Session 6 Screening
Cards (23)
- Disease Detection - three methods:
- Spontaneous presentation
- Opportunistic case finding
- Screening
- Systematic attempt to distinguish between apparently well persons who are considered likely to have the disease in question, from those considered not likely to - screening
- Advantages of Screening?
- Early detection and treatment
- Prevention and Risk Reduction
- Public health benefits
- health education and awareness
- Cost-effective
- Disadvantages of screening?
- False positives and negatives
- Overdiagnosing and overtreatment
- Ethical considerations
- Resource allocation
- Logistical challenges
- NHSPopulation Screening Programmes :Screening for Adults
- Diabetic eye screening (from age 12 and above annually)
- Cervical cancer
- Breast cancer
- Bowel cancer
- Abdominal Aortic Aneurysm (AAA)
- Breast cancer screening is offered to women aged 50 to 70 -Women aged 70 and over can self-refer.
- Cervical screening is offered to women/people aged 25-64 - Every 3 years between the ages of 25-49 years, and - Every 5 years between the ages of 50-64 years.
- NHS bowel cancer screening is offered to people aged 50 or over - 50 to 74, you'll automatically be invited to do a home testing kit every 2 years (FIT test) - Over 75, you can ask for a kit every 2 years by calling.
- AAA - all men at 65 offered a single ultrasound screening scan.
- Screening in pregnancy?
- Infectious diseases (hepatitis B, HIV and syphilis)
- Fetal Anomaly screening (Down's syndrome T23, Patau's syndrome T13 and Edwards' syndrome T18)
- Sickle cell disease and thalassaemia
- 20-week scan to check the physical development of the baby
- Diabetic eye screening if you are pregnant and have type 1 or type 2 diabetes
- Screening for newborn babies?
- Physical examination, which includes the eyes, heart, hips and testes.
- Hearing test
- Blood spot test to check if the baby has any of 9 rare conditions (e.g Sickle cell disease, Cystic fibrosis, Congenital hypothyroidism, phenylketonuria, medium-chain acyl-CoA dehydrogenase deficiency, maple syrup urine disease, isovaleric acidaemia, glutaric type 1, homocystinuria).
- Criteria for screening programmes: Wilson & Jungner criteria
- Disease/condition
- Test
- Treatment
- Programme
- Implementation criteria
- Test validity represents the extent to which a test measures what it intends to measure.
- Can be thought of as the accuracy of the test.
- Measured by sensitivity and specificity.
- Determined by comparing a new test with the gold standard test.
- Sensitivity: The ability of a test to correctly identify an individual as having a disease. These are individuals who actually have the condition (e.g., a disease) and test positive for it.
- Sensitivity= true positives / (true positives + false negatives)
- Specificity: The ability of a test to correctly classify an individual as ‘disease-free’.
- Specificity= true negatives / (true negatives + false positives).
- a highly specific test can help to rule in a disease when positive.A highly sensitive test can help to rule out a disease when negative.
- Positive predictive value (PPV): The proportion of test-positive individuals who actually have the disease. A measure of how accurate a positive test result is likely to be.
- PPV =truepositives/ (true positives + false positives)
- Negative predictive value (NPV): The proportion test-negative individuals who reallydo not have the disease. A measure of how accurate a negative test result is likely to be.
- NPV =true negatives / (true negatives + false negatives)
- Where earlydiagnosis falsely appears to prolong survival: lead time bias.
- Screening programmes better at picking up slow growing, unthreatening cases than aggressive, fast growing ones : Length time bias
- Studies of screening often skewed by ‘healthy volunteer’ effect : selection bias
- Evaluation difficulties?
- Lead time bias
- Length time bias
- Selection bias
- Morbidity vs mortality
- Population diversity and equal access.