Diagnostic accuracy of the Triage® D-dimer test for exclusion of venous thromboembolism in outpatients

Unified calibration of D-dimer can improve the uniformity of different detection systems

Background

D-dimer at a low level is important evidence for excluding the onset and progression of thrombosis. It is readily detectable and yields rapid results, although significant variability exists among different detection systems. Our study aims to enhance the consistency across various detection systems.

Methods

Twelve detection systems were included in our study. We sought to address this inconsistency by using various calibrators (two supplied by manufacturers and two comprising pooled human plasma diluted with different diluents) to standardize D-dimer measurements. We categorized the data into three groups according to D-dimer concentration levels: low (≤0.5 mg/L), medium (>0.5 mg/L - <3 mg/L), and high (≥3 mg/L). We then analyzed the data focusing on range, consistency, comparability, negative coincidence rate, and false negative rate.

Results

Calibrating with pooled human plasma led to narrower result ranges in the low and medium groups (P < 0.05). In the low group, consistency improved from weak to strong (ICC 0.4-0.7, P﹤0.05), while it remained excellent in the other groups and overall (ICC﹥0.75, P﹤0.05). The percentage of pairwise comparability increased in both the low and high groups. Additionally, there was an increase in the negative coincidence rate.

Conclusion

These findings demonstrate that uniform calibration of D-dimer can significantly enhance the consistency of results across different detection systems.

Two point-of-care test-based approaches for the exclusion of deep vein thrombosis in general practice: a cost-effectiveness analysis

BACKGROUND

In the diagnostic work-up of deep vein thrombosis (DVT), the use of point-of-care-test (POCT) D-dimer assays is emerging as a promising patient-friendly alternative to regular D-dimer assays, but their cost-effectiveness is unknown. We compared the cost-effectiveness of two POCT-based approaches to the most common, laboratory-based, situation.

METHODS

A patient-level simulation model was developed to simulate the diagnostic trajectory of patients presenting with symptoms of DVT at the general practitioner (GP). Three strategies were defined for further diagnostic work-up: one based on current guidelines ('regular strategy') and two alternative approaches where a POCT for D-dimer is implemented at the 1) phlebotomy service ('DVT care pathway') and 2) GP practice ('fast-POCT strategy'). Probabilities, costs and health outcomes were obtained from the literature. Costs and effects were determined from a societal perspective over a time horizon of 6 months. Uncertainty in model outcomes was assessed with a one-way sensitivity analysis.

RESULTS

The Quality-Adjusted Life Years (QALYs) scores for the three DVT diagnostic work-up strategies were all around 0.43 across a 6 month-time horizon. Cost-savings of the two POCT-based strategies compared to the regular strategy were €103/patient for the DVT care pathway (95% CI: -€117-89), and €87/patient for the fast-POCT strategy (95% CI: -€113-67).

CONCLUSIONS

Point-of-care-based approaches result in similar health outcomes compared with regular strategy. Given their expected cost-savings and patient-friendly nature, we recommend implementing a D-dimer POCT device in the diagnostic DVT work-up.

Evaluation of three commercial kits effective identification of menstrual blood based on the D-dimer

Blood or bloodstains are encountered frequently in forensic investigations. Presumptive and more confirmatory tests for peripheral blood are well established, however, similar methods for menstrual blood identification are less so. D-dimer is a fibrin degradation product that occurs at high concentration in menstrual blood and therefore a potential target to screen for this body fluid. We evaluated three rapid tests to determine if they can discriminate menstrual blood from peripheral remote from a laboratory setting. Their sensitivity, specificity and robustness were also assessed. The assays were: a latex agglutination (Dade Dimertest Latex Assay), SERATEC PMB test and OneStep D-dimer RapidCard InstaTest, both of which are based on lateral flow immunochromatographic analysis. Of the three, greater sensitivity was observed using the OneStep D-dimer RapidCard InstaTest, regardless of whether liquid or a stain was used. This test also detected a result using the smallest volume of menstrual blood, 0.003125 μL. Specificity testing was based on six different body fluids (urine, saliva, peripheral blood, semen, sweats and vaginal fluid) resulting in all 30 samples testing negative for the D-dimer using the OneStep D-dimer RapidCard InstaTest. Mixtures at ratios 1:1, 1:3 and 1:9 (menstrual blood: the other biofluid or PBS) were tested and the results showed that D-dimer could be detected for all samples using either the Dade Dimertest Latex Assay or the OneStep D-dimer RapidCard InstaTest. The body fluids were exposed to environmental stresses such as various temperature (-20 °C, 4 °C, room temperature and 37 °C for 30, 90, 180 and 360 days) and fluctuations in humidity (42%, 76% and 100% humidity at room temperature for 1, 3, 5, 10 and 20 days): all samples were D-dimer positive using the OneStep D-dimer RapidCard InstaTest though the strength decreased relative to the increase of storage time and temperature or humidity. All 6 postmortem blood samples gave a positive result for D-dimer using the OneStep D-dimer RapidCard InstaTest and 2 samples gave a positive response using the Dade Dimertest Latex Assay and the SERATEC PMB test; peripheral blood postmortem samples can show an increase in D-dimer. Menstrual blood was recovered from the pads under the sample wells after testing using the two immunochromatographic assays from which STR alleles could be amplified successfully. The results presented here support the application of these commercial kits for effective identification of menstrual blood.

The D-dimer assay

D-dimer is an indirect marker of fibrinolysis and fibrin turnover; this molecule exhibits unique properties as a biological marker of hemostatic abnormalities as well as an indicator of intravascular thrombosis. D-dimer is a soluble fibrin degradation product that results from the systematic degradation of vascular thrombi through the fibrinolytic mechanism. Because of this, the D-dimer serves as a valuable marker of activation of coagulation and fibrinolysis in a number of clinical scenarios. Most commonly, D-dimer has been extensively investigated for excluding the diagnosis of venous thromboembolism (VTE) and is used routinely for this indication. In addition, D-dimer has been evaluated for determining the optimal duration of anticoagulation in VTE patients, for diagnosing and monitoring disseminated intravascular coagulation, and for monitoring other conditions in which the patient is at high risk of bleeding or thrombosis. Limitations of the assay include D-dimer elevation in a constellation of clinical scenarios (age, pregnancy, and cancer) and lack of clinical standardization.

Widely Used Types and Clinical Applications of D-Dimer Assay

D-dimers are formed by the breakdown of fibrinogen and fibrin during fibrinolysis. D-dimer analysis is critical for the diagnosis of deep vein thrombosis, pulmonary embolism, and disseminated intravascular coagulation. Modern assays for D-dimer are monoclonal antibody based. The enzyme-linked immunosorbent assay (ELISA) is the reference method for D-dimer analysis in the central clinical laboratory, but is time consuming to perform. Recently, a number of rapid, point-of-care D-dimer assays have been developed for acute care settings that utilize a variety of methodologies. In view of the diversity of D-dimer assays used in central laboratory and point-of-care settings, several caveats must be taken to assure the proper interpretation and clinical application of the results. These include consideration of preanalytical variables and interfering substances, as well as patient drug therapy and underlying disease. D-dimer assays should also be validated in clinical studies, have established cut-off values, and reported according to the reagent manufacturers recommendations.

Fluorescence immunoassay of human D-dimer in whole blood

BACKGROUND

D-dimer is a widely used biomarker for the initial clinical assessment of suspected deep vein thrombosis and pulmonary embolism. Here, we presented a new fluorescence (FL) D-dimer assay system, which was developed with a platform of point-of-care test (POCT) for clinical applications.

METHODS

Whole blood was mixed with FL-labeled anti-D-dimer detector antibody, and then loaded onto a disposable cartridge. After 12 min of incubation, the FL intensity was acquired by scanning of test cartridge and converted as level of D-dimer in a laser FL scanner. The analytical performance of FL immunoassay was evaluated by linearity, recovery, and precision tests. The comparability of the developed assay was examined with automated reference methods.

RESULTS

The FL assay system showed a good linearity, and the analytical mean recovery of control was 103% in a dynamic working range. The imprecision of intra- and inter-as-say of coefficient of variations from assay system was less than 8%. The developed FL assay system showed strong correlation with two automated reference assays, Vidas D-dimer (r = 0.973) and Stalia D-dimer (r = 0.971).

CONCLUSION

The new FL immunoassay for D-dimer is a user-friendly, precise, and reproducible platform of POCT in whole blood.

Clinical and biochemical diagnosis of small-vessel disease in acute ischemic stroke

BACKGROUND AND PURPOSE

Both from clinical and research standpoints, it may be highly relevant to differentiate between small-artery and large-artery infarction in the acute phase of ischemic stroke. We conducted a study on the added value of two D-dimer assays over clinical assessment for diagnosis of lacunar infarction.

METHODS

Clinical evaluation using the Oxfordshire Community Stroke Project (OCSP) classification and measurement of plasma D-dimer levels by the VIDAS D-dimer test (VIDAS) and the Triage Stroke Panel (TSP) were performed in 128 patients with ischemic stroke presenting within 9 h after onset of symptoms. The stroke subtype was defined as small-artery or large-artery infarction based on the TOAST classification.

RESULTS

The overall accuracy for diagnosing of acute lacunar stroke using the OCSP classification, VIDAS (cut point for D-dimer 445 ng/mL) or TSP (cut point 300 ng/mL) was 89%, 88% and 87% respectively (P<0.001). The conjunctive use of the OCSP classification and VIDAS or TSP improved the accuracy to 97% and 98% respectively (P<0.001). The kappa coefficient for agreement between the two assays was acceptable (kappa, 0.64). These results were reproducible in subgroups of patients presenting within 4.5 h and within 6 h after onset of stroke symptoms.

CONCLUSIONS

Diagnosis of acute lacunar infarction can reliably be made, based on the conjunctive use of clinical evaluation and measurement of D-dimer levels either by a standard assay or by a bedside testing kit.