Are rates of pathology test ordering higher in general practices co-located with pathology collection centres?

Objective: To determine whether rates of pathology test ordering by general practitioners in general practices co-located with pathology collection centres (PCCs) are higher than those of GPs in practices located apart from PCCs.

Design, Setting And Participants: We identified all practices in the Melbourne and Sydney metropolitan areas that were co-located with PCCs (same or immediately adjacent suite) and the date co-location was established. This information was merged with the Bettering the Evaluation and Care of Health database to identify samples of GP-patient encounters in co-located practices (n = 31,700) and practices located apart from the nearest PCC (n = 289,700) over the period 2000-2009. Using Poisson regression analysis and logistic regression analysis, we compared GP test-ordering rates across the two types of practices, controlling for a range of potential confounders.

Main Outcome Measures: Numbers of tests ordered per encounter; likelihood of ordering one or more tests per encounter.

Results: In unadjusted analyses, GPs in co-located practices ordered more pathology tests than GPs in practices located apart from PCCs (40.3 v 37.0 tests per 100 encounters, P = 0.01) and had a higher likelihood of ordering one or more tests (16.8% v 15.5% of encounters, P < 0.01). After adjusting for other predictors of test ordering, however, neither test-ordering rate (rate ratio, 0.98; 95% CI, 0.93-1.05; P = 0.56) nor likelihood of ordering one or more tests per encounter (odds ratio, 1.01; 95% CI, 0.95-1.07; P = 0.79) differed significantly by co-location status. Sub-analyses within specific test groups and types showed few systematic differences.

Conclusions: Pathology test-ordering rates are not higher in practices co-located with PCCs. To the extent inappropriate commercial influences and relationships exist in the pathology sector, GPs' test-ordering behaviour may be unaffected.