Diagnostic Accuracy of D-dimer Testing and the Revised Geneva Score in the Prediction of Pulmonary Embolism

doi:10.21203/rs.3.rs-70153/v1

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Diagnostic Accuracy of D-dimer Testing and the Revised Geneva Score in the Prediction of Pulmonary Embolism

https://doi.org/10.21203/rs.3.rs-70153/v1

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Background. Pulmonary embolism (PE) diagnosis can sometimes be challenging due to the disease having nonspecific signs and symptoms at the time of presentation. The aim of the present study was to evaluate the validity of the D-dimer in combination with the revised Geneva score (RGS) in prediction of Pulmonary embolism.

Methods. This is a retrospective study of 2010 patients with suspected PE who had undergone both D-dimer testing followed by chest CT angiography (CTPA). The predictive accuracy of D-dimer, adjusted D-dimer and the revised Geneva score were calculated. ROC curve was applied to allocate the optimum RGS cutoff for PE prediction.

Results. Of all patients, the mean age was 52.2±20.2 years, two-thirds (65.1%) were females, with previous history of; DVT or PE (2%), surgery and/or fracture of lower limb (6.9%), active malignant conditions (14.4%), unilateral lower limb pain (0.6%), and hemoptysis (0.7%).The overall prevalence of PE was 16%. It was 0% in the low, 25.8% in intermediate and 88.9% in high clinical probability categories of RGS. Both conventional and age-adjusted D-dimer thresholds showed significant level of agreement (kappa=0.081, p<0.001), high sensitivity (94% & 92.8%), high NPV (91.2% & 91.4%), low specificity (12.3% & 15.3) and low PPV (17.5% & 17.8%), respectively. Combination of the age-adjusted D-dimer threshold and RGS at a cut-off of 5 points would provide 100% sensitivity and 61.7% specificity 34.1% PPV, 100% NPV and 0.87 AUC. At a RGS cutoff <5 points, PE could be have been excluded in 64.2% of patients with an abnormal age-adjusted D-dimer threshold without further imaging.

Conclusion. Conventional and age-adjusted D-dimer tests showed high levels of agreement in prediction of PE, high sensitivity and low specificity. RGS has a good performance in PE prediction. Application of a clinical decision rule, using the revised Geneva score, and age adjusted D-dimer threshold could increase the number of patients in whom PE could be excluded without further imaging.

Critical Care & Emergency Medicine

Validity

sensitivity

specificity

Deep vein thrombosis

agreement

clinical probability

D-dimer

age-adjusted threshold

Pulmonary Embolism (PE) is a disease that is commonly encountered in the emergency department [1-3]. The incidence of PE is estimated to be 60-70 per 100,000 general population [4]. In Saudi Arabia, the incidence of Venous Thromboembolism (VTE) comprised of PE and Deep Vein Thrombosis (DVT) is estimated to be approximately 100 per 100,000 per year, with an estimated number of 25,000 patients per year [2]. Its diagnosis can sometimes be challenging due to the disease having nonspecific signs and symptoms at the time of presentation [5]. The diagnosis can be made clinically using some validated risk assessment tools such as the Revised Geneva Score [6] and the Wells score [7] based on the signs and symptoms of the patient. After that, the next step would be obtaining a serum D-dimer level from the patient [8]. A negative result would rule out the possibility of having PE and would subsequently eliminate the need to use further confirmation by chest CT angiography (CTAP).

D-dimer levels have been shown to be affected by age [9,10] and many other variables such as malignancies and sepsis[9]. This Usually leads to unnecessary exposure to radiation while undergoing CTPA with studies showing that only 20% of those show positive result [11]. The overuse of CTPA [12] has been discussed in studies before highlighting that it has many disadvantages such as its effect in the patients. A study has shown that a single CTPA was associated with an average lifetime risk for cancer of 57/100,000 for females aged 17–19 years to 8/100,000 for males and females aged 80–89 years [13]. Furthermore, the use of CPTA holds up the efficacy and the flow of the ER by taking up beds for an unnecessary amount of time.

Many studies have come to the conclusion that the use of the age-adjusted D-dimer level in patients > 50 years old with low to moderate clinical probability to develop PE is safe and reduces the need to use unnecessary CTPA [14-16]. The use of age-adjusted D-dimer cutoff value (patient’s age x 10 μg/L), It has been shown that patients (42%) aged more than 50 years old with low clinical probability had PE excluded in comparison with patients (36%) when fixed D-dimer cutoff value (500 μg/L) was applied [13]. A case report with a patient older than 50 years who had an age-adjusted d-dimer level below the threshold and tested positive for PE later on has raised a point regarding the possibility of a false negative result [17]. One research compared the age-adjusted D-dimer level with a Clinical Probability Adjusted D-dimer level (1000 μg/L for low probability and 500 μg/L if intermediate), with a conclusion that the age-adjusted test is the preferred choice since it had a better Negative predictive value [18].

The Aims of this study were 1) to compare the diagnostic accuracy of conventional D-dimer level with that of the age-adjusted D-dimer level, and 2) to determine the diagnostic accuracy of using the age-adjusted D-dimer level, in combination with the revised Geneva Score, for prediction and/or exclusion of PE, and 3) to estimate the amount of unnecessary exposure of patients to radiation, in adults who underwent CTPA in the past three years in King Abdulaziz Medical City, Riyadh, Saudi Arabia. The results of this study would help in revising the policy and procedures of management of patients with suspected PE in our health facility.

This is a retrospective study of 2010 patients with suspected PE who had undergone both D-dimer testing followed by chest CT angiography (CTPA) over a period of 3 years, from January 2016 to January 2019. Patient’s charts from hospital records (Best-Care) were reviewed and information was extracted using a data collection sheet. The study was conducted at the Emergency Care Center (ECC), King Abdulaziz Medical City (KAMC) in the central region of Saudi Arabia. KAMC is the largest health institution of the Ministry of National Guard Health Affairs (MNG-HA). MNG-HA provide healthcare services to national guard service members and their dependents through large medical cities located in the 3 most densely populated regions of KSA, namely the Central, Western and Eastern regions. All facilities have been Joint Commission International (JCI) accredited since 2006.

ECC provides services for a rapidly growing patient population in all of its catchments areas, and it’s considered as the largest emergency care in Riyadh with a capacity of 125 beds and an ability to be increased if needed. The center has been established to provide urgent care services for all patients mainly trauma and critical medical cases. The center contains trauma X-Ray and Stat Lab to be ready when time becomes critical. It is divided into two main sections; Adult care: (30 consultants & 34 Staff Physicians) and Pediatric care (20 consultants & 21 Staff Physicians). The average number of ECC visits is about 700 patients per day with some seasonal variations. Access to emergency services is determined by a process of ED triage. At triage, nurses assign an urgency rating according to observable physiological parameters.15 ECC follows the Canadian ED Triage and Acuity scale (CTAS) guidelines in categorizing cases, based on the severity of the cases.

All patients, Saudis and non-Saudis, ages 18 years or more, of both sexes were included. The following data was collected: Gender, D-dimer level, Result of the Chest CT Angiography, and elements of the Revised Geneva Score (age, previous PE/ DVT, surgery/lower limb or fracture in the past month, having active malignancy, unilateral lower limb pain, hemoptysis, Heart rate and pain on limb palpation) [19].

Operational definitions

Acute PE refers to obstruction of pulmonary artery or one of its branches by material (eg; thrombus, tumor, air, or fat) that originated elsewhere in the body. A value of D-Dimer above 500 FEU (0.5µg/mL) was considered the cutoff value above which imaging modality was mandated. Age –adjusted D-Dimer threshold was calculated by multiplying the age of the patient 50 years and above by 10 [Age-adjusted D-Dimer (FEU) =Patient’s age x10). Or [Age-adjusted D-Dimer (µg/mL) = (Patient’s age x10)/1000].

Data analysis

Data was entered and analyzed using SPSS software version 26. Quantitative variables were expressed as means and standard deviation. Categorical values were expressed as frequencies and percentages. Sensitivity, Specificity, NPV, PPV were calculated for the diagnostic test results. The level of agreement between conventional and age-adjusted D-dimer was calculated with kappa. Estimation of the amount of unnecessary exposure to radiation was done by calculation of the percentage of patients with positive age-adjusted D-Dimer and did not have PE by CTPA. Receiver Operator Characteristic curve was applied to allocate the optimum RGS cutoff for the exclusion of PE. Significance was considered at p-value of <0.05.

Of 2010 patients with an average age of 52.2±20.2 years, two-thirds (65.1%) were females, with previous history of; DVT or PE (2%), surgery and/or fracture of lower limb (6.9%), active malignant conditions (14.4%), unilateral lower limb pain (0.6%), and hemoptysis (0.7%), (Table 1). A total of 332 (16.5%) patients were diagnosed as PE patients by CTPA. Sensitivity of conventional D-dimer for PE was high (94%), with only 20 false negative (1.0%), decreasing slightly to 92.8%, with 24 (1.2%) false negatives. Specificity of D-dimer for PE was low by the conventional threshold (12.3%), increasing to 15.3% by the age-adjusted threshold, Table 2. False negative rates were 1.0% and 1.2% for the conventional and age-adjusted thresholds, respectively.

The level of agreement between conventional D-dimer and age-adjusted D-dimer testing in prediction of PE was high [(976+98)/1128) x 100=95.2%, kappa=0.081, p<0.001]. Both thresholds agree on 100% [(8+90)/(8+90)] of negative cases, and 97.3% [(181+795)/(185+845)] of positive cases. Agreement in Positive CTPA is 95.5% [(181+8)/198], and agreement in negative CTPA is 94.7% [(795+90)/935]. In total, 98 patients had a D-dimer below the conventional threshold of 0.5Un, and 8 PE patients of them (8.2%) were missed. Meanwhile, 152 patients had a D-dimer below the age-adjusted threshold, 12 PE patients were missed (7.9%), Table 3.

According to the RGS, 747 patients (37.2%) had a low clinical probability, 1254 (62.4%) an intermediate clinical probability, and 9 (0.4%) a high clinical probabilities (Table 3), The prevalence of PE was 0%, 25.8% and 88.9% in these three different probability groups respectively, Table 4. The receiver operating characteristic curve was applied for allocation of an optimum RGS cut off for the prediction of PE (figure1). The cutoff ≥5 points was the optimum RGS cutoff for prediction of PE, with 100% sensitivity, 61.7% specificity, 34.1% PPV and 100% NPV, and an area under the curve of 0.87, Table 4.

An RGS <5 points and an age-adjusted D-dimer would have led to 562 fewer CTPA at a cost of no missed PEs. Among patients with positive D-Dimer (N=860), 308 (35.8%) had PE, whereas the remaining 552 (64.2%) did not have PE, and PE could have been ruled out for them without further imaging, with no missed PEs, Table 5.

In this study, the prevalence of PE was 16.5% among patients with suspected PE. This prevalence was comparable with an incidence of 16% In a previous study by Klok et al.,[20] and it ranged from 10.1% to 20.7% in other studies [13,21,22]. Clinical assessment of the probability of PE is important in the diagnostic approach of PE. Applying a clinical decision rule in combination with the age adjusted D-dimer threshold would have raised the number of PE ruled out patients without further imaging. According to the RGS, 747 patients (37.2%) had a low clinical probability, 1254 (62.4%) an intermediate clinical probability, and 9 (0.4%) a high clinical probabilities (Table 3), The prevalence of PE was 16.5%, 0%, 25.8% and 88.9% in these three different probability groups respectively. The corresponding prevalence figures were; 9%, 30% and 68% as reported in the Postoperative Investigation of Pulmonary Embolism Diagnosis (PIOPED) study [23], and 8.3% 22.8% and 71.4% as reported by Klok et al.[20] who concluded that PE could be excluded in patients with a low or intermediate clinical probability by RGS and a normal D-dimer level. However, from the results of our study, it would be safe to exclude PE in patients by a low clinical probability by the revised Geneva score irrespective of D-dimer results.

ROC curve was applied to allocate the optimum RGS cutoff for PE exclusion. It showed the cutoff of >5 points was the optimum RGS cutoff for prediction of PE, with 100% sensitivity, 61.7% specificity, 34.1% PPV and 100% NPV, and an area under the curve of 0.87. Douma et al [24] have validated the RGS two category scale of ≤5 and >5, on 807 patients with suspected PE and found only 1 PE among 185 patients who were PE unlikely and had a normal dimer. According to the findings of our study, at this cutoff <5, PE could have been excluded even with an abnormal age-adjusted D-dimer threshold, with no missed PE cases. This would have saved the cost of 1036 (51.5%) of CTPAs. Of 1730 patients whose age adjusted D-dimer threshold was abnormal, only 860 patients (50%) could have been tested by CTPA, while for the remaining 870 (50.2%) cases whose clinical probability was unlikely, PE could have been ruled out without further imaging. This finding was in agreement with the finding of a previous study that reported that using the RGS and a rule-out cut point of ≤ 5, 62 patients of 102 patients (60.8%) would have been spared CTPA at a cost of no PEs missed [25]

Our study showed that both conventional and age-adjusted thresholds had high sensitivity and low specificity, with a slightly increased specificity from 12.3% by conventional threshold to 15.3% by the age-adjusted threshold. This finding is in agreement with the findings of a retrospective study in Scotland [25], which reported an increased specificity from 11% to 24.9%. In the present study, among patients aged 50 years or more, 8 and 12 PE patients were missed, as false negatives, by the conventional and the age-adjusted thresholds, respectively. False negative rates ranged from 0.0- 0.6% using a conventional threshold, and 0.2-0.8% using an age-adjusted threshold.[13,21,22]. In our study, the corresponding rates were 1.0% and 1.2% for conventional and age-adjusted thresholds, respectively.

This study has some limitations. This study is based on data from one tertiary hospital in Saudi Arabia, and this may not allow for generalization of the conclusion. Moreover, it is a retrospective study from patients’ records, and may make it liable to some information biases. Large scale prospective studies, targeting the whole Saudi Arabia may be necessary.

The finding of this study confirm the fact that applying a clinical decision rule in combination with an age-adjusted D-dimer threshold would have increased the number of patients in whom PE could have been spared CTPA. Using the RGS and a rule-out cutoff <5 points, 870 patients would have been spared CTPA with no cost of PEs missed. It seems safe to withhold oral anticoagulation therapy in patients with suspected PE, if RGS is low according to the 3 risk category scale, or unlikely (<5 points) according to the 2 risk category scale.

Ethics approval and consent to participate

This study was approved by the institutional review board of the MNG-HA in Riyadh, Saudi Arabia (RC19/020/R). There was no need for consenting by patients as the study was done by retrieving data from medical records with no personal identifiers, and waiving of consent was approved by the IRB committee.

Consent for publication

Not applicable

Availability of data and materials

Most of the data supporting our findings is contained within the manuscript, and all others, excluding identifying/confidential patient data should, will be shared upon request.

Competing interest

The authors declare that they have no competing interests.

Funding

None

Author contributions

MAA contributed to concept development, manuscript preparation and final writing, KA and MAA contriputed to concept development and data collection, MAA contributed to concept development statistical analysis and manuscript finalization, and KA and MAA contributed to research proposal writing, data collection, analysis and interpretation, and manuscript drafting. All authors read and approved the final manuscript.

Acknowledgements

This study was initiated by King Abdullah International Medical Research Center, King Saud bin Abdulaziz University for Health Sciences, Riyadh, Saudi Arabia. The final draft of the manuscript was English language edited by Macmillan Science Communication

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Table 1. Personal and clinical characteristics of the study sample

Characteristics	Total (N=2010)
Age (years), mean (SD)	52.6 (20.2)
Sex: Female/Male	1290/720 (1.8)
Clinical characteristics: 1. Age >65 years 2. Previous DVT or PE	595 (29.6) 41 (2.0)
3. Surgery (under general anaethesia) or fracture of lower limbs within 1 month	138 (6.9)
4. Active malignant conditions	293 (14.6)
5. Unilateral lower-limb pain	12 (0.6)
6. Hemoptysis	14 (0.7)
7. Heart rate 75-94 beats/ min.	1330 (66.2)
Heart rate >95 beats/ min.	680 (33.8)
8. Pain on lower-limb deep venous palpation and unilateral edema	0 (0.0)
Revised Geneva Score (clinical probability) Geneva Low score (0-3)	747 (37.2)
Geneva Intermediate score (4-10)	1254 (62.4)
Geneva High score (more than 10)	9 (0.4)

DVT, deep vein thrombosis; PE, pulmonary embolism.

Table 2. Comparison between conventional D-dimer and age-adjusted D-dimer in accuracy of prediction of pulmonary embolism

	Chest CT scan
	Positive no.(%)	Negative no.(%)	Total no.(%)
Conventional D-dimer
Abnormal	312 (15.5)	1472 (73.2)	1784 (88.8)
Normal	20 (1.0)	206 (10.2)	226 (11.2)
Total	332 (16.5)	1678 (83.5)	2010
Sensitivity=94%, specificity= 12.3%, PPV=17.5%, NPV= 91.2, kappa=0.009, p=0.001
Age-adjusted D-dimer
Abnormal	308 (15.3)	1422 (70.7)	1730 (86.1)
Normal Total	24 (1.2) 332 (16.5)	256 (12.7) 1678 (83.5)	280 (13.9) 2010
Sensitivity= 92.8%, specificity= 15.3%, PPV= 17.8%, NPV= 91.4%, kappa= 0.030, p<0.001.

Table 3. Performance and level of agreement between D-dimer and age-adjusted D-dimer testing in the prediction of pulmonary embolism

	Age-adjusted D-dimer		Total
Conventional D-dimer	Abnormal	Normal	Total
	n. PE	n. PE	n. PE
Abnormal	976 181	54 4	1030 185 (18.0)
Normal	o 0	98 8	98 8 (8.2)
Total	976 181(18.5)	152 12(7.9)	1128 193 (17.1)

PE, pulmonary embolism.

Table 4. Prevalence of pulmonary embolism in patients with different revised Geneva score categories and validity of a cutoff of 5 Revised Geneva score ≥5 in the prediction of pulmonary embolism

Revised Geneva Score (3 categories)	Chest CT scan
	Positive	Negative	Total
	no.(%)	no.(%)	no.(%)
Low	0 (0.0)	747 (100.0)	747 (37.2)
Intermediate	324(25.8)	930 (74.2)	1254 (62.4)
High	8 (88.9)	1 (11.1)	9 (0.4)
	332 (16.5)	1678 (83.5)	2010 (100.0)
Revised Geneva score (2 categories)	Chest CT scan
Revised Geneva score (2 categories)	Positive no.(%)	Negative no.(%)	Total no.(%)
Likely (5 points or more)	332 (100.0)	642 (38.3)	974 (48.5)
Unlikely (<5 points)	0 (0.0)	1036 (61.7)	1036 (51.5)
Total	332	1678	2010
Sensitivity=100%, specificity= 61.7%, PPV=34.1%, NPV= 100, kappa=0.35, p=<0.001

Table 5. Application of a clinical decision rule and age adjusted D-dimer threshold for prediction of PE.

Age-adjusted D-dimer	Revised Geneva Score	No. of patients	PE patients No.(%)
Abnormal	Likely (>5points)	860	308 (35.8)
Abnormal	Unlikely (≤5points)	870	0 (0.0)
Normal	Likely (>5points)	114	24 (21.1)
Normal	Unlikely (≤5points)	166	0 (0.0)

PE, pulmonary embolism.

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Diagnostic Accuracy of D-dimer Testing and the Revised Geneva Score in the Prediction of Pulmonary Embolism

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