Introduction

The concept of population screening—proactive identification of a condition, disease or predisease state in individuals who presume themselves to be healthy but may benefit from early treatment—is a simple one. The translation of this into a screening programme often raises ethical, conceptual and practical challenges. For clinicians used to dealing with patients symptomatically, there are several key differences to understand between treating patients symptomatically compared with the approach to supporting the delivery of a screening programme.

There is a range of definitions of screening, which may be a source of confusion. McKeown defined screening as ‘medical intervention which does not arise from a patient's request for advice for a specific complaint’.1 This may cover (a) research for the validation of a procedure or (b) tests done for public health reasons, for example, to identify the source of infection in a food outbreak or (c) as a direct contribution to the health of the individual. This third meaning is now the most common. The UK National Screening Committee (UK NSC) defines screening as follows: ‘Screening is the process of identifying healthy people who may be at increased risk of the disease or condition. The screening provider then offers information, further tests and treatment to reduce associated risks or complications’.2

Raffle AE and Gray JAM3 emphasises the point that the population screened believe themselves to be well but widens the purpose of screening to include both (i) to reduce the risk of future ill health, for example, when adults are screened for hypertension, the intervention involves risks with drugs and the risk of stroke is reduced or (ii) to give information, even though the risk cannot be changed, for example, when a pregnant woman who would not contemplate termination of pregnancy chooses to be screened for Down's syndrome, in …