Screening Flashcards
What is an indication for screening
When early diagnosis of a disease allows early intervention to improve prognosis
What does a screening test do
Identifies those most likely to have the condition and those least likely to have it
What can low risk individuals be split into
True negatives and false negatives
What can high risk individuals be split into
True positives and false positives
What is represented by letters a, b, c, d
a - true positive
b - false positive
c - False negative
d - True negative
What is sensitivity and how do you calculate it
ability to pick up true positives
a/a+c
What is specificity and how do you calculate it
Ability to exclude true negatives
d/b+d
What is predictive value and how do you calculate it
Proportion of test results that are correct
a/a+b OR d/c+d
What are the benefits of screening
people prefer not to get ill
Widespread belief that early detection is better
Do no harm
What are the challenges of screening
generally low screening low prevalence populations
high specificity required
Leads to lower sensitivity
How is hypertension screened for
Blood pressure compared to those taken in a doctor’s surgery
Gold standard = measurements over time
Why is choosing diagnostic cut off important
Moving in either direction either causes too many false positives or false negatives
What programmes are currently offered in the UK
Antenatal screening
Newborn
Adult cancer
Other
What is screened for in antenatal screening
Fetal anomalies
Infections e.g. syphillis, HIB, Hep B
Sickle cell and thalassaemia
Physical abnormalities
What is the screening programme for newborns
Physical exam for eyes, heart, hips, testes
Hearing
Blood spots
What cancers are screened for
Breast (F 50-70)
Cervical (F 25-64)
Bowel (60-74)
What other conditions are screened for
Abdominal aortic aneurysm (M 65)
Diabetic retinopathy
What are some additional screening programmes
NHS vascular checks
Prostate cancer
Chlamydia
What is the WHO screening criteria for the disease
Important health problem well
Well recognised pre-clinical stage
Natural history understood
Long latent period
What is the WHO screening criteria for the test
Valid (sensitive and specific)
Simple and cheap
Safe and acceptable
Reliable
What is the WHO screening criteria for the diagnosis and treatment
Facilities are adequate
Effective, acceptable and safe treatment available
Cost effective and sustainable
How often are cervical cancer screens
Every 3 years from 34 and every 5 years >50
How effective is cervical cancer screens
67% reduction in stage 1A and 70% deaths are prevented
