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Specimen adequacy

  1. The biological properties of the tumour
  2. Failure of sampling
  3. Failure of screening

Biological properties of the tumour:

Studies have shown that small CIN lesions (< 0.5cm diameter) and lesions that are high in the endocervical canal are more likely to be missed. Regular smear tests at 3 or 5 yearly intervals will minimise the risk of missing CIN lesion when they are in the earliest stages of development.

Failure of sampling:

A neoplastic lesion may be missed if the whole of the transformation zone is not sampled. This can happen if the sampling device selected by the smear taker is not appropriate for the shape or size of the cervix.  A neoplastic lesion may also be missed if abnormal cells present on the sampling device are not transferred to the slide. Great care should be taken by the smear taker to ensure that as much material as possible is transferred from spatula to slide. It is anticipated that the use of Liquid based cytology will resolve this problem.

Failure of screening:

A false negative report may be issued if the primary screener fails to detect abnormal  cells in the smear. This risk can be minimised if appropriate quality control measures are in place in the laboratory (LINK to module on  Quality Control).

Evaluation of specimen adequacy by the screener is considered by many to be the single most important Quality Assurance procedure that can be provided by the laboratory.

Definition of adequacy

Inadequate smears

Slides may be unsatisfactory for evaluation for any of  the following reasons:

An unsatisfactory smear due to heavy inflammatory response which obscures the cells and air drying which distorts the epithelial cells.
An unsatisfactory smear due to scanty cell content and airdrying.
An unsatisfactory smear taken in the second half of the cycle. There is extensive cytolysis due to Doderlein bacilli.
An unsatisfactory smear due to the fact that blood and polymorphs and debris has obscured all epithelial cells.