S8 Flashcards
Define screening
A preventative measure – the process of identify healthy people who may have an increased chance of a disease or condition
What are the five criteria needed to be satisfied for implementing a screening programme?
The condition, the test, the intervention, the screening programme, implementation
Describe the condition criteria of a screening programme.
Must be an important health problem (frequency/severity) with understood epidemiology, incidence, prevalence and natural history. Carriers of mutation are identified as a result of screening. Has cost-effective primary prevention
Describe the test criteria of a screening programme.
Simple, safe, precise and validated screening test. Agreed policy on further diagnostic investigation of those that test positive and choices available to them. Agreed cut-off level on distribution of test values
Describe the intervention criteria of a screening programme.
There is evidence that intervention at pre-symptomatic phase leads to better outcomes for the screened individual compared with usual care.
Describe the screening programme criteria of a screening programme
There is proven effectiveness in reducing mortality or morbidity through high quality research.
evidence that the complete screening programme is clinically, socially and ethically acceptable to health professionals and the public.
benefits outweigh harms
Describe the implementation criteria of a screening programme
Adequate staff and facilities available
evidence-based information available to potential participants to make informed choice
management and monitoring of programme for quality assurance
Describe difficulties of evaluating the effectiveness of screening programmes
Needs to be based on good quality evidence
Lead time bias- early diagnosis falsely appears to prolong survival. Screened patients live same length of time as unscreened but longer knowing they have the disease
Length time bias- screening programmes better at picking up slow growing, unthreatening cases than aggressive, fast-growing ones. Diseases that are detectable through screening are more likely to have a favourable prognosis, and may indeed never have caused a problem
Selection bias: “healthy volunteer” effect- people that do other things that protect them from disease. Randomised Controlled Trials help with bias
What are the terms used in assessing the effectiveness of a screening test?
Sensitivity (a/a+c) - the proportion of cases which the test correctly detects- disease focussed
Specificity- the proportion of non (d/b+d)- cases which the test correctly detects- disease focussed
Positive Predictive Value (a/a+b)- the proportion of positive tests who are cases- test focussed
Negative Predictive Value (d/C+d)- the proportion of negative tests who are not cases-test focussed
What does a high PPV and a low NPV indicate?
Higher prevalence of disease – the more common a disease, the more likely a “high risk” result will be confirmed as correct
What does a high NPV and low PPV indicate?
Low prevalence of disease- the less common a disease the more likely a “low risk” result will be confirmed as correct
List the advantages and disadvantages of screening for disease, including the dangers of over-diagnosis
Advantages of screening: early detection leading to possibly saving a life
Disadvantages: possible unnecessary treatment i.e curing people that didn’t need curing, lead time bias, length time bias, selection bias
Identify the role of shared decision-making in areas relating to screening
The patient makes the decision to undergo the screen, however the results of the screen then decide what follows, decision made by both patient and doctor.
