University of Sheffield Royal Free Hampstead NHS Trust

Colposcopy capacity model for use by any colposcopy clinic in England

1. Background

The School of Health and Related Research (ScHARR) and the Royal Free Hospital were commissioned by the NHS Cancer Screening Programme to produce a model to evaluate the effect of the recent changes to colposcopy referral strategies upon clinic workload (NHSCSP publication 20 (April 2004). This was with specific reference to the proposal that women should be referred to colposcopy after a single mildly abnormal smear, rather than after two, which had been the traditional policy. The model produced as a result of this work suggested that referral after one mild result instead of two would be expected to increase the workload of a typical colposcopy clinic by between 21% and 35% over three years, and that the increase in workload is likely to be the greatest in the first year following the change in strategy (see http://www.cancerscreening.nhs.uk/cervical/publications).

The model was modified in order for individual colposcopy centres to estimate the number of clinic sessions (a full morning or afternoon of appointments) required to accommodate changes in referral strategies.

1.1 The current model

The model has now been updated to include HPV triage testing as HPV testing has now become part of the screening pathway. Colposcopy centres can now estimate the number of clinic session this change in guidelines will have on their service. This user manual has been produced in order to facilitate the use of the ScHARR/Royal Free Colposcopy Model.


2. Using the model

Macros need to be enabled for the model to run. A box displaying ‘Security Warning: Macros have been disabled’ should appear under the tool bar when the excel file is opened. Click on the ‘options’ button next to it, and a box in the middle of the sheet should appear, click on ‘enable this content’ and then ‘ok’ in the box. Macros should have then been enabled for this excel workbook.

2.1 Model requirements

The model has been produced in Excel and requires the user to:

(1) Choose from a number of current and future policy options.

(2) Enter information about the local patient population and clinic organisation including:

(a) Total population covered by the clinic (this includes total number of men and women in the catchment area)[1];

(b) Screening coverage (% of eligible women having screening smear in the appropriate screening interval);

(c) Total clinic length in minutes, and the length in minutes of different types of appointment;

(d) Attendance, DNA and cancellation rates.

The model will then calculate the number of clinic sessions required per six month period to accommodate the change in referral policies.

2.2 Calculating the number of clinic sessions required

To calculate the number of clinic sessions required for your colposcopy department:

(1)  Click on the ‘choices’ sheet.

(2)  Use the pull down tabs under ‘current policy’ and ‘future policy’ to describe the way in which your clinic currently runs and the way it might be run to accommodate the change in policy.

(3)  Fill in all other details in the blue boxes on this worksheet, where this data is not available we would recommend the use of the default data available (see section 2.3 for more detail).

(4)  There are two ways to run the model.

  1. Click on ‘run these strategies’ at the top of the page. This should produce a table of results (explanation of results’ table over page). This runs the model a single time.
  2. Click on ‘probabilistic analysis’, this runs the model 1000 times and each times samples certain parameters from their distribution. This accounts for some uncertainty surrounding the parameter values and will give more accurate results. It will also give an upper and lower range of the number of clinics needing to be run. This takes around 10-15 minutes to run depending on your computers processing speed. During his time you will not be able to use Excel. To exit while it is running press the Esc key.

(5)  Click on ‘see graph’ to see the results in graph form.

2.3 Definitions and notes regarding model inputs

Management policy

Please choose the description in the pull down menus which most closely match your current and future policies.

Please note that when HPV triage screening type is selected a woman is HPV tested after a single mild or borderline cytology result regardless of what is selected in the mild dyskaryotic smear referral policy and the borderline smear referral policy categories.

Please also note that if the CIN1 management policy is set to ‘Discharge’, all women with CIN1 will be discharged regardless of what option is selected for the CIN1 time-to-treat policy. And if the ‘treat immediately’ option is selected, all women with CIN1 will be treated immediately, regardless of what option is selected for the CIN1 time-to-treat policy.

When HPV triage is selected women who have been referred to colposcopy through HPV triage are discharged to normal screening following a negative colposcopy as recommended in the guidelines.

When the ‘discharge’ option is selected for the ‘post-negative colposcopy policy’ women are discharged from the colposcopy clinic but will undergo further surveillance smears.

Treatment policy

Please fill in according to your current and future policies. For both high and low grade patients please fill in the first two rows (Percentage of patients treated in see and treat and Percentage of patients treated at a later appointment) so that it equals 100%.

For the final two rows of this section (Percentage of treated patients treated excisionally and Percentage of treated patients treated destructively) please fill in so that it equals 100%.

Post-treatment policies

Please fill in according to your current and future policies and please make sure the percentages entered add up to 100% in the 3 rows allocated for each category of CIN.

Population and coverage data

Please fill in according to the population the clinic covers.

Clinic time data

There are three different types of appointment in the model:

1)  Colposcopy only (a diagnostic appointment)

2)  Colposcopy and treatment (a ‘see and treat’ appointment)

3)  Treatment only (for patients who have already had a colposcopy but have had a diagnostic appointment previously rather than a ‘see and treat’ appointment)

Please fill in the length of each of these different appointments in minutes and the total length of the clinic in minutes.

The appointment times for these sessions are assumed to be the same whether the appointment is an initial session or follow up session. If these times are different please enter a weighted average of the two.

Patient attendance data

Please fill in according to your available data.

The proportion of patients attending, cancelling, and the DNA rate should equal 100%.

3. Explanation of model results

3.1 Overview

There are two tables in the ‘results’ worksheet. If you have run a deterministic analysis using the ‘run these strategies’ button then use the first table labelled deterministic results. If you have run a probabilistic analysis use the second table labelled probabilistic results.

These tables provide the number of clinic sessions required for each 6 month period; starting six months prior to the policy changes until 36 months following the changes. The first four rows of the table are the total number of clinics, and the number diagnostic, ‘see and treat’, and treatment clinic sessions that would have been required had there been no policy changes. This allows a comparison to be made with the last four rows; which describe the number of these clinic sessions required after the policy changes. The number of diagnostic, ‘see and treat’, and treatment clinic sessions are the number of clinics needed to be run if each clinic was made up of exclusively one type of appointment. They give an indication of how the policy change has affected the different type of appointments and what type of appointment is driving the increase or decrease in the total number of clinics.

In the probabilistic results table the mean is the average of the 1000 results that have been generated. The percentiles give a likely range that the number of clinics will fall into. The lower percentile indicates that only 2.5% of the results fall below this value, giving a lower value for the number of clinics needing to be run. The higher percentile indicates that 97.5% of the results fall below this value, giving a higher value for the number of clinics needing to be run.

The graphs are very useful in describing the difference in capacity required between the current and future referral strategies. Again, if you have run a deterministic analysis use the first graph labelled deterministic results. If you have run a probabilistic analysis use the second graph labelled probabilistic results.

4. Future updates

4.1 HPV ‘Test of cure’

The model will be updated to include HPV test of cure and should be available in the near future.

4.2 Contact details for further information

Please contact for any queries about this model.

[1] If the population is unknown, a suggested population of 300,000 may be assumed as an approximation.