Study Objective: To determine the effect of displaying previous results of diagnostic tests on the ordering of selected outpatient tests.
Design: Sixteen-week controlled trial with a 13-week preintervention and 8-week post-intervention observation periods. Patients were randomly assigned to intervention or control groups so that each physician was his or her own control. Only scheduled visits were included. Randomization occurred before the pre-intervention observation period.
Setting: Academic primary care general medicine clinic affiliated with an urban general hospital.
Subjects: Pre-intervention period: 111 physicians (97 internal medicine residents, 14 faculty internists), 4683 patients, 5942 scheduled visits. Intervention period: same 111 physicians, 5946 patients, 8148 visits. Post-intervention period: 76 physicians (62 residents, 14 faculty), 2571 patients, 2858 scheduled visits.
Intervention: When physicians ordered one of eight selected diagnostic tests through microcomputer workstations, a window was opened on the screen and previous test results were displayed along with the time interval between the first and last result. Tests were ordered for control patients into the same workstations without previous results displayed.
Measurements and Main Results: Previous results of one or more study tests were available for display for 96% of scheduled patients. Significantly lower results (p < 0.05 by paired t-test) for the selected tests were found for scheduled-intervention patient visits than for control visits: charges per visit (mean ± SE) for intervention patients $12. 17 ± 0.62, compared with $13.99 ± 0.77 for controls, a 13.0% difference; tests per visit were 0.51 ± 0.03, compared with 0.56 ± 0.03, an 8.5% difference compared with the preintervention period. The number of study tests ordered during the intervention period decreased significantly for intervention patients (16.8%) and for controls (10.9%). During the post-intervention period, ordering of study tests increased for both groups, but the increase from the intervention period was not significant.
Conclusions: Presenting physicians with previous test results reduced the ordering of those tests. The actual effect may have been greater than 13%, because there were reductions in study tests ordered for both intervention and control patients during the intervention period when compared with the pre-intervention period, and both tended to rise after the intervention, or display, was turned off.