5.1 Coverage is defined as the percentage of women in a population who were eligible for screening at a given point in time and who were screened adequately within a specified period. For the complete target age group (25 to 64 years), coverage is calculated as the number of women in this age group who have had an adequate screening test within the last 5 years as a percentage of the eligible population aged 25-64.
The eligible population is the Primary Care Trust’s responsible population30. Women ineligible for screening, and thus not included in the numerator or denominator of the coverage calculation, are those whose recall has been ceased for clinical reasons (most commonly due to hysterectomy).
5.2 Local level coverage is calculated for Primary Care Organisations (i.e. Primary Care Trusts or Care Trusts). Although PCOs do have a defined geographical boundary, the populations used are not those of women resident within the PCO boundaries. Instead the populations of women for whom each PCO is responsible are used. Responsible populations include women on the list of GPs who comprise the PCO, regardless of which geographical PCO they live in; where women on the call/recall register are not under the care of a GP at the time coverage is calculated, they are allocated to a PCO on a geographical basis.
30 The PCTs responsible population comprises:
- all persons registered with a GP whose practice forms part of the PCT, regardless of where the person is resident, plus - any persons not registered with a GP who are resident within the PCTs statutory geographical boundary
Note that persons resident within the PCTs geographic area, but registered with a GP belonging to another PCT, are the responsibility of that other Primary Care Trust.
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99 5.3 Cytology tests result categories
The terms “potential cancer”, “abnormal”, “negative” and “inadequate” used in the text to describe the result of a cytology test are defined as follows in terms of the categories used on the cytology report form HMR 101/5:
Abnormal: HMR 101/5 cat. 8 (borderline changes), cat. 3 (mild dyskaryosis), cat. 7 (moderate dyskaryosis), cat. 4 (severe dyskaryosis), cat. 5 & 6 (see Potential Cancer below); Women who have an abnormal test categorised as result code 3 or 8 may be recalled early for another test and referred if the abnormality persists. Women who have an abnormal test categorised as result code 4, 5, 6 or 7 will be referred immediately for further investigation, i.e. colposcopy.
Potential cancer: HMR 101/5 cat. 5 (severe dyskaryosis/?invasive carcinoma) or cat. 6 (?glandular neoplasia); women who have such test results should be referred urgently for further investigation.
Negative: HMR 101/5 cat. 2 (negative); women with a negative test result will usually be returned to the screening programme to be called again at the normal interval (3 or 5 years). Shorter recall intervals may be appropriate for women under surveillance or follow-up after treatment’
Inadequate: HMR 101/5 cat. 1 (inadequate); inadequate means it was not possible to obtain a valid result from the sample. Women with inadequate samples will be recalled for a repeat test. Women with multiple consecutive inadequate results may be referred for further investigation.
5.4 Positive Predictive Value (PPV): Positive Predictive Value is a measure of the laboratory’s ability to predict CIN2 or worse from tests with results of moderate dyskaryosis or worse. PPV relating cytology with histology is calculated from outcomes of referral for tests with results of moderate dyskaryosis or worse as follows:
(Numerator / Denominator) x 100
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Numerator: Number of tests with results of moderate dyskaryosis or worse with outcome of referral: cancer, adenocarcinoma in situ, CIN3 or CIN2.
Denominator: Number of tests as per numerator, but also including outcomes of CIN 1, HPV only, No CIN/HPV and 'seen in colposcopy - No Abnormality Detected' (where result was moderate dyskaryosis or worse).
5.5 CIN (cervical intra-epithelial neoplasia) CIN is not cancer but an indicator of the depth of abnormal cells within the surface layer of the cervix, and is divided into 3 grades.
The higher the number/grade the more severe the condition:
• CIN 1 – one third of the thickness of the surface layer of the cervix is affected.
• CIN 2 – two thirds of the thickness of the surface layer of the cervix is affected.
• CIN 3 – full thickness of the surface layer of the cervix is affected (also known as carcinoma in situ)
5.6 HPV Sentinel Site Several areas have been operating an HPV triage protocol programme, whereby women with a cytology result of mild dyskaryosis or borderline changes are initially tested for the presence of HPV and only women who have high risk HPV infection are referred for further investigation. This can speed up referral to colposcopy where required and avoid referral where HPV is not found. If the HPV test is negative, women are returned to the screening programme for routine recall. Further information is available from:
www.cancerscreening.nhs.uk/cervical/hpv-triage-test-of-cure.html
5.7 Percentile A percentile is the value of a variable below which a certain percent of observations fall. For example, the 10th percentile is the value (or score) below which 10 percent of the observations may be found.
5.8 In the tables: .. = Not available
- = Zero
5.9 For definitions of further medical terminology please visit the NHS Cancer Screening Programmes website at www.cancerscreening.nhs.uk
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