Laboratory test ordering at physician offices with and without on-site laboratories.

Background: Physician self-referral, ordering a test or procedure or referring to a facility in which a physician has a financial interest, has been associated with increased utilization of health care services.

Objective: To examine the association between on-site laboratories and laboratory test ordering among visits to group-practice physicians.

Methods: Cross-sectional study using data from the 2005 and 2006 National Ambulatory Medical Care Surveys. Methods: Visits by adults to non-federally-funded, non-hospital-based group practices. Primary analyses focused on visits to physician owners; secondary analyses focused on visits to non-owners. Methods: Ordering of five laboratory tests: complete blood count (CBC), electrolytes, glycoslyated hemoglobin A1c (HbA1c), cholesterol, and prostate-specific antigen (PSA).

Results: There were 19,163 visits to group-practice owners with 51.9% to a practice with an on-site laboratory. Visits to primary care physicians were more likely to be to a practice with an on-site laboratory when compared with visits to specialists (64.4% vs. 34.0%, p < 0.001). Among visits to specialist group owners, all five tests were ordered more often if there was an on-site laboratory, even after accounting for patient and practice characteristics: CBC: adjusted odds ratio[OR] = 8.01, 95% Confidence Interval [CI], 5.00-12.82, p < 0.001; electrolytes: aOR = 3.51, 95% CI, 1.93-6.40, p < 0.001; HbA1c: aOR = 4.91, 95% CI, 1.75-13.78, p = 0.003; cholesterol: aOR = 3.32, 95% CI, 1.85-5.93, p < 0.001; and PSA: aOR = 3.84, 95% CI, 1.93-7.65, p < 0.001. This association was not found among visits to primary care physician owners and all practice non-owners (both primary care and specialists). The estimated excess spending on these five tests by specialist owners with on-site laboratories was $75 million per 100 million visits.

Conclusions: In a nationally representative sample of visits to physician-owned group practices, specialist owners with on-site laboratories were more likely to order five common laboratory tests, potentially resulting in millions in excess healthcare spending.