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 testDuplex 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).