Computerized Alert Reduced D-Dimer Testing in the Elderly

A targeted computerized alert at the time of physician order entry reduced the use of D-dimer testing among patients 65 years and older.

Published Online: November 04, 2010
Ted E. Palen, PhD, MD, MPSH; David W. Price, MD; Aaron J. Snyder, MD; and Susan M. Shetterly, MS

Objective: To assess the effect of a targeted age-specific computerized alert to reduce D-dimer testing in elderly patients.


Study Design: A single-crossover cluster randomized trial of computerized alerts during physician order entry involving 8 ambulatory care clinics in a group-model integrated care delivery system.


Methods: The rate of completed D-dimer tests per 1000 patient visits, ratio of completed venous ultrasonography to completed D-dimer tests, and rate of completed venous ultrasonography per 1000 patient visits.


Results: The rate of completed D-dimer tests per 1000 visits among patients 65 years and older in intervention clinics decreased from 5.02 to 1.52 (95% confidence interval [CI], -4.20 to -2.80;P <.001), which persisted throughout the study period. The rate of completed D-dimer tests per 1000 visits among patients 65 years and older in control clinics decreased from 3.14 to 2.11 (95% CI, -1.66 to -0.04; P <.001 for interaction). After activation of the alert in control clinics, the rate of completed D-dimer tests per 1000 visits among patients 65 years and older decreased from 2.11 to 0.81 (95% Cl, -1.79 to -0.80; P <.001). After activation of the alert in each clinic group, the ratios of completed venous ultrasonography to completed D-dimer tests increased from 1.17 to 4.05 (95% CI, 2.52-3.22) and from 2.25 to 7.29 (95% CI, 3.74-6.35) in intervention clinics and control clinics, respectively (P <.001 for both).


Conclusion: An electronic age-specific alert targeted to a specific condition reduced D-dimer testing in this elderly population of outpatients and demonstrated a persistent effect.


(Am J Manag Care. 2010;16(11):e267-e275)

Physicians often find it difficult to remember to follow evidence-based clinical practice guidelines. Many researchers have suggested that computer-generated alerts within electronic medical records may serve as reminders to improve adherence to best practices. However, too many alerts produce alert fatigue and may lead physicians to ignore them. Our study shows that an alert targeted to a specific order and for specific patients can alter a physician's ordering behavior and promote improved adherence to a clinical practice guideline.


  • A targeted computerized alert reduced the use of D-dimer testing in elderly patients.
  • An alert targeted to a specific condition demonstrated a persistent effect.
  • Computerized alerts should contain alternative diagnostic or treatment strategies to direct clinicians toward more appropriate diagnostic strategies rather than just provide "negative guidance."
The risk of developing a blood clot in the venous circulation increases exponentially with age from approximately 30 cases per 100,000 persons aged 25 to 35 years to 300 to 500 cases per 100,000 persons aged 70 to 79 years.1 Rates of pulmonary embolism (PE) increase from 120 per 100,000 persons aged 65 to 69 years to approximately 700 per 100,000 persons 85 years and older; about half of all deaths after venous thromboembolism (VTE) are attributed to PE.2,3 Venous thromboembolism most commonly includes deep vein thrombosis (DVT) or PE. Symptoms common to PE and DVT appear in various clinical conditions. Clinical diagnosis of suspected acute VTE is difficult. Therefore, objective testing combined with a clinical risk algorithm is recommended.4-7

Since the late 1980s, high-resolution venous ultrasonography has become widely used to diagnose or exclude DVT in most community practices throughout the United States.7-9 In the early 1980s, a quantitative D-dimer test based on enzyme-linked immunosorbent assay (ELISA) was introduced as a means to exclude acute VTE. Investigators have studied the role of D-dimer in the diagnosis of DVT and PE.10-12 Controlled studies13-17 using a sensitive automated ELISA D-dimer assay have shown that D-dimer levels below an established cutoff of 500 ng/mL combined with a clinical risk algorithm enable exclusion of acute venous thrombosis in up to 30% of outpatients (to convert D-dimer level to nanomoles per liter, multiply by 5.476). However, the negative predictive value of the test worsens as patient age increases.18-21 Although the sensitivity and the negative predictive value of the test are about 98%, the specificity is less than 30%, and the overall accuracy of the test is only 35% for patients 65 years and older.22-24 Previously, our group demonstrated that more of these tests are ordered in clinical practices where D-dimer testing is readily available.24 In real-world experience, it was found that more than 73% of all D-dimer tests among patients 65 years and older had positive results, and almost 65% of these were false positives that required additional radiologic evaluation. Only about 27% of all D-dimer tests performed among the elderly had negative results; therefore, only these patients avoided additional radiologic procedures. In comparison, among patients younger than 65 years, the test had a negative predictive value exceeding 99%, a specificity exceeding 70%, and an overall accuracy exceeding 70%.

In 2007, the American Academy of Family Physicians and the American College of Physicians25 jointly published a guideline onthe diagnosis of lower extremity DVT and PE, which recommended the use of clinical prediction rules to establish pretest probability of disease and advised using D-dimer testing to exclude VTE in younger patients without associated comorbidity or history of VTE. However, the guideline notes that D-dimer testing may be insufficient to rule out VTE in older patients.26 Other researchers also present evidence supporting that older patients should not receive D-dimer testing and recommend that an alternative strategy based on noninvasive examinations such as venous ultrasonography should be the first choice for evaluation of possible DVT.9,26-28

In 2001, Kaiser Permanente of Colorado adopted the quantitative D-dimer test for use in clinical practice. Since then, the number of D-dimer tests ordered for patients 65 years and older has increased 5-fold, accounting for about one-third of all D-dimer tests ordered. The convenience of ordering a laboratory test and of potentially avoiding a trip by the patient to a diagnostic radiology center may be partially fueling the increased use of the D-dimer test. However, because of the quantity of tests being ordered in patients 65 years and older and owing to poor test performance in this age group, we have also seen a significant increase in the number of positive D-dimer test results, which required additional testing using radiologic evaluation. Most positive D-dimer test results in the elderly (65%) were determined to be false positives on further evaluation of patients’ venous ultrasonography results.24 Therefore, we wondered whether a computerized alert within the physician order entry module of the electronic medical record (EMR) that we use (Kaiser Permanente HealthConnect [KPHC]; Epic Systems, Verona, Wisconsin) could reduce the number of D-dimer tests ordered for elderly patients. We hypothesized that computergenerated reminders given to primary care providers at thetime of ordering a D-dimer test for patients 65 years and older for suspected VTE would decrease the rate of D-dimer test ordering among providers receiving the alert compared with providers not receiving the alert. This article reports our results of a randomized controlled study using this alert within a group-model health maintenance organization using an EMR for documentation and order entry of all outpatient clinical care.


Between September 2005 and October 2007, we performed an internally funded cluster randomized trial involving 8 ambulatory care clinics in a group-model integrated care delivery system in Denver, Colorado. The institutional review board of Kaiser Permanente of Colorado approved the study before the start. This research did not require contact with study subjects (physicians or patients). Data used were retrospective and were extracted in a deidentified format before analysis began. This trial began before July 1, 2008, and did not require trial registration to meet guidelines of the International Committee of Medical Journal Editors.

Participant Selection and Randomization

We identified 8 primary care clinics, each with at least 3000 patients 65 years and older. We performed a simple cluster randomization to assign half of the clinics to a control group and the other half to an intervention group. A cluster randomized design was selected to decrease the risk of interprovider contamination among providers within the same facility. Primary care providers within the designated clinics were unaware that a research study was occurring in regard to D-dimer test ordering related to the alerts.


All primary care providers received training and information about the use of clinical risk algorithms for patients with suspected venous thrombosis and about the performance characteristics of the D-dimer test among various age groups.23,24 This training took place during one of the monthly continuing medical education meetings for primary care providers 4 months before the intervention. Primary care providers in intervention clinics also saw the following pop-up alert within the physician order entry system at the time of placing a computerized D-dimer test order for patients 65 years and older, advising against ordering the D-dimer test: “D-dimer testing is not recommended for patients 65 years

of age and over because the accuracy is only 35% in this age group. Instead, order diagnostic imaging as appropriate.” Providers in control clinics did not receive this alert during the initial intervention. After 20 months, the alert was activated in control clinics; it remained active in intervention clinics.The specific metrics for each step of the project are shown in Figure 1.

Data on D-dimer tests and venous ultrasonography among patients having office visits in intervention clinics and control clinics were collected before and after activation of the alert. Data included clinic site, date of D-dimer order and result, and date of radiology test (Current Procedural Terminology code 93971 [ultrasonography of extremities]) and result after a D-dimer test. Except for patient age, other patient characteristics were unavailable in the data sets used for analyses.

Outcome Measurements

The primary outcome measure was the number of D-dimer tests ordered and completed per 1000 patient visits (including all office visits for all patients in each age group for each clinic). This rate excluded D-dimer tests that occurred within 14 days of each other for the same patient. The secondary outcome measure, the effect on ultrasonography ordering for evaluation of DVT, was assessed by determining the ratio of completed venous ultrasonography to completed D-dimer tests and the rate of completed venous ultrasonography per 1000 patient visits for each age group.

Statistical Analysis

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