Presentation on theme: "Screening in arterial disease: ethical and methodological issues P Lacroix and V Aboyans."— Presentation transcript:
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
Mason JM et al. J Public Health Med 1993;15:154–60 Population screening for abdominal aortic aneurysm Decision tree structure
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).