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 testing in the form of HPV triage
and HPV test of cure 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.
The number of clinics estimated is estimated based on referrals from the Cancer
Screening Programme; referrals from outside the Cancer Screening Programme are
not included in the estimate. The estimated number of clinics also does not include
clinics needed for follow-up smears.
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).
1
If the population is unknown, a suggested population of 300,000 may be assumed as an
approximation.
(4) There are two ways to run the model.
i.
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.
ii.
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 which option 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 which 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 which 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.
3.2 Contact details for further information
Please contact a.r.bessey@sheffield.ac.uk for any queries about this model.