L12 - screening

Question 1

Define screening

Answer 1

The practice of investigating apparently healthy individuals with the object of detecting unrecognised disease/precursors so that measures can be taken to prevent disease and improve prognosis.

Question 2

What challenges does screening face?

Answer 2

Low prevalence populations, high specificity of test is needed

Question 3

How can lower/higher cut off points for diagnostic tests influence diagnoses made?

Answer 3

Higher cut off = lower sensitivity, higher specificity

Lower cut off = higher sensitivity, lower specificity

Question 4

What is the appeal of screening?

Answer 4

People prefer not to get ill, and there is a widespread belief that early detection is better

Question 5

What are the current UK systematic screening programmes?

Answer 5

Antenatal: chromosome abnormalities, infectious disease, sickle cell anaemia and thalassaemia, physical abnormalities
Adult cancer: breast (50-70), cervical (25-64), bowel (60-74)
New born: Physical exam, heel prick test, hearing test
Other: AAA 65(+), diabetic retinopathy 12+

Question 6

What additional health checks currently occur in the UK?

Answer 6

NHS health checks, prostate cancer chlamydia

Question 7

What are the results of UK cervical cancer screening?

Answer 7

67% reduction in stage 1a cancer
95% reduction in stage 3+ cancer
Prevention of 70% cervical cancer deaths
Saves 4500 lives a year

Question 8

What are the results of UK HIV screening programme?

Answer 8

Transmission reduced from 2.1% 2000 to 0.46% 2010-11

Question 9

What are the results of HIV screening in pregnant women in South Africa?

Answer 9

70 000 babies -> <6000 babies

1.3 million new HIV infections prevented globally

Question 10

When was breast cancer screening introduced?

Answer 10

1988

Question 11

What is the screening test for BC?

Answer 11

single or double mammography

Question 12

What is the interval for BC screening?

Answer 12

Every 3 years

Question 13

Approx how many women are screened for BC and how many cancers are detected per year?

Answer 13

2.5 mill invited, 1.9 screened, 15000 cancers detected

Question 14

What are the problems of BC screening?

Answer 14

Over diagnosis

Question 15

How is colorectal cancer screening carried out?

Answer 15

Faecal occult blood screening (stool)

Question 16

How often does colorectal cancer screening occur?

Answer 16

2 yearly from age 60-74

Question 17

What are the criteria for screening programmes set out by WHO?

Answer 17

Disease - important health problem, well recognised and detectable pre-clinical stage, natural history understood, long period between first signs and overt disease
Screening test - valid, simple, cheap, safe, acceptable, reliable
Diagnosis and treatment - adequate facilities, effective, acceptable, safe, cost effective, sustainable

Question 18

What is the 5 year survival rate of prostate cancer?

Answer 18

71%

Question 19

What are the types of bias affecting evaluation of screening effectiveness?

Answer 19

Selection bias - people participating in screening often differ from those who don’t
Lead time bias - screening identifies a disease that would often be identified at a later stage, which may present an apparent ‘improvement’ in survival
Length bias - some conditions develop at a slower rate (longer preclinical stage)

Question 20

Define validity of a screening test

Answer 20

Ability to distinguish between subjects with and without the condition

Question 21

Describe the approaches to screening

Answer 21

Mass - Applies to whole population (usually defined by age or gender)
Opportunistic - The population is approached when they make contact for another reason
Targeted - Select sub-groups thought to be at increased risk
Systematic - The population is called for screening using a register