Screening in arterial disease: ethical and methodological issues

1. Screening in arterial disease: ethical and methodological issues P Lacroix and V Aboyans

2. 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…

3. 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

4. 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

5. Psychological issue after the test? • Normal Test • Abnormal Test implying a specific treatment • Abnormal Test implying a follow-up • Abnormal Test without any change

6. Population screening for abdominal aortic aneurysm Decision tree structure Mason JM et al. J Public Health Med 1993;15:154–60

7. 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

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

9. 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)

10. Test effectiveness? • Influence of the population • PPV • VPV • Varying with the prevalence of the disease in the population

11. Setting of the test • Duplex and DVT •  Suspicion of DVT : symptomatic patients • High performances included in a strategy • Screening : asymptomatic subjects • Low isolated performances

12. 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

13. 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.

14. 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).