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Screening in arterial disease: ethical and methodological issues. P Lacroix and V Aboyans. Screening: definition « Tests done among apparently well people to identify those at an increased risk of a disease or disorder » Implying in case of positive test:
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Screening in arterial disease: ethical and methodological issues P Lacroix and V Aboyans
Screening: definition • « Tests done among apparently well people to identify those at an increased risk of a disease or disorder » • Implying in case of positive test: • Subsequent diagnostic test or procedure • And/or treatment Resulting in health improvement or harms…
Screening: potential harms • Population: Healthy people (without any complains) • For the subject • Psychological costs of screening? • Every adverse outcome : iatrogenic and preventable • Economical issues: cost for the society • Test performances and population selection
Questions that matter to the subject • What is my risk of dying of this disease if: • I choose not to be screened? • I choose to be screened? • What is my chance for having an “abnormal” screening test result? • If my screening test result is abnormal: what follow-up tests will I need? • what is my chance of having the disease? If my screening test result is normal what is my chance of having the disease anyway? Goyder E et al. J Med Screen 2000;7:123-6
Psychological issue after the test? • Normal Test • Abnormal Test implying a specific treatment • Abnormal Test implying a follow-up • Abnormal Test without any change
Population screening for abdominal aortic aneurysm Decision tree structure Mason JM et al. J Public Health Med 1993;15:154–60
Key points in running a screening programme • Prepare a written protocol covering all aspects of screening • Train staff • Issue motivating – not threatening – invitations and reminders • Give information orally and in writing before the test • Inform all the patients of their results • Follow up all patients with positive results • Evaluate both epidemiological and psychological outcomes of the programme Marteau T M BMJ 1990;301:26-8
Criteria for a screening • The disease • Importance of the disease? • Clear definition of the disease? • Prevalence well known? • The policy • Programme cost effective? • Facilities for diagnosis and treatment available? • Course of action after a positive result acceptable? • The test • Safe, valid and reliable? Grimes DA et al. The Lancet 2002;359:881-4
Test effectiveness? Test performances • AAA • Echography: cut off ? … • PAD • pulse palpation? • ABI: Methods? Cut off? Calculation mode?… • Carotid stenosis • Duplex performances? In most of these situations: dichotomous results (normal-abnormal)
Test effectiveness? • Influence of the population • PPV • VPV • Varying with the prevalence of the disease in the population
Setting of the test • Duplex and DVT • Suspicion of DVT : symptomatic patients • High performances included in a strategy • Screening : asymptomatic subjects • Low isolated performances
Misclassification • False negative • False reassurance • False positive • The high sensitivity in order to reduce the risk false negative is often associated with a low specificity and PPV; it results in: • Anxiety • Further investigations with possible adverse events
4 criteria for an optimal screening (1) The condition: important, and the natural history and epidemiology must be understood. The screening test: simple, safe, precise and acceptable to the general population, and defined diagnostic process following a positive test. Treatment: should lead to better outcomes than treatment provided at the point of clinical diagnosis.
4 criteria for an optimal screening (2) • Screening programme: • should be defined, adequate staffing and facilities should be available to cope with expected demand • the programme should provide value for money, as compared with other areas of medical expenditure. • screening programme should be cost-effective • (and if cost-effective, the most cost-effective form of screening should be implemented).