At least seven women at St George's Hospital, Tooting, who had abnormal smears and were referred for further investigation by colposcopy -visual examination of the cervix using a specially adapted microscope - are understood to have been misdiagnosed.
One woman who was cleared as normal a year ago is believed now to have cervical cancer. Pre-cancerous changes should have been visible at her earlier examination.
Colposcopy examinations are normally performed by doctors and it is understood that it is the work of one that is being investigated. No patients are being recalled while the initial checks are being carried out.
The hospital last night said: "As part of the Trust's standard review procedures, a small number of colposcopy cases are being reviewed with outside experts. The trust cannot discuss the treatment of individual patients nor is it possible to comment further on the review until it is complete."
It added that the colposcopy service was "working in accordance with the latest national guidelines issued by the NHS".
Julietta Patnick, director of the national screening programme, said women with high-grade abnormalities detected by cervical smear or with persistent low-grade abnormalities should be referred for colposcopy.
If the abnormalities were seen they would be treated immediately and, in nine out of 10 cases, a biopsy, or sample of tissue, should be taken.
However, if no abnormality was seen, possibly because the lesion was too far up the cervical canal, and no biopsy was taken, it could be missed.Reuse content