiller’s iodine tests. If there is an abnormality the colposcopist should be able to estimate whether or not treatment will be needed according to:

  • How white the tissue goes after using acetic acid
  • How quickly the tissue turns white
  • How smooth or irregular the surface is
  • The different patterns of the blood vessels (mosaic and punctation) under the surface of the cervix.

Taking a biopsy

To be sure of the diagnosis, a biopsy is often required – this means taking a sample of tissue from the cervix. Depending on the results of this biopsy the colposcopist will decide whether you need treatment. There are two types of biopsy that could be offered. A diagnostic or punch biopsy, which is a small biopsy that often doesn’t require local analgesia (anaesthetic). Two or three punch biopsies may be taken at the first visit. The second type of biopsy is a loop excision, which is slightly larger and does require local anaesthetic. This type of biopsy is usually a treatment biopsy and under certain circumstances can be performed at the first visit in some clinics.

If the colposcopist can immediately tell that you will need treatment this can be done during the same visit – in this case all of the abnormal area is removed and this constitutes the biopsy. Other more invasive types of treatment require a separate appointment.

Treatment options will be outlined to you in your information leaflet before your clinic appointment and will be discussed with you in the clinic. Sometimes taking the biopsy can be uncomfortable, but the person performing the colposcopy will warn you about this before the biopsy is taken. Your colposcopy shouldn’t be painful and if you have any difficulty you should discuss this with the colposcopist. If necessary the colposcopy can be stopped.

Date last updated: 
22 Jan 2016
Date due for review: 
26 Jan 2019

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