Investigations and screening - what are the differences and does it matter to family physicians?

Antonio A T Chuh 許晏冬

Executive check-up packages are being offered by private laboratories and private medical practitioners, family physicians and specialists alike. Patients commonly undertake a battery of laboratory tests due to a specific health concern such as recent death of a relative from cancer, or due to non-specific health concerns such as fatigue. The dividing line between investigations and screening is indistinct.

When laboratory tests are being arranged, the family physician should ascertain whether an investigation or a screening procedure is being performed, as the aims, criteria, and potential adverse effects of undertaking these two apparently similar activities are genuinely different.

The usual aims to investigate are to confirm or refute a diagnosis. Other disease-oriented aims include to assess the severity of a disease, to ascertain the cause of a disease, to assess the control of a condition, to assess the results of an intervention, and to monitor the adverse effects of treatment. Patient-oriented aims are to reassure, to buy time, to facilitate acceptance of diagnosis, for employment, or for insurance purposes. In some circumstances, other aims are justifiable, including exclusion of diseases for medico-legal purposes and investigations done for clinical research. Whatever the aims are, they should be clear to the family physician and best made known in an understandable manner to the patient.

The criteria to investigate clearly depend on the aim. In order to confirm or refute a diagnosis, Fraser1 proposed three major criteria: (1) that the result of the investigation could not be obtained by a cheaper, less intrusive method, such as by taking a more focused history or using time as a diagnostic tool appropriately, (2) that the risks of the investigation should relate to the value of the information likely to be gained, and (3) that the result will directly assist in the diagnosis or have an effect on subsequent management.

In contrast, screening, a form of secondary prevention, is "the presumptive identification of unrecognised disease or defect by the application of tests, examinations, or other procedures which can be applied rapidly to sort out apparently well persons who probably have a disease from those who probably do not."2 The most widely accepted criteria are Wilson and Jungner's criteria, well known but frequently ignored. In general, investigations are targeted to the individual patient, while screening should be targeted towards the population. The latter may not hold true, however, when the screening is not being performed as a concerted programme with a clearly-defined target group. However, any individual being offered any screening programme should have a well devised plan with rational screening intervals, rather than as ad hoc check-up packages.

Screening is a medical intervention. Like other medical interventions, its benefits should be balanced against its risks. Screening might generate false positive results causing patient anxiety and uncertainty, and false negative results causing false reassurance and delays in treatment seeking. "Normal" results by screening without adequate pre- and post-test counselling might initiate or perpetuate unhealthy lifestyles and habits. For example, a patient might commence a high-fat diet upon learning that his lipid profile is favourable. "Abnormal" results might lead to a chain of unnecessary investigations and treatments, sometimes invasive. Screening programmes with unjustifiably low cost-effectiveness are sources of economic burden to individuals and to the community. It might be difficult to discuss with patients in terms of sensitivities, specificities, predictive values, and odds ratios. However, many patients would comprehend concepts such as number needed to test and cost per life-year saved.

As family physicians, we are in an excellent position to offer rational investigations and screening for our patients. We know our patients well and the continuity of care facilitates the best use of investigations and screening. We are trained not to focus investigations on single body systems, but the patient as a whole person. We are trained not to focus the diagnosis on the physical axis alone, but the psychological and social axes as well. We are ready to discuss with our patients the benefits and potential harms of an investigation or a screening procedure, and assist our patients to make an informed decision. We are trained to deal with uncertainties, and can afford to adopt a "wait-and-see" approach appropriately to avoid unnecessary investigations. Evidence-based investigations and screening are possible. It does matter when and how we should investigate and screen. The spirit of evidence should thrive in our consultation rooms, not only on computer screens or hidden among piles of journal articles.