Near-patient tests in primary care: setting the standards for evaluation

Near-patient tests (NPT) are an area of rapid technological advance that may enhance the quality of care given by primary care physicians by enabling more accurate diagnosis or more reliable monitoring of therapy. Unfortunately, many new diagnostic technologies prove disappointing in practice, either because of limitations of the technology or because of a failure to address setting-specific issues that were not apparent during their evaluation. A recent systematic review of NPT in primary care has highlighted the methodological weaknesses of most published evaluations. There is a need for a formal statement of the criteria by which to judge the quality of evaluations in this field. In a similar fashion to Wilson and Junger's criteria for screening, seven questions need to be addressed. These cover the performance, reliability and acceptability of the test, its impact on decision-making, comparison with existing practice, cost-effectiveness of the test and integration with the practitioner's knowledge base. Evaluations of NPTs should therefore address the following methodological issues: demonstration of the need for the NPT, definition of the appropriate reference standard, calculation of sample size based on modelling of the decision problem and defining acceptable limits to the likelihood ratio, avoidance of verification bias, selection bias and treatment paradox, testing for the presence of spectrum bias, reporting the sensitivity of the results to changes in setting or prevalence or disease and calculating cost-effectiveness.