Block 5 Flashcards
What antenatal screening programmes are run in the UK?
Chromosomal abnormalities (Down's, Edwards' + Patau's) Infectious disease in pregnancy
What infectious diseases are tested for antenatally?
Hep B
HIV
Syphillis
How (and when) are chromosomal abnormality screenings carried out in the UK?
Combined screening test (ultrasound + bloods between 10-14 weeks)
Nuchal translucency (measure of fluid behind baby’s neck on ultrasound)
Chorionic Villus sampling (sample of placenta taken weeks 11-14)
Amniocentesis (amniotic fluid sample taken around 15 weeks)
What is the miscarriage risk for amniocentesis?
1 in 100
What postnatal screening programmes are run in the UK?
Newborn blood spot (approx. day 5 by midwife)
Newborn hearing screening (should be carried out in hospital but can be up to 3 months)
What diseases are screened for in the newborn blood spot?
Sickle Cell Disease, Cystic Fibrosis, Congenital Hypothyroidism, Inherited Metabolic Disorders (e.g. Maple Syrup Urine Disease, PKU)
What is the Wilson + Jungner criteria for implementation of screening programmes?
- Disease must be an important health issue
- Treatment must be available
- Facilities for diagnosis and treatment must be available
- Test must be acceptable to the public
- Disease must have latent period
- Cost-benefit analysis
- Understanding of natural history of disease
- Agreed policy on who to treat
- Diagnostic test must be available
- Continuous process
What is sensitivity of a screening programme and how is it calculated?
Proportion of people that the test correctly detects as having disease
Sensitivity = true positive/ (true positive + false negative)
What is specificity of a screening programme and how is it calculated?
Proportion of people who don’t have the disease that the test correctly detects as not having the disease
Specificity = true negative/ (true negative + false positive)
What is the positive predictive value and how is it calculated?
The probability that a person has the disease given that they had a positive test result
PPV = true positive/ (true positive + false positive)
What is the negative predictive value and how is it calculated?
The probability that a person does not have the disease given that they had a negative test result
NPV = true negative/ (true negative + false negative)
What is the healthy screenee bias?
Those that attend screening test are likely to be healthier as they are more likely to engage in positive health behaviours than those who do not attend the screening (those who don’t attend screening more likely to smoke, drink, have lower income etc.)
What is the length time bias?
Diseases that are slower progressing are more likely to be picked up in a screening programme therefore screened diseases are more likely to have a better prognosis even if it results in no difference in treatment
What is the lead time bias?
Screening programmes can detect illness earlier when it is more responsive to treatment and therefore improve survival rates however useless screening can appear to increase survival time by simply detecting disease earlier but not actually resulting in longer life (essentially just aware of disease for longer)
What is overdiagnosis?
Correct diagnosis of a disease however diagnosis is irrelevant as the disease may never cause symptoms in patient’s life time (e.g. prostate cancer in some men)
