Comparison of 2-Point and 3-Point Point-of-Care-Ultrasound Techniques for Deep Vein Thrombosis In the Emergency Department
Bilal Zeftawi, MD
Published Feb. 20, 2021
Probetrotters | Journal Article Review
Article
Lee JH, Lee SH, Yun SJ. Comparison of 2-point and 3-point point-of-care ultrasound techniques for deep vein thrombosis at the emergency department: A meta-analysis. Medicine (Baltimore). 2019 May;98(22):e15791. doi: 10.1097/MD.0000000000015791. PMID: 31145304; PMCID: PMC6709014.
Background
Point of Care Ultrasound (POCUS) can be used to assess the presence of thrombosis within the venous system. In normal physiology, veins and arteries can be easily differentiated based on structure, wall thickness, and compressibility. Arteries tend to take on a rigid circular shape with thick wall that are generally noncompressible. In comparison, veins will be floppy irregular shaped with thin walls that are easily collapsible with pressure (Figure 1a). However, in the presence of venous thrombosis, veins will lose their compressibility due to containing a space occupying thrombus (Figure 1b). It is this distinction that allows the sonographer to determine the presence of a vein thrombosis.
Clinically speaking, not all venous thrombi are considered equal and the distinction depends on the location of the thrombus. Superficial vein thrombus (SVT) are thrombi that are located within the superficial compartment of an extremity and generally considered low risk for complications (great saphenous vein, small saphenous vein, anterior accessory saphenous vein, intersaphenous vein, with the exception of clots in the greater saphenous vein that are extremely close in proximity to the common femoral / great saphenous junction). Deep vein thrombosis (DVT) are thrombi located within the deep compartment and generally considered high risk for propagating into a pulmonary embolism which carries a high morbidity and mortality risk (common femoral vein, deep femoral vein, femoral vein, popliteal vein, gastrocnemius vein, tibial veins, fibular veins. These veins are shown in figure 2.
Study Design:
Meta-analysis study that pooled data comparing 2-point vs 3-point compression for DVT diagnosis
Objectives:
The objective is to compare the efficacy of POCUS for diagnosing DVTs by comparing the sensitivity, specificity, and false negative ratios of 2-point and 3-point compression
Methods:
This study analyzed data collected from PubMed, EMBASE, and Cochrane. It compared the POCUS technique in question to a higher diagnostic standard which included venography or formal radiologist study. The data was extracted and studied independently by 2 investigators. Any disagreements between the reviewers were resolved by discussion.
When evaluating for deep vein thrombosis, there are two different approaches that physician can perform. The 2-point and the 3-point that differ in the sites that are assessed. Both techniques utilize the same approach explained above to evaluate for a deep vein thrombus. However, they differ at the sites of evaluation as follows:
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2-Point POCUS (Figure 3a)
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Common Femoral Vein (into Saphenofemoral Vein)
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Popliteal Vein
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3-Point POCUS (Figure 3b)
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Common Femoral Vein
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Saphenofemoral Junction
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Popliteal Vein
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Inclusion Criteria
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Patients with suspected DVT
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Assessed by emergency medicine physicians ranging from residents to attendings
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Utilizing 2-point or 3-point compression with the plan of performing confirmatory duplex ultrasound studies
Exclusion Criteria
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Studies using alternative definitions of 2-point and 3-point compressions
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Studies using duplex ultrasound as the primary index test
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Studies not conducted by emergency medicine physicians
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Case reports, review articles, clinical trials, conference abstracts
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Letters, editorials, guidelines, consensus statements
What are some possible flaws in the methods used?
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Evaluators “discuss” disagreements, in a non-standardized format without clearly defined factors.
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Publication bias in which the prevalence of DVT in the studies might have been higher than that of the prevalence of DVT in the general population leading to a higher pre-test probability.
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Heterogenicity between studies that were not able to be screened for using the inclusion and exclusion criteria.
Limitations
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No recommendations on ways to improve the sensitivity/specificity between the 2 techniques.
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Relatively small number of total studies used in this this sample
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Heterogeneity among the sonographer’s years of experience between and within studies.
Results
2-point POCUS produced a sensitivity of 91% and specificity of 98% with a 4.0% false negative rate. The 3-point POCUS produced a sensitivity of 90% and a specificity of 95% with a 4.1% false negative rate. The difference in sensitivity, specificity and false negative rate were not statistically significant.
As for heterogeneity amongst the data, several factors were assessed using meta regression. There appeared to be variation among the location (United States vs Other countries), total patients studied, proportion of DVT among the patients, ratio of male-to-female ratio patients, and the experience of the sonographer. As for experience, it was determined that the years of experience, as defined by stage of training (resident vs attending), was proportional to the test sensitivity. This is to be expected as user proficiency is a caveat to many ultrasound studies.
Discussion
There is no statistical significance when comparing the 2-point and 3-point POCUS for the evaluation of DVT. The time it takes to conduct a 2-point POCUS was less than that of the 3-point POCUS. The years of experience that the sonographer has trained was a statistically significant factor that determined sensitivity suggesting that user variability has a higher impact than specific test used. It can be theorized that a 3-point technique may have a higher false positive rate due to having more data to analyze and potentially lead to a positive rate.
Take Away Points:
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Both 2-point and 3-point POCUS yield similar efficacy in terms of sensitivity, specificity, and false negative rate in the diagnosis of DVTs.
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Overall, 2-point POCUS is recommended due to requiring less time than 3-point POCUS.
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The sonographer’s years of experience is positively correlated with the efficacy of the test.
Does this study influence your practice?
Overall, this study will have a minor influence my practice as an emergency medicine physician. Although time is often a limited commodity within the emergency department, it is important for physicians to use rationale when deciding a diagnostic approach rather than looking at the situation from the perspective of efficiency. For example, research has showed that SVTs located within 3-4cm of a deep vein structure pose a higher risk of propagation and should be treated analogously to a DVT (Cosmi, 2015). Likewise, it was found that treating SVTs >5cm resulted in lower morbidity and mortality due to PE risk (Chowla, 2012). Therefore, in cases like these, a 3-point approach is more likely to identify this risk while it is still technically categorized as a SVT. Furthermore, by foregoing the saphenofemoral junction, the 2-point approach will miss about 10-15 cm of the femoral vein which can be evaluated. With that in mind, I will most likely still favor data produced by the 3-point approach over the 2-point approach.
[1] Cosmi, B. (2015). Management of superficial vein thrombosis. Journal of Thrombosis and Haemostasis, 13(7), 1175-1183.
[2] Chowla, A. (2012). Superficial Venous Thrombophlebitis (SVT): To Refer or Not to Refer?. The Official Journal of Center for Vein Restoration, 5(4).
[3] Lee JH, Lee SH, Yun SJ. Comparison of 2-point and 3-point point-of-care ultrasound techniques for deep vein thrombosis at the emergency department: A meta-analysis. Medicine (Baltimore). 2019 May;98(22):e15791. doi: 10.1097/MD.0000000000015791. PMID: 31145304; PMCID: PMC6709014.
[4] Scovell, S. (2018). Phlebitis and thrombosis of the superficial lower extremity veins.