Variation in test ordering behaviour of GPs: professional or context-related factors?

Objective. The aim of this study was to describe GPs' test ordering behaviour, and to establish professional and context-related determinants of GPs' inclination to order tests. Methods. A cross-sectional analysis was carried out of 229 GPs in 40 local GP groups from five regions in The Netherlands of the combined number of 19 laboratory and eight imaging tests ordered by GPs, collected from five regional diagnostic centres. In a multivariable multilevel regression analysis, these data were linked with survey data on professional characteristics such as knowledge about and attitude towards test ordering, and with data on context-related factors such as practice type or experience with feedback on test ordering data. The main outcome measure was the percentage point differences associated with professional and context-related factors. Results. The total median number of tests per GP per year was 998 (interquartile range 663-1500), with significant differences between the regions. The response to the survey was 97%. At the professional level, 'individual involvement in developing guidelines' (yes versus no), and at the context-related level 'group practice' (versus single-handed and two-person practices) and 'more than 1 year of experience working with a problem-oriented laboratory order form' (yes versus no) were associated with 27, 18 and 41% lower numbers of tests ordered, respectively. Conclusion. In addition to professional determinants, context-related factors appeared to be strongly associated with the numbers of tests ordered. Further studies on GPs' test ordering behaviour should include local and regional factors