Screening Flashcards
This is the widespread use of a simple test for a disease in an apparently healthy (asymptomatic) population)
Screening
This is an organised system using a screening test among asymptomatic people in the population to identify early cases of disease in order to improve outcomes.
Screening programmes
Used to test large numbers of apparently healthy people to identify individuals suspected of having early disease who will then go on to have further diagnostic tests to confirm the diagnosis.
Screening test
What is the main difference between a screening test and a diagnostic test?
There is greater emphasis on cost and safety in screening test than in a diagnosis
- screening test: presence of preclinical disease (when people are asymptomatic)
- diagnostic test: measures presence/absence of clinical disease (people become symptomatic)
What type of prevention is screening?
Secondary prevention
The aim of this is to identify people likely to have pre-clinical disease.
Screening test
The aim of this is to establish the presence/absense of a disease
Diagnostic test
When should screening tests be performed?
Before the development of clinical disease
What is the target population of screening tests?
Asymptomatic individuals who are potentially at very high risk for a disease
This aims to improve outcomes and reduce mortality (death due to disease)
Screening
This is also known as opportunistic screening.
Case finding
What are the 4 points to consider when considering when to screen?
- seriousness of disease
- ability to alter course of disease
- lead time
- prevalence of preclinical disease
Why screen just for diseases with potentially severe consequences?
Because screening is resource intensive and it is more efficient when there is a high prevalence of pre-clinical disease.
- there’s no point in screening for the flu
This is the period of time when disease is detected through screening to when when a disease is detected/diagnosed symptomatically.
Lead time
This is the period of time between the biological onset of disease and the appearance of symptoms.
Pre-clinical disease
This is the proportion of people with the disease who test positive.
Sensitivity
This is the proportion of people without the disease who test negative.
Specificity
What are 2 ways to maximise sensitivity and specificity?
- improving screening test
- choice of disease threshold
This measures test performance in a particular population.
Predictive values
These 2 measure the intrinsic properties of a test. Measures what proportion of people with or without the disease the test correctly classifies.
Specificity and Sensitivity
What influences predictive values?
Prevalence in the population of interest
What are 2 things to consider when thinking about the effectiveness of screening programmes?
- resource availability
- evaluating effectiveness (is it actually effective)
What are the 3 benefits of screening programmes?
- early detection and intervention (for true positives) (reduced mortality/morbidity and to require less radical treatment)
- reassurance (for true negatives)
- improved health of population
This is when screening is biased towards detecting slowly developing disease that may have never required treatment.
Length bias
This is a result of when overdiagnosis and/or overtreatment may increase morbidity without reducing mortality. (false positives).
Lead time bias
What are some potential harms of screening? (4)
- missed cases of disease (false negatives)
- cost-effectiveness
- over diagnosis and treatment (specifically for false positives)
- decreased health equities (because not everyone will participate equally in the screening programmes)
