The study was performed in the Cardiovascular Surgery department of the Georges Pompidou European Hospital (HEGP), a university teaching hospital in Paris, France. The hospital has 806 beds organized around 3 major medical departments: cardiovascular, cancer and internal medicine, and an emergency center. There are approximately 204,000 consultations and 55,000 admissions per year. Cardiac surgery and transplantation constitute an important part of its activity.

Since opening in 2000, the hospital has used an entirely computerized HIS centered on DxCare^® an industry EHR 15. The EHR facilitates the computerized prescription of drugs, imaging and laboratory tests by means of a CPOE. Every test order is made through the CPOE by a physician on the house staff. The order is immediately visible on the nursing care plan. It is transmitted in parallel to the laboratory software, which records that a laboratory sample will be sent to the lab. DxCare^® also permits the viewing of laboratory results. By default, the results shown are those for the current patient stay in the hospital, which means that a physician who wants information from previous stays has to actively search for it. During year 2005, among the 1669 viral serology tests ordered for patients hospitalized in the cardiovascular surgery department, 280 (17%) were ordered within 90 days after a previous such test for the same patient and were considered unnecessary by the resource utilization committee of the hospital.

In this study, viral serology testing is defined in screening protocols for hepatitis B virus (HBV), associated or not with hepatitis C virus (HCV). Serological tests for HBV, either in isolation or with other viral serology tests, are the most frequently ordered viral serology tests. The protocol for HBV testing involves the simultaneous prescription of three individual tests; only one of those, the test for HBs antigen, is carried out systematically. The other two tests, for antibodies against HBs and HBc, are carried out only if the HBs antigen is detected. The evaluation was therefore solely based on the data analysis of HBV tests, and especially HBs antigen tests.

The resource utilization committee of the hospital defined a serology test as unnecessarily repeated if the order occurred within 90 days from the previous result. The 90 day period was chosen because it corresponds to the mean incubation period of the disease.

The Serology-CDSS is triggered when one of the targeted serological tests for HBV is selected to be ordered (Figure 1 - steps 1 & 2A). The Serology-CDSS stores a record of its execution each time a physician selects a viral serology test order (Figure 1 - step 3), ie, each time the physician intends to order that test. The system takes into account the most recent laboratory results for viral serology tests listed in the patient's EHR and their dates, regardless of their relationship to the current stay (Figure 1 - step 4). An alert is displayed if the most recent result of the targeted laboratory test for the patient is less than 90 days old (Figure 1 - step 5). Conversely, if no result is available or if the last available result was more than 90 days old, no alert is displayed. The Serology-CDSS displays a new HTML page concomitant with the order entry window (Figure 1 - steps 2 & 5). The alert informs the user of the date and complete result of the last serological test carried out for the patient (Figure 2). The alert is displayed only to prescribers who are members of the house staff.

The Serology-CDSS has been developed to include four technical characteristics known to be associated with decision support systems success 3416: the alert was automatically prompted and was part of clinician workflow, the user could not deactivate the alert output, the most recent laboratory result for viral serology tests and its date was automatically retrieved from the patient's EHR, and the alert was displayed at the time and location of decision making (ie, before the user ordered an unnecessarily repeated test).

We evaluated the effect of the intervention by analyzing the time series of the monthly proportion of repeated HBs antigen tests 17. The Serology-CDSS became functional in the Cardiovascular Surgery department in June 2006; several modifications were made up to the end of November 2006. As recommended 181920, we collected data from 2004 to 2007 to have sufficient points before and after the start of the intervention to account for seasonally correlated errors. June 2006 was excluded from analysis because the intervention was initiated mid-month. Three periods were defined: the pre-intervention period (January 2004 to May 2006), the adjustment period (July 2006 to November 2006) and the effective intervention period (December 2006 to December 2007).

We used a segmented regression analysis to determine the impact of the intervention, both immediately (change in level) as well as over time (change in trend) 1821. The full segmented regression model included a baseline trend, a change in level and trend after the start of the intervention (July 2006), and a change in level and trend after the adjustment period (December 2006). The most parsimonious model was obtained after eliminating non-significant terms using a backward selection. Our final model did not include correction for seasonal variation (not detected), nor adjustment for autocorrelation (residuals were independent, normally distributed with mean zero and constant variance). In a similar way, we compared the change in level and trend between periods for characteristics of patients (sex ratio, age) and hospital stays (frequency of stays with transplant, length of stay) using four segmented regression models (time series data not shown). We identified patients and hospital stays for a period according to the first HBs antigen test in the Cardiovascular Surgery department.

SAS statistical software (release 9.1; SAS Institute Inc., Cary, NC, USA) was used for all analyses.

According to French laws, this study did not required to be approved by an ethical committee, since it concerned the improvement of quality of care and routine practice.

During the study period (June 2006 excluded) 4,415 patients had at least one HBs antigen test in the Cardiovascular Surgery department (5,412 hospital stays). Characteristics of patients and hospital stays according to period are presented in table 1. 3,132 (70.9%) patients were male and the median age was 64 (interquartile range [IQR], 53 to 74). 85 (1.6%) hospital stays concerned transplanted patients and median length of stay was 10 days (IQR, 5 to 16). According to the segmented regression analysis, the sex ratio and median age of patients did not change during the study period (no significant level or trend change between the three periods). However, there was an increase of stays with transplant during the pre-intervention period and a significant decrease of length of stay during the effective intervention period (trend change).

A total of 5,575 HBs antigen tests were ordered in the Cardiovascular Surgery department during the study (June 2006 excluded). In the pre-intervention period, 3,480 tests were ordered, of which 538 (15.5%) were unnecessarily repeated. For 11.2% of them (60/538), at least three such tests were ordered for the patient. During the intervention period, 2,095 HBs antigen tests were performed, with 330 unnecessary repetitions (15.8%): 99 (15.6%) when the CDSS was in the adjustment period and 231 (15.8%) during the effective intervention period. 14.6% of the repeated tests (48/330) were the third or more test ordered for the patient.

Among the 868 unnecessarily repeated tests, 865 were done when previous serology test result was negative and 3 when the result was positive. The percentage of accepted messages was higher when the previous serology test result was positive: 86.4% (19/22) versus 48.2% when the previous test was negative (805/1670) (p < 0.001).

During the study period, 31.0% (27/87) of patients with hospital stays for transplant had an unnecessary repetition of viral serology tests versus 15.4% (844/5482) for other stays. In the pre-intervention and intervention periods respectively, 10 of 538 (1.9%) and 23 of 330 (7.0%) unnecessarily repeated tests occurred for transplant stays.

Figure 3 shows the time series of the proportions of unnecessarily repeated HBs antigen tests from January 2004 to December 2007. Segmented regression analysis revealed a significant month-to-month change before the beginning of the CDSS integration. Before June 2006, the mean proportion of unnecessarily repeated HBs antigen tests was estimated at 9.0% per month (95% CI 6.6% to 11.3%) and increased by 0.4% per month (absolute increase, 95% CI 0.2% to 0.6%, p < 0.001).

There were no significant differences in level or in trend change between the two sub-periods of the intervention (adjustment period and effective intervention period). In June 2006, the estimated mean proportion of HBs antigen tests dropped by 4%. A significant trend change occurred with a monthly difference of -0.4% (95% CI -0.7% to -0.1%, p = 0.02) compared to the trend of the pre-intervention period. This resulted in a stable unnecessarily repeated test rate during the intervention period (non-significant reduction of 0.02%, p = 0.87).

During the intervention period (adjustment period and effective intervention period), the Serology-CDSS was triggered 7,342 times for all serological test orders combined and 2,600 times for HBV test orders. Five hundred alerts were displayed for potentially redundant HBV tests, and 380 unnecessary tests were ordered despite the alerts (compliance rate 24%).