Physician and practice characteristics associated with immunoglobulin test ordering

Sharon L Cadogan, John P Browne, Colin P Bradley, Anthony P Fitzgerald, Mary R Cahill

Primary care test requests for serum immunoglobulins are rising rapidly, with concerns that many requests may be unnecessary. Evidence suggests some characteristics of general practitioners (GPs) and practices are associated with higher test ordering. To identify the physician and practice characteristics associated with immunoglobulin test ordering. Retrospective, cross-sectional study using routine laboratory data on primary care serum immunoglobulin requests. Data were linked with GP patient list size data. The primary outcome measure was the count of test requests per GP. Predictor variables were physician gender, years experience, practice region and type (number of GPs), GP patient list size and composition. Mixed-effects multilevel regression models were used to calculate incidence rate ratios (IRRs) with 95% confidence intervals (CIs) for the associations between physician and practice characteristics and GP requesting. Sensitivity analysis was performed by limiting the model to the more than 70 years age category. In total, 5990 immunoglobulin tests were ordered by 481 GPs in the South of Ireland during 2013. The number of tests ordered by individual GPs varied from one to 377. In the final fully adjusted Poisson regression analysis, female gender (IRR: 1.81; 95% CI: 1.45-2.26) and less experience (IRR: 2.27; 95% CI: 1.47-3.51) were associated with higher requesting (P < 0.001). None of the practice factors were associated with test ordering. Sensitivity analysis on the 70 years or more age category found similar results. Further research is required to explore the potential reasons for higher requesting among GPs with fewer years of experience and also among female GPs.