Variable D-dimer thresholds for diagnosis of clinically suspected acute pulmonary embolism

Low Risk Meets High Stakes: Unraveling the Mystery of Low D-dimer Pulmonary Embolism

Pulmonary embolisms (PEs) are potentially life-threatening emergencies that carry significant morbidity and mortality. Advances in treatment options and the safety of existing procedures have effectively reduced the long-term and short-term effects of the condition. Therefore, it is important to make an early diagnosis so that treatment options can be thoroughly explored. The D-dimer is an important tool in the early diagnosis of PEs. It is especially useful in ruling out the diagnosis in patients with a low to moderate suspicion of the disease. We present a case of a 22-year-old male who presented with exertional dyspnea, congestion, and rhinorrhea for one day and was noted to have persistent hypoxia and tachycardia. The influenza test was positive, and he was started on oseltamivir. Due to persistent hypoxia, a CT pulmonary angiogram was ordered and revealed filling defects in the left lower lobe segmental vessels suggestive of PE, as well as multifocal multilobar bilateral ground-glass opacities. He was initially treated with a heparin drip and subsequently switched to eliquis. After a significant improvement in his hypoxia, he was discharged home for outpatient follow-up, including a hypercoagulable workup. This case demonstrates that despite the usefulness of the D-dimer as a diagnostic tool for PEs, it cannot solely or fully replace the full gamut of screening tools used to determine the risk of PE. Although rare, false-negative scores do occur; therefore, the tool should always be used in conjunction with other scoring systems, physician gestalt, and within the specific clinical context.

D-dimer and outcomes in hospitalized heart failure patients across the ejection fraction phenotypes

AIMS

The prognostic significance of D-dimer in hospitalized heart failure (HF) patients is incompletely characterized. We aimed to assess the association of D-dimer levels on admission with adverse events at follow-up in patients hospitalized with HF across all ejection fraction (EF) phenotypes.

METHODS AND RESULTS

Consecutive patients hospitalized from December 2006 to December 2017 for HF with D-dimer and EF values available (n = 1795) were enrolled. Associations between D-dimer and all-cause death were examined at 1-year follow-up. Median age was 57 years, 73.4% were male, and the majority (72.1%) were in New York Heart Association Classes III-IV. EF was reduced in 53.3% (HFrEF), mildly reduced in 16.3% (HFmrEF), and preserved in 30.4% (HFpEF). Median (interquartile range) D-dimer on admission was 0.56 (0.27-1.295) μg/mL FEU (fibrinogen-equivalent unit) in the whole cohort, 0.64 (0.28-1.48) μg/mL FEU in HFrEF, 0.50 (0.27-1.03) μg/mL FEU in HFmrEF, and 0.495 (0.25-1.10) μg/mL FEU in HFpEF (P = 0.001). At 1-year follow-up, higher D-dimer (D-dimer ≥0.56 μg/mL FEU) independently predicted all-cause death in total cohort [hazard ratio (HR) 1.55; 95% confidence interval (CI), 1.15-2.1], in HFrEF (HR, 1.49; P = 0.039), and in HFpEF (HR, 2.06; P = 0.033). However, no relationship was found for HFrEF or HFmrEF when D-dimer was treated as quartiles. In sensitivity analysis, quantitatively similar but more pronounced association between D-dimer and all-cause death was observed in total cohort and HFpEF cohort.

CONCLUSIONS

In hospitalized HF patients, higher D-dimer concentration was a significant and independent predictor of 1-year all-cause mortality. Across all HF phenotypes, this effect was most evident in HFpEF patients.

Effects of long-term high-altitude exposure on fibrinolytic system

OBJECTIVE

High altitude (HA), with the main feature of hypobaric hypoxia, is an independent risk factor for thrombosis. However, little is known on the alterations of fibrinolytic system in adaptation to HA. In this study, we investigated changes of fibrinolytic system parameters between individuals permanently living at HA and low altitude (LA) regions, and provided data for further studies on HA-induced thrombotic disease.

MATERIAL AND METHODS

A total of 226 eligible participants, including 103 LA participants, 100 healthy HA subjects and 23 high altitude polycythemia (HAPC) patients, were recruited in this study. Six fibrinolytic parameters, i.e. fibrinogen (Fbg), D-dimer (DDi), antithrombin III (AT-III), plasminogen activator inhibitor-1 (PAI-1), tissue plasminogen activator (tPA) and plasminogen (PLG) were analyzed respectively. PAI-1 and tPA were performed by using bio-immuno-assays and an automated coagulation analyzer was used to conduct Fbg, DDi, AT-III and PLG tests.

RESULTS

Plasma levels of Fbg, DDi, PAI-1 and PLG were significantly higher in healthy HA group than in LA group (all p < 0.05), whereas tPA was significantly lower in healthy HA group. No significant difference in AT-III was observed between healthy HA and LA groups (p > 0.05). All these fibrinolytic parameters showed no significant distinctions between healthy HA subjects and HAPC patients (all p > 0.05). HGB showed no relationship with fibrinolytic parameters in HA cohort.

CONCLUSION

This study demonstrates that HA environment has a significant effect on fibrinolytic system and provides a foundation for further studies on HA hypobaric hypoxia-induced thrombotic disease.

Current Challenges in Diagnosis of Venous Thromboembolism

In patients with suspected venous thromboembolism, the goal is to accurately and rapidly identify those with and without thrombosis. Failure to diagnose venous thromboembolism (VTE) can lead to fatal pulmonary embolism (PE), and unnecessary anticoagulation can cause avoidable bleeding. The adoption of a structured approach to VTE diagnosis, that includes clinical prediction rules, D-dimer testing and non-invasive imaging modalities, has enabled rapid, cost-effective and accurate VTE diagnosis, but problems still persist. First, with increased reliance on imaging and widespread use of sensitive multidetector computed tomography (CT) scanners, there is a potential for overdiagnosis of VTE. Second, the optimal strategy for diagnosing recurrent leg deep venous thrombosis remains unclear as is that for venous thrombosis at unusual sites. Third, the conventional diagnostic approach is inefficient in that it is unable to exclude VTE in high-risk patients. In this review, we outline pragmatic approaches for the clinician faced with difficult VTE diagnostic cases. In addition to discussing the principles of the current diagnostic framework, we explore the diagnostic approach to recurrent VTE, isolated distal deep-vein thrombosis (DVT), pregnancy associated VTE, subsegmental PE, and VTE diagnosis in complex medical patients (including those with impaired renal function).

Bone Microthrombus Promotes Bone Loss in Iron Accumulation Rats

In the present study, we investigated the changes of the coagulation state, bone microthrombus, microvascular bed and bone density levels in iron accumulation rats. Meanwhile,the effect of anticoagulation therapy on bone mineral density was further investigated. We established two groups: a control (Ctrl) group and an iron intervention (FAC) group. Changes in coagulation function, peripheral blood cell counts, bone microthrombus, bone vessels and bone mineral density were compared between the two groups. We designed the non-treatment group and treatment group to study the changes of bone mineral density by preventing microthrombus formation with the anticoagulant fondaparinux. We found that the fibrinogen and D-dimer contents were significantly higher, whereas the thrombin time (TT) and prothrombin time (PT) were significantly shorter in the FAC group. After ink staining, the microvascular bed in the FAC group was significantly reduced compared with that in the Ctrl group. HE and Martius Scarlet Blue (MSB) staining showed microthrombus in the bone marrow of the iron accumulation rats. Following anticoagulation therapy, the bone microcirculation vascular bed areas in the treatment group rats were significantly increased. Furthermore, the bone mineral density was increased in the treatment group compared with that in the non-treatment group. Through experiments, we found that the blood in iron accumulation rat was relatively hypercoagulable; moreover, there was microthrombus in the bone marrow, and the bone vascular bed was reduced. Additionally, anticoagulation was helpful for improving bone microcirculation, reducing microthrombus and decreasing bone loss.

Association Between D-dimer and Early Adverse Events in Patients With Acute Type A Aortic Dissection Undergoing Arch Replacement and the Frozen Elephant Trunk Implantation: A Retrospective Cohort Study

Objective

In the present study, we investigated the associations between D-dimer levels at admission and early adverse events in patients with acute type A aortic dissection undergoing arch replacement and the frozen elephant trunk (FET).

Methods

We retrospectively analyzed data of patients with acute type A aortic dissection undergoing aortic arch surgery and FET from July 2017 to December 2018 at Beijing Anzhen Hospital. D-dimer levels were evaluated within 24 h of admission. Multivariate Cox regression analysis was used to determine independent predictors of early postoperative adverse events.

Results

A total of 347 patients were included in the study. The average age of the patients was 48.07 ± 10.56 years, with male predominance (79.25%). The incidence of 90-day postoperative adverse events was 18.7%, consisting of 14.7% mortality and 4.0% permanent neurological dysfunction (PND). The median D-dimer level was 1.95 ug/ml (interquartile range, 0.77–3.16 ug/ml). Multivariable Cox regression analysis revealed that D-dimer level was independently associated with 90-day postoperative adverse events after adjustment for confounding factors (hazard ratio = 1.19 per 10 ug/ml increase in D-dimer, 95% confidence interval: 1.01–1.41; P = 0.039). Kaplan–Meier analysis revealed that the highest tertile (median 6.27 ug/ml) had more 90-day postoperative adverse events compared with the median and lowest tertiles (P = 0.0014). Sub-analysis found that the association remained unchanged.

Conclusion

Increased D-dimer levels at admission were associated with 90-day postoperative adverse events in patients with acute type A aortic dissection undergoing arch replacement and FET. These results may help clinicians optimize the risk evaluation and perioperative clinical management to reduce early adverse events.

Key Question

Explore the relationship between D-dimer and early outcomes in patients with aortic dissection with arch replacement.

Key Findings

Increased D-dimer at admission was associated with adverse events in patients with aortic dissection with arch surgery.

Take-Home Message

The high-risk patients deserve close medical monitoring.

Diagnosis of Pulmonary Embolism with d-Dimer Adjusted to Clinical Probability

BACKGROUND

Retrospective analyses suggest that pulmonary embolism is ruled out by a d-dimer level of less than 1000 ng per milliliter in patients with a low clinical pretest probability (C-PTP) and by a d-dimer level of less than 500 ng per milliliter in patients with a moderate C-PTP.

METHODS

We performed a prospective study in which pulmonary embolism was considered to be ruled out without further testing in outpatients with a low C-PTP and a d-dimer level of less than 1000 ng per milliliter or with a moderate C-PTP and a d-dimer level of less than 500 ng per milliliter. All other patients underwent chest imaging (usually computed tomographic pulmonary angiography). If pulmonary embolism was not diagnosed, patients did not receive anticoagulant therapy. All patients were followed for 3 months to detect venous thromboembolism.

RESULTS

A total of 2017 patients were enrolled and evaluated, of whom 7.4% had pulmonary embolism on initial diagnostic testing. Of the 1325 patients who had a low C-PTP (1285 patients) or moderate C-PTP (40 patients) and a negative d-dimer test (i.e., <1000 or <500 ng per milliliter, respectively), none had venous thromboembolism during follow-up (95% confidence interval [CI], 0.00 to 0.29%). These included 315 patients who had a low C-PTP and a d-dimer level of 500 to 999 ng per milliliter (95% CI, 0.00 to 1.20%). Of all 1863 patients who did not receive a diagnosis of pulmonary embolism initially and did not receive anticoagulant therapy, 1 patient (0.05%; 95% CI, 0.01 to 0.30) had venous thromboembolism. Our diagnostic strategy resulted in the use of chest imaging in 34.3% of patients, whereas a strategy in which pulmonary embolism is considered to be ruled out with a low C-PTP and a d-dimer level of less than 500 ng per milliliter would result in the use of chest imaging in 51.9% (difference, -17.6 percentage points; 95% CI, -19.2 to -15.9).

CONCLUSIONS

A combination of a low C-PTP and a d-dimer level of less than 1000 ng per milliliter identified a group of patients at low risk for pulmonary embolism during follow-up. (Funded by the Canadian Institutes of Health Research and others; PEGeD ClinicalTrials.gov number, NCT02483442.).

A Test in Context: D-Dimer

D-dimer is a soluble fibrin degradation product that results from ordered breakdown of thrombi by the fibrinolytic system. Numerous studies have shown that D-dimer serves as a valuable marker of activation of coagulation and fibrinolysis. Consequently, D-dimer has been extensively investigated for 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 as an aid in the identification of medical patients at high risk for VTE. Thus, quantification of D-dimer levels serves an important role in guiding therapy. This review: 1) describes how D-dimer is generated; 2) reviews the assays used for its detection; and 3) discusses the role of D-dimer determination in these various conditions.

D-dimer Interval Likelihood Ratios for Pulmonary Embolism

OBJECTIVE

The objective was to estimate D-dimer interval likelihood ratios (iLRs) for diagnosing pulmonary embolism (PE).

METHODS

The authors used pooled patient-level data from five PE diagnostic management studies to estimate iLRs for the eight D-dimer intervals with boundaries 250, 500, 750, 1,000, 1,500, 2,500, and 5,000 ng/mL. Logistic regression was used to fit the data so that an interval increase corresponds to increasing the likelihood ratio by a constant factor.

RESULTS

The iLR for the D-dimer interval 1,000-1,499 ng/mL was essentially 1.0 (0.98 with 95% confidence interval [CI] = 0.82-1.18). In the logistic regression model, the constant between-interval factor was 2.0 (95% CI = 1.9-2.1). Using these iLR estimates, if the pre-D-dimer probability of PE is 15%, only a D-dimer less than 500 ng/mL will result in a posttest probability below 3%; if the pretest probability is 5%, the threshold for a "negative" D-dimer is 1,000 ng/mL.

CONCLUSIONS

A decision strategy based on these approximate iLRs agrees with several published strategies.

Diagnosis of suspected venous thromboembolism

The primary goal of diagnostic testing for venous thromboembolism (VTE) is to identify all patients who could benefit from anticoagulant therapy. Test results that identify patients as having a ≤2% risk of VTE in the next 3 months are judged to exclude deep vein thrombosis (DVT) or pulmonary embolism (PE). Clinical evaluation, with assessment of: (1) clinical pretest probability (CPTP) for VTE; (2) likelihood of important alternative diagnoses; and (3) the probable yield of D-dimer and various imaging tests, guide which tests should be performed. The combination of nonhigh CPTP and negative D-dimer testing excludes DVT or PE in one-third to a half of outpatients. Venous ultrasound of the proximal veins, with or without examination of the distal veins, is the primary imaging test for leg and upper-extremity DVT. If a previous test is not available for comparison, the positive predictive value of ultrasound is low in patients with previous DVT. Computed tomography pulmonary angiography (CTPA) is the primary imaging test for PE and often yields an alternative diagnosis when there is no PE. Ventilation-perfusion scanning is associated with less radiation exposure than CTPA and is preferred in younger patients, particularly during pregnancy. If DVT or PE cannot be "ruled-in" or "ruled-out" by initial diagnostic testing, patients can usually be managed safely by: (1) withholding anticoagulant therapy; and (2) doing serial ultrasound examinations to detect new or extending DVT.

Recent developments in the diagnosis and treatment of pulmonary embolism

Due to the nonspecific symptoms of the condition, a diagnosis of acute pulmonary embolism (PE) is frequently considered. However, PE will only be confirmed in 10-20% of patients. Because the imaging test of choice, computed tomography pulmonary angiography (CTPA), is costly and associated with radiation exposure and other complications, a validated diagnostic algorithm consisting of a clinical decision rule and D-dimer test should be used to safely exclude PE in 20-30% of patients without the need for CTPA. Recently, the age-adjusted D-dimer threshold has been validated, and this has increased the proportion of patients at older age in whom PE can be excluded without CTPA. Initial therapeutic management of PE depends on the risk of short-term PE-related mortality. Haemodynamically unstable patients should be closely monitored and receive thrombolytic therapy unless contraindicated because of an unacceptably high bleeding risk, whereas patients with low-risk PE may be safely discharged early from hospital or receive only outpatient treatment. The PESI score and Hestia decision rule are available to select patients in whom early discharge or outpatient treatment will be safe, although the safety of these strategies should be confirmed in additional studies. Standard PE therapy consists of low molecular weight heparin (LMWH) followed by vitamin K antagonists (VKAs). Recently, several nonvitamin K-dependent oral anticoagulants have been shown to be as effective as LMWH/VKAs, and maybe safer. Determining the optimal duration of treatment for a first unprovoked PE remains a challenge, although clinical prediction rules for estimating the risk of recurrence of venous thromboembolism and anticoagulation-associated haemorrhage are under investigation. Using these prediction rules may lead to both more standardized and more individualized long-term treatment of PE.

Impact of d-Dimer Levels on Admission on Inhospital and Long-Term Outcome in Patients With Type A Acute Aortic Dissection

Limited studies with relatively small sample sizes have reported that elevated d-dimer levels on admission were associated with increased risk of short-term mortality in patients with type A acute aortic dissection (AAD). However, there were unavailable data regarding the impact of admission d-dimer levels on long-term outcomes. Our present study aimed to evaluate the association of admission d-dimer levels with both inhospital and long-term all-cause mortality in patients with type A AAD. A total of 212 consecutive patients with type A AAD were enrolled. d-Dimer levels were measured on admission, and patients were followed up prospectively. The primary end points were inhospital and long-term all-cause mortality. The median length of follow-up was 18.8 months (interquartile range 6.7 to 24.4 months). The inhospital and long-term all-cause mortality rates were 12.7% and 12.4%, respectively. Compared with the survivors, the nonsurvivors had significantly higher d-dimer levels (p <0.001). When divided into 4 groups according to admission d-dimer quartiles, patients in Q4 (>6.10 μg/ml) had the highest inhospital and long-term mortality among groups. After multivariate adjustment, the d-dimer level in Q4 (>6.10 μg/ml) was an independent risk factor for inhospital mortality (hazard ratio [HR] 6.12, 95% confidence interval 1.35 to 27.89, p = 0.019) in addition to surgical treatment; however, this was not an independent predictor for long-term mortality. In conclusion, our study with a relatively large sample size suggested that elevated admission d-dimer levels (>6.10 μg/ml) might be a predictor for increased risk of inhospital mortality, and urgent-emergent surgery might be needed in patients with elevated d-dimer levels on admission. However, d-dimer levels at admission failed to predict long-term mortality.

Fibrinolysis and the control of blood coagulation

Fibrin plays an essential role in hemostasis as both the primary product of the coagulation cascade and the ultimate substrate for fibrinolysis. Fibrinolysis efficiency is greatly influenced by clot structure, fibrinogen isoforms and polymorphisms, the rate of thrombin generation, the reactivity of thrombus-associated cells such as platelets, and the overall biochemical environment. Regulation of the fibrinolytic system, like that of the coagulation cascade, is accomplished by a wide array of cofactors, receptors, and inhibitors. Fibrinolytic activity can be generated either on the surface of a fibrin-containing thrombus, or on cells that express profibrinolytic receptors. In a widening spectrum of clinical disorders, acquired and congenital defects in fibrinolysis contribute to disease morbidity, and new assays of global fibrinolysis now have potential predictive value in multiple clinical settings. Here, we summarize the basic elements of the fibrinolytic system, points of interaction with the coagulation pathway, and some recent clinical advances.

Performance of a diagnostic algorithm based on a prediction rule, D-dimer and CT-scan for pulmonary embolism in patients with previous venous thromboembolism. A systematic review and meta-analysis

Diagnostic management of suspected pulmonary embolism (PE) in patients with a history of venous thromboembolism (VTE) is complicated due to persistent abnormal D-dimer levels, residual embolic obstruction and higher clinical prediction rule (CPR) scores. We aimed to evaluate the safety and efficiency of the standard diagnostic algorithm consisting of a CPR, D-dimer test and computed tomography pulmonary angiography (CTPA) in this specific patient category. We performed a systematic literature search for prospective studies evaluating a diagnostic algorithm in consecutive patients with clinically suspected PE and a history of VTE. The VTE incidence rates during three-month follow-up and the number of indicated CTPAs were pooled using random effect models. Four studies concerning 1,286 patients were included with a pooled baseline PE prevalence of 36 % (95 % confidence interval [CI] 30-42). In only 217 patients (15 %; 95 %CI 11-20) PE could be excluded without CTPA. The three-month VTE incidence rate was 0.8 % (95 %CI 0.06-2.4) in patients managed without CTPA, 1.6 % (95 %CI 0.3-4.0) in patients in whom PE was excluded by CTPA and 1.4 % (95 %CI 0.6-2.7) overall. In the pooled studies, PE was safely excluded in patients with a history of VTE based on a CPR followed by a D-dimer test and/or CTPA, although the efficiency of the algorithm is relatively low compared to patients without a history of VTE.