Screening programmes Flashcards
Three cancer screening programmes delivered by the NHS
Bowel cancer
Breast cancer
Cervical cancer
Conditions that make it possible for cancers to be screened
Common cancer
In an asymptomatic but identifiable population
Identifiable premalignant conditions
That can be treated to reduce mortality and morbidity
Who is screening intended for?
People without symptoms
Which organisations coordinate these screening programmes?
National Office of the NHS Cancer Screening Programmes
Who receives bowel cancer screening kits?
Incidences increase after 50 years of age
If registered with GP, will automatically receive kits if aged 60-74
What does the bowel cancer screening kit contain?
A prepaid return envelope
An orange and white cardboard test kit
6 cardboard sticks to collect stool samples
Instructions and information leaflet
How does the faecal occult test work?
Collect stool samples on 3 different days
Samples collected with cardboard sticks and transferred to collection kit
Kit is then posted back in a prepaid envelope
Should be received at the pathology laboratory at a screening centre within 14 days
Within how many days should the faecal occult blood test be received at the pathology laboratory at a screening centre?
Within 14 days
What does the FOBT test for?
Detect hidden blood in the stool
Could be indication of pre-malignant condition or cancer
How are the FOBT analysed?
By a manual qualitative process
What type of FOBT does the NHS use?
Guaiac-based FOBT
What does the kit of the guaiac-based FOBT consist of?
2 paper squares in 3 flaps impregnated with a colourless substance called guaiaconic acid
What happens chemically in the guaiac-based FOBT?
Developing solution containing hydrogen peroxide is added
If there is occult blood in the sample, a guaiac-peroxidase reaction occurs
Colour change from colourless -> blue-green colour within 30 to 60 seconds
What causes the colour change in the guaiac-based FOBT?
Colour change happens because the heme-portion of haemoglobin in red blood cells has peroxidase activity
Peroxidase activity catalyses the oxidation of the colourless gluconic acid by hydrogen peroxide
Why is the peroxidase activity of Hb termed pseudoperoxidase?
Haemoglobin is not a true peroxidase enzyme
What causes the colour change in FOBT?
Hydrogen peroxide produces a blue quinone compound
How should a patient prepare for the FOBT?
Avoid certain medications
Follow dietary restrictions for several days before collecting the stool sample
What dietary restrictions must patients follow before undergoing FOBT?
Avoid food with high peroxidase activity
Red meat Horseradish Broccoli Turnips Vitamin C supplements - high ascorbic acid activity
Could give false positives
What is the advantage of the Faecal Immunochemical Test?
Uses antibodies to globin to identify the presence of blood
The patients must not go under any dietary restrictions
Charity Beating Bowel Cancer has urged Public Health England that this is better option
What is a normal result in FOBT?
None of the 6 windows show colour change
What is an abnormal result in FOBT?
5-6 positive windows
Requires further investigation
Colonoscopy recommended
What is an unclear result in FOBT?
1-4 positive windows
Second kit is sent out
If the second kit is normal, a third kit is sent out
If the second or third kit show 1+ positive spots = weak positive
Colonoscopy recommended
If both subsequent kits are normal then the result is normal
What is sensitivity?
Proportion of individuals with the disease who are correctly identified by the test as positive
What is the sensitivity of the FOBT?
55-92%
Since presence of blood in the stool does not necessarily mean colon cancer
What is specificity?
Proportion of individuals without the disease who are correctly identified as negative
What are the next steps for when FOBT detects blood in the stool?
Further investigation is needed, this usually consists of colonoscopy
People with abnormal results are offered an appointment or phone call with a specialist nurse
What does the specialist nurse explain before the patient undergoes a colonoscopy?
The possible implication of the abnormal screening test result
What a colonoscopy involves
Assess the patient’s fitness for the procedure
Answer any question
What is the specificity of the FOBT?
95%
