Laboratory test use and primary care physician supply.

OBJECTIVE To determine the relative effects of population size, FP and GP supply, and other specialist supply on chemistry and hematology test volumes (ie, number of tests performed). DESIGN Population-level analysis using secondary data from the Calgary Health Zone for 2004 to 2009. SETTING Calgary, Alta. MAIN OUTCOME MEASURES The relative effects of population size, FP and GP supply, and other specialist supply on laboratory test use. RESULTS Population size was the strongest predictor of test volumes in a multivariate analysis. The FP and GP supply was significantly negatively correlated with chemistry test volume (partial r(2) = 0.186, P = .045). There was a trend toward decreasing use of hematology tests with increasing FP and GP supply (partial r(2) = 0.117, P = .119). CONCLUSION The relationship between FP and GP supply and laboratory test use is complex, but increasing numbers of FPs do not necessarily indicate an increase in laboratory test use and might be associated with a decrease in test use when other factors are controlled for.