Rapid fibrin D-dimer tests for deep venous thrombosis: factors affecting diagnostic utility

Correlation Between D-Dimer Concentrations and Thromboelastography in Dogs With Critical Illness: A Retrospective, Cross-Sectional Study

A hospital-based, retrospective, cross-sectional study was performed to assess the correlation of kaolin-activated thromboelastography (TEG) with D-dimer concentrations in 59 dogs with critical illness. Dogs were included if they had one or more serious disease detected upon performing TEG and D-dimer concentration determination based on the same blood sample. According to the coagulation index (CI), the 59 dogs were divided into two groups: a hypercoagulable state, with CI > 4 (44 dogs) and a normocoagulable state, with CI < 4 (15 dogs). Moreover, the 44 dogs with CI > 4 were divided into three sub-groups according to the disease etiology, i.e., inflammatory/tumor (I/T: 25 dogs), hemodynamic compromise (H: 11 dogs), and both conditions (I/TH: 8 dogs). The median values (interquartile ranges) of the CI and D-dimer concentration were 5.46 (4.55–6.33) and 410.25 (74.63–2206.12) in the 44 dogs with CI > 4 and 3.29 (2.92–3.75) and 1164.7 (50–2250.05) in the 15 dogs with CI < 4, respectively. The D-dimer concentration was significantly increased over the reference value in the 44 dogs with a CI > 4, particularly in dogs in the I/T group. It was also significantly increased in the 15 dogs with a CI < 4. D-dimer concentrations did not correlate with any of the TEG parameters in any of the dogs. Given this lack of correlation, the D-dimer concentration may be limited as an indicator of a possible hypercoagulable state in dogs with critical illness.

Variation in the diagnostic performance of D-dimer for suspected deep vein thrombosis

BACKGROUND

Numerous studies have evaluated the accuracy of D-dimer in diagnosing suspected deep vein thrombosis (DVT), but results are conflicting.

AIM

To overview estimates of the diagnostic accuracy of D-dimer and identify causes of variation.

DESIGN

Systematic review, meta-analysis and meta-regression.

METHODS

We searched Medline, EMBASE, CINAHL, Web of Science, Cochrane Database of Systematic Reviews, Cochrane Controlled Trials Register, Database of Reviews of Effectiveness, the ACP Journal Club, citation lists, and contacted manufacturers. We selected studies that compared D-dimer to a reference standard in patients with suspected DVT. Data were analysed by random effects meta-analysis and meta-regression.

RESULTS

We included 97 studies reporting 198 assays in 99 different patient groups. Overall estimated sensitivity and specificity of D-dimer were 90.5% and 54.7%, but both estimates were subject to significant heterogeneity (p < 0.001). Meta-regression identified that some heterogeneity was explained by study setting, exclusion criteria, whether recruitment was consecutive or the study prospective, whether D-dimer and the reference standard were measured blind, and whether the D-dimer threshold was determined a priori. Sensitivity and specificity also varied between ELISA (94% and 45% respectively), latex (89% and 55%) and whole blood agglutination assays (87% and 68%). Sensitivity was higher for proximal than distal DVT. Specificity was dependent upon whether clinical probability of DVT was high (specificity 51%), intermediate (67%) or low (78%).

DISCUSSION

D-dimer has good sensitivity, but poor specificity, for DVT. Estimates are subject to substantial heterogeneity from various sources. D-dimer specificity appears to be strongly dependent upon the pre-test clinical probability of DVT.

D-dimer testing for deep venous thrombosis: a metaanalysis

BACKGROUND

The use of D-dimer assays as a rule-out test for deep venous thrombosis (DVT) is controversial. To clarify this issue we performed a systematic review of the relevant literature.

METHODS

We identified eligible studies, using MEDLINE entries from February 1995 through October 2003, supplemented by a review of bibliographies of relevant articles. Studies reporting accuracy evaluations comparing D-dimer test results with lower extremity ultrasound or venography in symptomatic patients with suspected acute DVT were selected for review. Two reviewers critically appraised each study independently according to previously established methodologic standards for diagnostic test research. Those studies judged to be of highest quality were designated Level 1.

RESULTS

The 23 Level 1 studies reported data on 21 different D-dimer assays. There was wide variation in assay sensitivity, specificity, and negative predictive values, and major differences in methodology of reviewed studies. A multivariate analysis of assay performance, controlling for sample size, DVT prevalence, reference standard, and patient mix, found few differences among the assays in effect on test performance as measured by diagnostic odds ratio. Increasing prevalence of DVT was associated with poorer test performance (P = 0.01), whereas the choice of venography as the reference standard was associated with better test performance (P <0.005).

CONCLUSIONS

Explanations for the wide variation in assay performance include differences in biochemical and technical characteristics of the assays, heterogeneity and small size of patient groups, and bias introduced by choice of reference standards. Assay sensitivity and negative predictive value were frequently <90%, uncharacteristic of a good rule-out test. General use of D-dimer assays as a stand-alone test for the diagnosis of DVT is not supported by the literature.

Diagnosing pulmonary embolism: a question of too much choice?

The diagnosis of pulmonary embolism (PE) is difficult with many patients treated without the disease or left untreated without an adequate diagnostic work up. Recent advances in PE diagnosis are reviewed. The use of risk stratification in PE diagnosis is strongly recommended and evidence on how it can best be performed summarized. The Ginsberg/Wells stratification rule is recommended currently as the best validated rule. Computed tomographic pulmonary angiography (CTPA) was found to have quite poor sensitivity and to be poorly validated. It is recommended as adequate as a positive test in moderate/high risk groups and an exclusionary test in low risk groups or where an adequate alternative diagnosis is found. For D-Dimer tests the only test with adequate sensitivity and validation in management studies is the VIDASCopyright D-Dimer. This is in low/intermediate risk groups in the ED population. The Simpli-RedCopyright test is also reviewed but is too insensitive for most populations. Echocardiography: this is good in compromised patients as it is a bedside test which when negative virtually excludes PE. If positive in the right setting it has a high positive predictive value. A negative echocardiogram predicts a benign clinical course for PE. The rest of the paper details the authors approach to integrating these new techniques with established algorithms and where progress is likely to occur in the next few years. These include improvements in CTPA (plus the addition of CT venography), new point of care D-Dimer tests, better risk stratification rules and integration of new strategies with artificial neural networks or computerized guidelines.

Nonspecific tests for pulmonary embolism

Many tests have been proposed as useful in the diagnostic evaluation of suspected PE, but nonspecific tests for PE can only add to the level of suspicion one has for the diagnosis. As Anderson indicates, "virtually all clinical and laboratory findings neither diagnose nor exclude the diagnosis of PE. They merely serve to heighten suspicion of the diagnosis and prompt the clinician to pursue additional diagnostic studies." D-dimer measurement is promising as a test to exclude PE in young healthy out-patients, and further study and improvements in technology, can clarify the usefulness of the different methods of performing this assay. For now, diagnostic algorithms for PE should continue to incorporate multiple tests and decision points, but the standard remains specialized imaging techniques.

Management of patients with suspected deep vein thrombosis in the emergency department: combining use of a clinical diagnosis model with D-dimer testing

The management of patients presenting to hospital Emergency Departments with suspected deep vein thrombosis is problematic since urgent diagnostic imaging is at times unavailable. We evaluated the accuracy of a rapidly available D-dimer test and the potential of combining D-dimer testing with an explicit clinical model to improve the management of patients with suspected deep vein thrombosis. Two hundred and fourteen patients with suspected deep vein thrombosis presenting to the Emergency Departments of two tertiary care institutions were enrolled in this prospective cohort study. Patients were evaluated by an Emergency Physician who determined the pre-test probability for deep vein thrombosis to be either low, moderate, or high using an explicit clinical model. Patients were managed according to their pre-test probability category by specific algorithms that in all cases included venous ultrasound imaging within 24 h and a 90-day follow-up for the development of thromboembolic complications. Patients also underwent fingerstick SimpliRED(R) whole blood agglutination D-dimer testing; however, D-dimer results did not influence subsequent patient management. D-dimer had a sensitivity of 82.5% and a specificity of 84.9% for the diagnosis of deep vein thrombosis. The observed negative predictive value of D-dimer was 96.9% (95% CI, 93.0% to 99.1%) overall, and 100% (95% CI, 96.3% to 100%) in low probability patients, 94.1% (95% CI, 83.8% to 98.8%) in moderate probability patients, and 86.7% (95% CI, 59.4% to 98.3%) in high probability patients. SimpliRED(R) D-dimer has a high negative predictive value and may be useful in excluding the diagnosis in patients at low pre-test probability for deep vein thrombosis.

D-dimer for the diagnosis of venous thromboembolism

D-dimer, a breakdown product of cross-linked fibrin has been extensively evaluated as a diagnostic test for acute venous thromboembolism. Rapid, highly sensitive D-dimer assays are now available that are suitable for testing in the emergency setting. Preliminary studies suggest that when using a highly sensitive D-dimer assay, a negative test result may,be sufficient to exclude the diagnosis of venous thromboembolism without need for further testing. Less sensitive, but more specific D-dimer assays are also available. The negative predictive value of these latter assays is insufficient to exclude venous thromboembolism on the basis of a negative test result alone. However, their utility is increased by identifying patient populations at low risk for venous thromboembolism using consideration of clinical probability or radiographic testing. Further, large multicenter management studies are required to confirm the safety of relying on a negative D-dimer result to exclude the diagnosis of venous thromboembolism.