An age-adapted approach for the use of D-dimers in the exclusion of deep venous thrombosis

D-dimer - a multifaceted molecule

D-dimer, a universally unique marker for fibrin degradation, is generated through the enzymatic interplay of thrombin, factor XIIIa, and plasmin. The emergence of D-dimer-containing fibrin molecules occurs in both intravascular and extravascular spaces during pivotal physiological processes like haemostasis, thrombosis, and tissue repair. Given the inherently physiological nature of fibrin formation and fibrinolysis, basal levels of D-dimer fragments are present in plasma. Beyond its role as a marker of routine physiological processes, aberrations in D-dimer levels are indicative of a spectrum of conditions, both non-pathological and pathological. The clinical utility of D-dimer has been firmly established, particularly in scenarios like venous thromboembolism (VTE), pulmonary embolism (PE), deep vein thrombosis (DVT), and disseminated intravascular coagulation (DIC). Additionally, recent applications have extended to assess the prognosis of COVID-19. While D-dimer is commonly associated with thrombotic conditions, its elevation is not confined to these conditions alone. Elevated D-dimer levels are observed across various diseases, where its significance extends beyond diagnostic indicators to prognostic implications.

Deep vein thrombosis and its risk factors in neurodegenerative diseases: A markedly higher incidence in Parkinson's disease

BACKGROUND

Information on the incidence and risk factors of deep vein thrombosis (DVT) in neurodegenerative diseases is limited. We aimed to determine the incidence of DVT among neurodegenerative disorders (amyotrophic lateral sclerosis [ALS], Parkinson's disease [PD], multiple system atrophy [MSA], and progressive supranuclear palsy [PSP]-corticobasal syndrome [CBS]) and the risk factors for the development of DVT.

METHODS

Overall, 229 hospitalized patients with neurodegenerative diseases (65 patients with ALS, 61 with PD, 53 with MSA, and 50 with PSP-CBS) were included in this study. D-dimer value and ultrasonography of the leg vein were assessed to determine the presence or absence of leg DVT. We compared the DVT incidence among each disease group. To identify the risk factors for DVT, a multivariate analysis was performed.

RESULTS

Of 229 patients, 34 had leg DVT; the incidence was significantly higher in patients with PD (38%) than in those with ALS (2%), MSA (5%), or PSP-CBS (4%). Patients with DVT were older, had a smaller waist circumference, had a longer disease duration, and had a high blood pressure (BP) variability. Multivariate analysis revealed that a PD diagnosis and female sex, with a high BP variability were predictive of leg DVT.

CONCLUSIONS

Among the neurodegenerative diseases, the DVT incidence was markedly higher in PD than in ALS, MSA, and PSP-CBS. Several risk factors have been identified in patients with leg DVT. Recognition of these risk factors will improve patient care and guide the appropriate use of anticoagulants.

Unprovoked Venous Thromboembolism: The Search for the Cause

Venous thromboembolism (VTE) is a common vascular disorder encompassing deep vein thrombosis (DVT) and pulmonary embolism (PE). There is no data on global estimates of VTE prevalence and incidence. Most patients with unprovoked VTE require secondary thromboprophylaxis upon the completion of the primary treatment phase if they have no high bleeding risk. Risk prediction models can help identify patients at low VTE recurrence risk who may discontinue anticoagulation upon the completion of the primary treatment phase.

How to Combat Over-Testing for Patients Suspected of Pulmonary Embolism: A Narrative Review

The diagnosis of PE remains difficult in 2023 because the signs and symptoms are not sensible nor specific. The consequences of potential diagnostic errors can be dramatic, whether by default or by excess. Furthermore, the achievement of a simple diagnostic strategy, based on clinical probability assessment, D-dimer measurement and computed tomography pulmonary angiography (CTPA) leads to a new challenge for PE diagnosis: over-testing. Indeed, since the 2000s, the wide availability of CTPA resulted in a major increase in investigations with a mod I confirm erate increase in PE diagnosis, without any notable improvement in patient outcomes. Quite the contrary, the complications of anticoagulation for PE increased significantly, and the long-term consequences of imaging diagnostic radiation is an important concern, especially the risk of breast cancer for young women. As a result, several strategies have been proposed to fight over-testing. They are mostly based on defining a subgroup of patients for whom no specific exam should be required to rule-out PE and adjusting the D-dimer cutoff to allow the exclusion of PE without performing CTPA. This narrative review presents the advantages and limitations of these different strategies as well as the perspective in PE diagnosis.

Factors affecting D-dimer levels in patients with uncomplicated primary varicose veins

Objectives The diagnosis of deep venous thrombosis (DVT) is hampered in patients with primary varicose veins due to similarity of symptoms of DVT and PVV and elevated levels of D-dimers. The purpose of this study was to analyze factors that influence the D-dimer concentration in patients with PVV in order to redefine its diagnostic value. Methods Forty- one patients with non-complicated PVV were enrolled in the study, in whom D-dimer level was determined by immunoturbidimetric assay. The influence of selected clinical factors on the concentration of D-dimers was determined with univariate and bivariate analysis. Besides descriptive statistics the D-dimers levels were compared to the age -adjusted cutoff values. Results The median concentration of D-dimer was 630.0 ng/ml (440.0-1140.0 ng/ml) and was above the age-adjusted level in 21 (52%) of patients. There was a positive correlation between the patient's age and and D-dimer concentration (p = 0.035, Spearman correlation coefficient rs=0,33. The bivariate analysis showed a significant interaction between age and weight p=0,02. Conclusions In patients with PVV the diagnostic value of D-dimers is limited especially in older and overweight subjects.

Age-adjusted D-dimer cut-off levels to rule out venous thromboembolism in patients with non-high pre-test probability: Clinical performance and cost-effectiveness analysis

BACKGROUND

As aging was found to be associated with increased D-dimer levels, the question arose whether D-dimer measurement was useful in the diagnostic strategy of venous thromboembolism (VTE) in elderly patients.

AIM OF THE STUDY

To compare retrospectively the performance of six diagnostic strategies based on the three-level Wells scores and various cut-off levels for D-dimer, evaluated using the HemosIL D-Dimer HS 500 assay, in a derivation cohort of 644 outpatients with non-high pretest probability (PTP) of VTE. The clinical usefulness of the best-performing strategy was then confirmed in a multicenter validation study involving 1255 consecutive outpatients with non-high PTP.

RESULTS

The diagnostic strategy based on the age-adjusted cut-off level calculated by multiplying the patient's age by 10 above 50 years was found to perform the best in the derivation study with a better sensitivity-to-specificity ratio than the conventional strategy based on the fixed cut-off level (500 ng/ml), a higher specificity and a negative predictive value (NPV) above 99%. Such an increase in test specificity was confirmed in the validation cohort, with the NPV remaining above 99%. Taking into account the local reimbursement rates of diagnostic tests, using this strategy led to a 6.9% reduction of diagnostic costs for pulmonary embolism and a 5.1% reduction for deep vein thrombosis, as imaging tests would be avoided in a higher percentage of patients.

CONCLUSION

The diagnostic strategy of VTE based on the age-adjusted cut-off level for D-dimer in patients over 50 years was found to be safe, with NPV above 99%, and cost-effective.

Venous thromboembolism: A clinician update

Venous thromboembolism (VTE) is a common vascular condition. New medications are available to prevent hospital-associated VTE. Strategies are being studied to increase appropriate diagnostic testing utilization. Management of deep vein thrombosis (DVT) and pulmonary embolism (PE) has evolved with the advent of new anticoagulant options and catheter-directed intervention. In light of this, providers are commonly challenged with the decision regarding inpatient versus outpatient management. Which patients require long-term (> 3 months) anticoagulation is challenging and multiple clinical prediction models may be used to help determine the risk-benefit ratio in each patient. The management of VTE is an ongoing area of research and is rapidly evolving.

Can the use of an age-adjusted D-dimer cut-off value help in our diagnosis of suspected pulmonary embolism?

Safe exclusion of pulmonary embolism (PE) is a common problem in acute medicine. Common care pathways usually involve the use of a pre-test probability score with a D-dimer test to aid clinical decision-making. Unfortunately, the specificity of many D-dimer assays decreases with age. This study investigates the role of an age-adjusted D-dimer of 5 x patient's age when the conventional cut-off of the assay is 230 ng/mL. Data was collected retrospectively over a 12-month period from patients who went on to have either computed tomography pulmonary angiography (CTPA) or pulmonary ventilation/perfusion (V/Q) imaging. D-dimers in patients with low or moderate Wells score were analysed for both conventional and age-adjusted cut-offs. The use of an adjusted D-dimer showed a sensitivity of 0.97 (95% CI 0.9-1.0) while the specificity increased from 0.07 (95% CI 0.04-0.11) for the conventional cut-off to 0.32 (95% CI 0.27-0.38) for the age-adjusted cut-off. Using a 5 x patient's age-adjusted D-dimer cut-off is both safe and showed an increased specificity comparable to those published previously on other D-dimer assays.

Age-adjusted D-dimer for the diagnosis of deep vein thrombosis

Objective In the diagnosis of deep vein thrombosis, new D-dimer cut-off values were defined by multiplying 10 µg/L × age. The objective of the present study is to define a more specific age-adjusted value, including the pre-test Wells score, without worsening sensitivity. Methods We designed a case-control study in patients attended in the emergency department with clinically suspected deep vein thrombosis. Demographics, Wells score, D-dimer and ultrasound data were collected. In low and intermediate clinical probability cases for deep vein thrombosis, we determined the specificity and sensitivity (false-negative rates) for the following cut-off values of D-dimer: age × 10 µg/L, age × 15 µg/L, age × 20 µg/L, age × 25 µg/L and age × 30 µg/L. The cut-off value with maximum specificity without any false-negative result (sensitivity 100%) was identified. Results We included 138 consecutive patients, 39.9% were men and the mean age was 71.6 years. Deep vein thrombosis was diagnosed in 16.7% of patients and the Wells score was low in 69.6%, intermediate in 21% and high in 9.4% of patients. Applying the conventional cut-off value of 500 µg/L, the specificity was 21.1% with a sensitivity of 100%. Maintaining 100% sensitivity, the highest specificity was reached with a cut-off value for D-dimer equivalent to the age × 25 µg/L in low-risk patients (67.1% specificity) and the age × 10 µg/L (50% specificity) in intermediate-risk patients. Conclusions In patients with low Wells score, the cut-off value can be raised to age × 25 µg/L in order to rule out deep vein thrombosis without jeopardizing safety. In intermediate-risk patients, the D-dimer cut-off value could be raised to age × 10 µg/L as previously suggested.

A systematic review of clinical prediction scores for deep vein thrombosis

Objective Diagnosis of deep vein thrombosis remains a challenging problem. Various clinical prediction rules have been developed in order to improve diagnosis and decision making in relation to deep vein thrombosis. The purpose of this review is to summarise the available clinical scores and describe their applicability and limitations. Methods A systematic search of PubMed, MEDLINE and EMBASE databases was conducted in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidance using the keywords: clinical score, clinical prediction rule, risk assessment, clinical probability, pretest probability, diagnostic score and medical Subject Heading terms: 'Venous Thromboembolism/diagnosis' OR 'Venous Thrombosis/diagnosis'. Both development and validation studies were eligible for inclusion. Results The search strategy returned a total of 2036 articles, of which 102 articles met a priori criteria for inclusion. Eight different diagnostic scores were identified. The development of these scores differs in respect of the population included (hospital inpatients, hospital outpatients or primary care patients), the exclusion criteria, the inclusion of distal deep vein thrombosis and the use of D-dimer. The reliability and applicability of the scores in the context of specific subgroups (inpatients, cancer patients, elderly patients and those with recurrent deep vein thrombosis) remains controversial. Conclusion Detailed knowledge of the development of the various clinical prediction scores for deep vein thrombosis is essential in understanding the power, generalisability and limitations of these clinical tools.

Performance Evaluation of Different d-Dimer Cutoffs in Bedridden Hospitalized Elderly Patients

A rapid and accurate diagnosis of venous thromboembolism (VTE) in the elderly individuals represents a dilemma due to nonspecific clinical presentation, confusing laboratory results, and the hazards of radiological examination in this age-group. d-Dimer test is used mainly in combination with non-high clinical pretest probability (PTP) to exclude VTE. d-Dimer testing retains its sensitivity, however, its specificity decreases in the elderly individuals. Raising the cutoff level improves the specificity of the d-dimer test without compromising its sensitivity. The current study aimed to explore the reliability of higher d-dimer cutoff values for the diagnosis of asymptomatic VTE in a population of bedridden hospitalized elderly patients with non-high clinical PTP. This retrospective study included 252 bedridden hospitalized elderly patients (>65 years) who were admitted to the Ain shams University Specialized Hospital with non-high clinical probability and developed later reduced mobility; all underwent quantitation of d-dimer and Doppler examination. Considering the whole population (>65 years), the age-adjusted cutoff achieved the best performance in comparison with the conventional and receiver operating characteristic (ROC)-derived cutoffs. When stratified according to age, the age-adjusted cutoff showed the best performance in the age-group 65-70 and comparable performance with the ROC-derived cutoff in the age-group 71-80, however, its sensitivity compromised in those older than 80 years. In conclusion, it is recommended to use age-adjusted cutoff value of d-dimer together with the clinical probability score in elderly individuals (65-80 years).

Comparison of five D-dimer reagents and application of an age-adjusted cut-off for the diagnosis of venous thromboembolism in emergency department

There is still a considerable uncertainty concerning D-dimer cut-off values used in exclusion of venous thromboembolic (venous thromboembolism, VTE) disease, especially among the elderly patients. The objectives were to compare five different D-dimer reagents in the daily practice of an emergency department and to test retrospectively the performances of an age-adjusted cut-off. A total of 473 consecutive ambulatory outpatients suspected of VTE (confirmed VTE = 21) were included in this study. Five commercially available tests were assessed: STA-Liatest D-Di (LI), AxSYMD-Dimer (AX), VIDAS D-Dimer (VI), INNOVANCE D-Dimer (IN), and HemosIL D-Dimer HS (HS). When using a cut-off value of 500 ng/ml fibrinogen equivalent units (FEUs), D-dimer reagents differ in their abilities to avoid further testing. Indeed, LI allowed exclusion of VTE diagnosis in statistically more patients than VI, AX, and IN but not HS. The use of an age-adjusted cut-off is cost-effective without increasing significantly the number of false negative results. The interest of such strategy is more or less pronounced, depending on the type of D-dimer reagent. The application of an age-adjusted cut-off may be useful to reduce differences among D-dimer reagents to lower costly imaging studies. Prospective validation studies on large cohorts of patients are required to determine the safety of such strategy.

Comparison between different D-Dimer cutoff values to assess the individual risk of recurrent venous thromboembolism: analysis of results obtained in the DULCIS study

INTRODUCTION

D-dimer assay, generally evaluated according to cutoff points calibrated for VTE exclusion, is used to estimate the individual risk of recurrence after a first idiopathic event of venous thromboembolism (VTE).

METHODS

Commercial D-dimer assays, evaluated according to predetermined cutoff levels for each assay, specific for age (lower in subjects <70 years) and gender (lower in males), were used in the recent DULCIS study. The present analysis compared the results obtained in the DULCIS with those that might have been had using the following different cutoff criteria: traditional cutoff for VTE exclusion, higher levels in subjects aged ≥60 years, or age multiplied by 10.

RESULTS

In young subjects, the DULCIS low cutoff levels resulted in half the recurrent events that would have occurred using the other criteria. In elderly patients, the DULCIS results were similar to those calculated for the two age-adjusted criteria. The adoption of traditional VTE exclusion criteria would have led to positive results in the large majority of elderly subjects, without a significant reduction in the rate of recurrent event.

CONCLUSION

The results confirm the usefulness of the cutoff levels used in DULCIS.

[Usefulness of assessing hydration status in elderly patients over 70 years with suspected deep vein thrombosis]

INTRODUCTION

Venous thromboembolism and dehydration are frequent conditions in elderly. The objective of this study was to assess the prevalence of dehydration in patients aged over 70 years suspected of deep vein thrombosis (DVT).

METHODS

This is a prospective observational study that included patients aged over 70 years and suspected of deep vein thrombosis. Clinical and biological dehydration was diagnosed on the presence of a skin fold, a weight loss≥5%, a thirst, a plasmatic osmolality>295 mOsm/L or blood urea nitrogen/creatinine ratio>20.

RESULTS

One hundred and forty-four patients (mean age 81.8±5.8 years) were included. A diagnosis of DVT was retained in 97 patients. Clinical dehydration was not more frequent in the DVT+ group (37.2% vs 35.1%). At baseline, 69.1% of DVT+ patients and 53.2% of DVT- patients had a plasma osmolality greater than 295 mosm/L (NS). BUN/creatinine ratio greater than 20 was found in 58.8% of DVT+ patients and 72.3% of DVT- patients (NS). Clinical and biological dehydration was present in 28.6% of DVT+ patients and in 33.3% of DVT- patients (NS). The positive predictive value of the Wells score≥3 was 86.5%, and negative predictive value of a Wells score≤0 was 85%.

CONCLUSION

The presence of dehydration does not appear predictive of the occurrence of DVT and does not influence the statistical performance of the Wells score in elderly patients.

A higher d-dimer threshold safely rules-out pulmonary embolism in very elderly emergency department patients

INTRODUCTION

D-dimer is commonly used in the workup of suspected Pulmonary Embolism (PE), but its specificity decreases with age. We evaluated whether using a higher cutoff value for D-dimer could increase the test specificity without reducing its sensitivity for ruling-out PE in elderly and very elderly patients presenting to the Emergency Department (ED).

MATERIAL AND METHODS

All patients with D-dimer and pulmonary Computed Tomography Angiography (CTA) performed in the ED of Vimercate Hospital, from 2010 through 2012 for clinical suspicion of PE were included in this retrospective cohort study.

RESULTS

Study population 481 patients (63.4% women, mean age 73.0 ± 16.1 years, confirmed PE 22.5%). In very elderly patients (aged 80 or more years, n=191), compared with standard 490 ng/mL D-dimer threshold, both higher fixed (1000 ng/mL) and age-adjusted cutoffs increase the specificity of D-dimer for the exclusion of PE maintaining a Negative Predictive Value of 100%. Potentially avoided CTAs were 12(6.3%) using 1000 ng/mL cutoff and 10(5.2%) age-adjusted. In very elderly patients the Number Needed to Test was incalculable for the standard cutoff (0 cases), 16 for 1000 ng/mL and 19 for age-adjusted. In patients with PE, index episode mortality was 6.5%, and death occurred only in subjects with D-dimer values above 1000ng/mL and age-adjusted thresholds.

CONCLUSION

For very elderly patients with suspected PE in ED, both higher fixed D-dimer (1000 ng/mL) and age-adjusted thresholds increase test specificity for excluding PE without reducing its sensitivity, leading to a safe reduction in the number of CTAs.

Diagnostic accuracy of conventional or age adjusted D-dimer cut-off values in older patients with suspected venous thromboembolism: systematic review and meta-analysis

OBJECTIVE

To review the diagnostic accuracy of D-dimer testing in older patients (>50 years) with suspected venous thromboembolism, using conventional or age adjusted D-dimer cut-off values.

DESIGN

Systematic review and bivariate random effects meta-analysis.

DATA SOURCES

We searched Medline and Embase for studies published before 21 June 2012 and we contacted the authors of primary studies.

STUDY SELECTION

Primary studies that enrolled older patients with suspected venous thromboembolism in whom D-dimer testing, using both conventional (500 µg/L) and age adjusted (age × 10 µg/L) cut-off values, and reference testing were performed. For patients with a non-high clinical probability, 2 × 2 tables were reconstructed and stratified by age category and applied D-dimer cut-off level.

RESULTS

13 cohorts including 12,497 patients with a non-high clinical probability were included in the meta-analysis. The specificity of the conventional cut-off value decreased with increasing age, from 57.6% (95% confidence interval 51.4% to 63.6%) in patients aged 51-60 years to 39.4% (33.5% to 45.6%) in those aged 61-70, 24.5% (20.0% to 29.7% in those aged 71-80, and 14.7% (11.3% to 18.6%) in those aged >80. Age adjusted cut-off values revealed higher specificities over all age categories: 62.3% (56.2% to 68.0%), 49.5% (43.2% to 55.8%), 44.2% (38.0% to 50.5%), and 35.2% (29.4% to 41.5%), respectively. Sensitivities of the age adjusted cut-off remained above 97% in all age categories.

CONCLUSIONS

The application of age adjusted cut-off values for D-dimer tests substantially increases specificity without modifying sensitivity, thereby improving the clinical utility of D-dimer testing in patients aged 50 or more with a non-high clinical probability.

Validation of two age dependent D-dimer cut-off values for exclusion of deep vein thrombosis in suspected elderly patients in primary care: retrospective, cross sectional, diagnostic analysis

OBJECTIVE

To determine whether the use of age adapted D-dimer cut-off values can be translated to primary care patients who are suspected of deep vein thrombosis.

DESIGN

Retrospective, cross sectional diagnostic study.

SETTING

110 primary care doctors affiliated with three hospitals in the Netherlands.

PARTICIPANTS

1374 consecutive patients (936 (68.1%) aged >50 years) with clinically suspected deep vein thrombosis.

MAIN OUTCOME MEASURES

Proportion of patients with D-dimer values below two proposed age adapted cut-off levels (age in years × 10 μg/L in patients aged >50 years, or 750 μg/L in patients aged ≥ 60 years), in whom deep vein thrombosis could be excluded; and the number of false negative results.

RESULTS

Using the Wells score, 647 patients had an unlikely clinical probability of deep vein thrombosis. In these patients (at all ages), deep vein thrombosis could be excluded in 309 (47.8%) using the age dependent cut-off value compared with 272 (42.0%) using the conventional cut-off value of 500 μg/L (increase 5.7%, 95% confidence interval 4.1% to 7.8%). This exclusion rate resulted in 0.5% and 0.3% false negative cases, respectively (increase 0.2%, 0.004% to 8.6%).The increase in exclusion rate by using the age dependent cut-off value was highest in the oldest patients. In patients older than 80 years, deep vein thrombosis could be safely excluded in 22 (35.5%) patients using the age dependent cut-off value compared with 13 (21.0%) using the conventional cut-off value (increase 14.5%, 6.8% to 25.8%). Compared with the age dependent cut-off value, the cut-off value of 750 μg/L had a similar exclusion rate (307 (47.4%) patients) and false negative rate (0.3%).

CONCLUSIONS

Combined with a low clinical probability of deep vein thrombosis, use of the age dependent D-dimer cut-off value for patients older than 50 years or the cut-off value of 750 μg/L for patients aged 60 years and older resulted in a considerable increase in the proportion of patients in primary care in whom deep vein thrombosis could be safely excluded, compared with the conventional cut-off value of 500 μg/L.

Using an age-dependent D-dimer cut-off value increases the number of older patients in whom deep vein thrombosis can be safely excluded

BACKGROUND

D-dimer testing to rule out deep vein thrombosis is less useful in older patients because of a lower specificity. An age-adjusted D-dimer cut-off value increased the proportion of older patients (>50 years) in whom pulmonary embolism could be excluded. We retrospectively validated the efficacy of this cut-off combined with clinical probability for the exclusion of deep vein thrombosis.

DESIGN AND METHODS

Five management study cohorts of 2818 consecutive outpatients with suspected deep vein thrombosis were used. Patients with non-high or unlikely probability of deep vein thrombosis were included in the analysis; four different D-dimer tests were used. The proportion of patients with a normal D-dimer test and the failure rates were calculated using the conventional (500 μg/L) and the age-adjusted D-dimer cut-off (patient's age x 10 μg/L in patients >50 years).

RESULTS

In 1672 patients with non-high probability, deep vein thrombosis could be excluded in 850 (51%) patients with the age-adjusted cut-off value versus 707 (42%) patients with the conventional cut-off value. The failure rates were 7 (0.8; 95% confidence interval 0.3-1.7%) for the age-adjusted cut-off value and 5 (0.7%, 0.2-1.6%) for the conventional cut-off value. The absolute increase in patients in whom deep vein thrombosis could be ruled out using the age-adjusted cut-off value was largest in patients >70 years: 19% among patients with non-high probability.

CONCLUSIONS

The age-adjusted cut-off of the D-dimer combined with clinical probability greatly increases the proportion of older patients in whom deep vein thrombosis can be safely excluded.

Inappropriate use of D-dimer assay and pulmonary CT angiography in the evaluation of suspected acute pulmonary embolism

The authors question whether the d-dimer assay and pulmonary computed tomography angiography (CTA) are being used appropriately to evaluate suspected acute pulmonary embolism (PE) at their hospital. To answer this question, a retrospective review was performed on all emergency department (ED) patients who underwent d-dimer assay and/or CTA from August 15, 2008, to August 14, 2009. The authors' algorithm for diagnosing PE requires that patients with low or intermediate probability of acute PE undergo a d-dimer assay, followed by CTA if the d-dimer is positive. Patients with high probability of PE should have CTA performed without a d-dimer assay. This result suggests that d-dimer assay and CTA are used inappropriately to evaluate patients with suspected acute PE in our ED. The low threshold for initiating an evaluation for PE decreases the prevalence of PE in this population.