1426
Correspondence / American Journal of Emergency Medicine 32 (2014) 1413–1432
pneumothorax based on the combination of 4 signs that mainly emerged during the last decade is intuitive [3]. The sensitivity and specificity of lung ultrasound for pneumothorax are based on the evidence of several original studies published in high-ranking international peer-reviewed journals and cannot be considered “highly questionable”. Rea et al allusions to “methodological limitations” are supported only by 2 articles that are not original studies and represent exceptions in the modern literature. Apart from many obvious methodological flaws, the review article of Sperandeo et al, reference number 2 in the letter, is based on personal opinions and does not reference the vast majority of literature, including the document that lists the recommendations on point-of-care lung ultrasound agreed by a qualified international scientific community [4]. The other reference, number 5 in the letter, is the document of the British Thoracic Society that lists the recommendation for pleural procedures and the use of thoracic ultrasound as a guide but does not specifically analyze the ultrasound diagnosis of pneumothorax. It is true that, in a very short and secondary paragraph of the document, the British Thoracic Society experts question on the usefulness of lung ultrasound for pneumothorax. However, their conclusion appears to be based on a small study of 11 patients from 1986 to 1989, 2 small studies with only 4 pneumothoraces in one and another small series whose ultrasounds were retrospectively reviewed. Against these small and somewhat dated studies, a large number of recent investigations support a quite different conclusion. This concern was strongly addressed in the letter that the international scientific board of the consensus conference on point-of-care lung ultrasound sent to Thorax journal [5]. Second point: the double lung point is a condition that does not undermine the main principles of lung ultrasound for pneumothorax. Absence of sliding without B-lines and pulse (the A-lines pattern) and visualization of the lung point feature the ultrasound pattern of pneumothorax [4]. Contusions and adherences cannot be misdiagnosed because in these conditions the consolidation and/or focal B-lines and/ or irregularity of the pleural line are still visible, even in the absence of sliding, whereas the lung point cannot be detected [6]. Thus, the case report of Aspler et al cannot question the accuracy of lung ultrasound for pneumothorax. Rather, it raises the problem of small loculated pneumothorax that sometimes may only be detected by extending the ultrasound evaluation to the whole chest [7]. In these cases, the double lung point is often a specific sign [8]. Sensitivity of lung sliding for pneumothorax still remains very high because when the sliding is visualized, it rules out pneumothorax in the chest area where the probe is placed. Even considering rare false-negative cases, on occasion due to small loculated pneumothorax that may be misdiagnosed when the chest is not fully explored, sensitivity of lung ultrasound is far superior to supine chest radiography and has a similar very high specificity [3]. In conclusion, I would assert that cases showing double lung point will not “preclude to trust in thoracic ultrasound practice”. There is sufficient evidence in literature, also corroborated by experts opinion, to recommend the application of lung ultrasound for pneumothorax in the daily practice. Bedside lung ultrasound may save costs, time, radiations, and even lives when correctly applied in emergency and extreme emergency scenarios [9]. Giovanni Volpicelli, MD, FCCP Department of Emergency Medicine San Luigi Gonzaga University Hospital, Torino, Italy E-mail address: [email protected] http://dx.doi.org/10.1016/j.ajem.2014.08.031
References [1] Aspler A, Pivetta E, Stone MB. Double-lung point sign in traumatic pneumothorax. Am J Emerg Med 2014;32(819):e811–2.
[2] Rea G, D'Amato M, Ghittoni G. Pitfalls of the ultrasound diagnosis of pneumothorax. Am J Emerg Med 2014. http://dx.doi.org/10.1016/j.ajem.2014.03.053. [3] Volpicelli G. Sonographic diagnosis of pneumothorax. Intensive Care Med 2011;37: 224–32. [4] Volpicelli G, Elbarbary M, Blaivas M, Lichtenstein DA, Mathis G, Kirkpatrick AW, et al. International evidence-based recommendations for point-of-care lung ultrasound. Intensive Care Med 2012;38:577–91. [5] Agricola E, Arbelot C, Blaivas M, Bouhemad B, Copetti R, Dean A, et al. Ultrasound performs better than radiographs. Thorax 2011;66:828–9 [author reply 829]. [6] Volpicelli G, Cardinale L, Berchialla P, Mussa A, Bar F, Frascisco MF. Am J Emerg Med 2012;30:317–24. [7] Volpicelli G, Boero E, Stefanone V, Storti E. Unusual new signs of pneumothorax at lung ultrasound. Crit Ultrasound J 2013;5:10. [8] Volpicelli G, Audino B. The double lung point: an unusual sonographic sign of juvenile spontaneous pneumothorax. Am J Emerg Med 2011;29(355):e351–2. [9] Volpicelli G. Usefulness of emergency ultrasound in nontraumatic cardiac arrest. Am J Emerg Med 2011;29:216–23.
Questioning the ultrasound diagnosis of pneumothorax
To the Editor, We 3 MDs (a radiologist, a pneumologist, and an intervention ultrasound internist working also in the emergency department) practice in well-known, very active, and historical European cardiothoracic institutions. In our original letter [1], we very respectfully suggest a different interpretation of the published computed tomography (CT) images and of the ultrasound videoclip by Aspler et al [2]. The elegant answer of Aspler et al [3] to our letter [1] is constructive and contributory to the debate and the readers' understanding. Aspler et al wrote “the transmitted still image of the CT may prove difficult to appreciate the extent of the pneumothorax… we do not shy away from acknowledging that alternative diagnoses, such as pleural adhesion, may be possible despite the CT diagnosis and are careful to not overstate our conclusions....the patient was otherwise healthy with no history of smoking, asthma, chronic obstructive pulmonary disease, pulmonary fibrosis, thoracic surgery, cancer, nor any other reason to suspect an alternative pathology.” There is obviously no problem because what we [1] see and what the reader understands is that Aspler et al are appropriately describing a very particular case because “Volpicelli et al have alluded to double lung point sign in trauma, and nobody has yet published a report with CT imaging confirming the diagnosis.” This is all. A case report of a small pneumothorax with, for the first time, the availability of a CT image displayed as an integration of a previous case report of somebody else. Why is Dr Volpicelli so straightforwardly quoting their appeal letter against the “document” of the British Thoracic Society (the official recommendation of the British Thoracic Society published on Thorax)? [4]. We note that Dr Volpicelli coauthored a letter very similar to this one in Thorax, along with many authors, which were a group of emergency physicians claiming to have published recommendations on point-of-care lung ultrasound. The “British” answer in Thorax was very polite and addressed the origin of those recommendations: “we maintain that the medical community should proceed with caution when using ultrasound in the detection and management of pneumothoraces. If the reviews referenced are not considered, 13 of the remaining 24 papers referenced are in two welldefined patient groups, trauma and postintervention. None of the papers published prospectively demonstrated improved outcomes and management change using ultrasound in comparison with chest x-ray (CXR), and perhaps more significantly, only one prospective blinded study in medical patients with varying degrees of respiratory compromise has been reported and this demonstrated an unacceptably high false-positive rate. We maintain that ultrasound is limited in its usefulness in the assessment of cases of spontaneous pneumothorax and following pleural procedures particularly in settings outside
Correspondence / American Journal of Emergency Medicine 32 (2014) 1413–1432
critical care. Many of these patients have underlying lung disease, particularly chronic obstructive pulmonary disease, which reduces the accuracy of pneumothorax detection by ultrasound. If a pneumothorax is detected by ultrasound, a CXR is usually required to assess its size (unless a CT scan is then performed)” and to detect comorbidities involving diaphragm, mediastinum, aortic arch, and nonsubpleural lung. The Editor of Thorax required also this statement for that letter: “Competing interests. This letter is being written on behalf of the Winfocus International Liaison Committee on Pleural and Lung Ultrasound (ILCPLUS). The goal of this group is to promote the use of point of care ultrasound although none of the members has any specific financial conflicts.” In conclusion, it should be noted that British radiologists, including Fergus Gleeson, Oxford University's Professor of Radiology, commented, as we did in our letter: “If the pneumothorax is so small as to be undetectable on CXR, then it is unlikely to require intervention and the use of ultrasound will not have changed the management” [4]. This last magical sentence is in agreement with Aspler et al [2,3] and with us [1]. “Elementary my dear Watson” as Sherlock Holmes would say.
Rea Gaetano, MD Department of Radiology, Ospedali dei Colli, A.O. Monaldi, Naples, Italy Corresponding author. E-mail addresses: [email protected], [email protected] Maria D’Amato, MD Department of Pneumology, Ospedali dei Colli, A.O. Monaldi Naples, Italy Giorgia Ghittoni, MD Department of Medicine, I.R.C.C.S. Policlinico San Matteo, Pavia, Italy
http://dx.doi.org/10.1016/j.ajem.2014.08.025 References [1] Rea G, D'Amato M, Ghittoni G. Pitfalls of the ultrasound diagnosis of pneumothorax. Am J Emerg Med 2014. http://dx.doi.org/10.1016/j.ajem.2014.03.053 [pii:S07356757(14)00419-7, Epub ahead of print]. [2] Aspler A, Pivetta E, Stone MB. Double-lung point sign in traumatic pneumothorax. Am J Emerg Med 2014;32:819.e1–2. [3] Aspler A, Stone MB. Pitfalls in the ultrasound diagnosis of pneumothorax: the authors respond. Am J Emerg Med 2014. http://dx.doi.org/10.1016/j.ajem.2014.03. 044 [pii:S0735-6757(14)00232-0, Epub ahead of print]. [4] Havelock T, Teoh R, Laws D, Gleeson F, BTS Pleural Disease Guideline Group. Pleural procedures and thoracic ultrasound: British Thoracic Society. Pleural Disease Guideline. Authors' response. Thorax 2011;66:829.
Let us publish D-dimer in micrograms per liter☆
To the Editor, D-dimer (DD) is very useful in a variety of clinical scenarios, for example, to rule out pulmonary thromboembolism (PTE) and aortic dissection (AoD) in low-risk patients [1,2]. For both of these conditions, the usual cut-off between normal and pathologic values is a DD level of 500 ng/mL [1,3]. In addition, if DD level is greater than 1600 ng/mL, it may also rule in AoD [3]. The number of published articles focusing on DD in PubMed is high: 6913 from 1975 until now, out of which 611 in 2013
☆ This work has been supported by the Serbian Ministry of Education and Science (Belgrade, Serbia), grant no. III41018.
1427
(search performed on 8/12/2014). However, the difficulty in assessing and comparing the results of these studies is the fact that, to date, at least 10 different numerical units have been used to express DD results. Before 2013, at least 9 different numerical units were used for DD in medical literature [4]. During 2013, the number was also 9 (PubMed search performed on 8/12/2014, too): milligrams per deciliter [5], milligrams per liter [6], micrograms per milliliter [7], micrograms per deciliter [8], micrograms per liter [3], nanograms per milliliter [9], nanograms per deciliter [10], nanograms per liter [11], and picograms per milliliter [12]. Moreover, 1 additional numerical unit appeared in 2014: milligrams per milliliter [13]. Taken together, during the last 18 months alone, at least 10 different DD units (DDUs) have been used in medical publications. In addition, number of units may actually be twice as high (even 20) because DD can be reported in 2 different measurement types: DDU or fibrinogen equivalent units, with 1 DDU being equivalent to 2 fibrinogen equivalent units [14]. We therefore suggest that the preferable unit for DD should be either nanograms per milliliter or the equivalent micrograms per liter because of the following: (1) The normal concentration can be expressed as the whole positive number (230 ng/mL seems better than 0.230 μg/mL, although both reflect the same concentration); (2) Upper normal limit suggested by the international guidelines for PTE and AoD is 500 in ng/mL [1] and 500 μg/L [3]; (3) Age-adjusted cut-off for PTE/venous thromboembolism was suggested to be calculated as: number of patients' years × 10 (in micrograms per liter) [15]; and (4) Approximately 51% of the publications (available in PubMed) express the results as nanograms per milliliter. PubMed search, performed on August 12, 2014, resulted in the following number of publications with different numerical DDUs: milligrams per deciliter was used in 107 publications, milligrams per liter in 201, micrograms per milliliter in 85, micrograms per deciliter in 2, micrograms per liter in 44, nanograms per milliliter in 573, nanograms per deciliter in 16, nanograms per liter in 26, and picograms per milliliter in 71. To conclude, no less than 10 various units have been used for DD in the last 18 months. We suggest the preferable unit for DD should be (the most commonly used) nanograms per milliliter, but there is even more suitable unit: micrograms per liter because the values expressed in nanograms per milliliter and micrograms per liter are numerically equal, and the second one is directly in liter, not derived unit. The standardization of the DDUs is essential in achieving easy and accurate interpretation and more importantly comparison of DD results. We can afford ourselves the unification of DDUs at no cost. Acknowledgment The author thank Associate Professor Vera Ignjatovic PhD, BSc (Hons), cogroup leader, Haematology Research, Murdoch Childrens Research Institute; principal fellow, Department of Paediatrics, The University of Melbourne, Australia, for the scientific edit of the manuscript. Goran P. Koracevic, MD, PhD Department of Cardiology, Clinical Center and Medical Faculty University of Nis, Nis, Serbia E-mail address: [email protected] http://dx.doi.org/10.1016/j.ajem.2014.08.042 References [1] Torbicki A, Perrier A, Konstantinides S, Agnelli G, Galiè N, Pruszczyk P, et al. Task Force for the Diagnosis and Management of Acute Pulmonary Embolism of the European Society of Cardiology. Guidelines on the diagnosis and management of acute pulmonary
Correspondence / American Journal of Emergency Medicine 32 (2014) 1413–1432
pneumothorax based on the combination of 4 signs that mainly emerged during the last decade is intuitive [3]. The sensitivity and specificity of lung ultrasound for pneumothorax are based on the evidence of several original studies published in high-ranking international peer-reviewed journals and cannot be considered “highly questionable”. Rea et al allusions to “methodological limitations” are supported only by 2 articles that are not original studies and represent exceptions in the modern literature. Apart from many obvious methodological flaws, the review article of Sperandeo et al, reference number 2 in the letter, is based on personal opinions and does not reference the vast majority of literature, including the document that lists the recommendations on point-of-care lung ultrasound agreed by a qualified international scientific community [4]. The other reference, number 5 in the letter, is the document of the British Thoracic Society that lists the recommendation for pleural procedures and the use of thoracic ultrasound as a guide but does not specifically analyze the ultrasound diagnosis of pneumothorax. It is true that, in a very short and secondary paragraph of the document, the British Thoracic Society experts question on the usefulness of lung ultrasound for pneumothorax. However, their conclusion appears to be based on a small study of 11 patients from 1986 to 1989, 2 small studies with only 4 pneumothoraces in one and another small series whose ultrasounds were retrospectively reviewed. Against these small and somewhat dated studies, a large number of recent investigations support a quite different conclusion. This concern was strongly addressed in the letter that the international scientific board of the consensus conference on point-of-care lung ultrasound sent to Thorax journal [5]. Second point: the double lung point is a condition that does not undermine the main principles of lung ultrasound for pneumothorax. Absence of sliding without B-lines and pulse (the A-lines pattern) and visualization of the lung point feature the ultrasound pattern of pneumothorax [4]. Contusions and adherences cannot be misdiagnosed because in these conditions the consolidation and/or focal B-lines and/ or irregularity of the pleural line are still visible, even in the absence of sliding, whereas the lung point cannot be detected [6]. Thus, the case report of Aspler et al cannot question the accuracy of lung ultrasound for pneumothorax. Rather, it raises the problem of small loculated pneumothorax that sometimes may only be detected by extending the ultrasound evaluation to the whole chest [7]. In these cases, the double lung point is often a specific sign [8]. Sensitivity of lung sliding for pneumothorax still remains very high because when the sliding is visualized, it rules out pneumothorax in the chest area where the probe is placed. Even considering rare false-negative cases, on occasion due to small loculated pneumothorax that may be misdiagnosed when the chest is not fully explored, sensitivity of lung ultrasound is far superior to supine chest radiography and has a similar very high specificity [3]. In conclusion, I would assert that cases showing double lung point will not “preclude to trust in thoracic ultrasound practice”. There is sufficient evidence in literature, also corroborated by experts opinion, to recommend the application of lung ultrasound for pneumothorax in the daily practice. Bedside lung ultrasound may save costs, time, radiations, and even lives when correctly applied in emergency and extreme emergency scenarios [9]. Giovanni Volpicelli, MD, FCCP Department of Emergency Medicine San Luigi Gonzaga University Hospital, Torino, Italy E-mail address: [email protected] http://dx.doi.org/10.1016/j.ajem.2014.08.031
References [1] Aspler A, Pivetta E, Stone MB. Double-lung point sign in traumatic pneumothorax. Am J Emerg Med 2014;32(819):e811–2.
[2] Rea G, D'Amato M, Ghittoni G. Pitfalls of the ultrasound diagnosis of pneumothorax. Am J Emerg Med 2014. http://dx.doi.org/10.1016/j.ajem.2014.03.053. [3] Volpicelli G. Sonographic diagnosis of pneumothorax. Intensive Care Med 2011;37: 224–32. [4] Volpicelli G, Elbarbary M, Blaivas M, Lichtenstein DA, Mathis G, Kirkpatrick AW, et al. International evidence-based recommendations for point-of-care lung ultrasound. Intensive Care Med 2012;38:577–91. [5] Agricola E, Arbelot C, Blaivas M, Bouhemad B, Copetti R, Dean A, et al. Ultrasound performs better than radiographs. Thorax 2011;66:828–9 [author reply 829]. [6] Volpicelli G, Cardinale L, Berchialla P, Mussa A, Bar F, Frascisco MF. Am J Emerg Med 2012;30:317–24. [7] Volpicelli G, Boero E, Stefanone V, Storti E. Unusual new signs of pneumothorax at lung ultrasound. Crit Ultrasound J 2013;5:10. [8] Volpicelli G, Audino B. The double lung point: an unusual sonographic sign of juvenile spontaneous pneumothorax. Am J Emerg Med 2011;29(355):e351–2. [9] Volpicelli G. Usefulness of emergency ultrasound in nontraumatic cardiac arrest. Am J Emerg Med 2011;29:216–23.
Questioning the ultrasound diagnosis of pneumothorax
To the Editor, We 3 MDs (a radiologist, a pneumologist, and an intervention ultrasound internist working also in the emergency department) practice in well-known, very active, and historical European cardiothoracic institutions. In our original letter [1], we very respectfully suggest a different interpretation of the published computed tomography (CT) images and of the ultrasound videoclip by Aspler et al [2]. The elegant answer of Aspler et al [3] to our letter [1] is constructive and contributory to the debate and the readers' understanding. Aspler et al wrote “the transmitted still image of the CT may prove difficult to appreciate the extent of the pneumothorax… we do not shy away from acknowledging that alternative diagnoses, such as pleural adhesion, may be possible despite the CT diagnosis and are careful to not overstate our conclusions....the patient was otherwise healthy with no history of smoking, asthma, chronic obstructive pulmonary disease, pulmonary fibrosis, thoracic surgery, cancer, nor any other reason to suspect an alternative pathology.” There is obviously no problem because what we [1] see and what the reader understands is that Aspler et al are appropriately describing a very particular case because “Volpicelli et al have alluded to double lung point sign in trauma, and nobody has yet published a report with CT imaging confirming the diagnosis.” This is all. A case report of a small pneumothorax with, for the first time, the availability of a CT image displayed as an integration of a previous case report of somebody else. Why is Dr Volpicelli so straightforwardly quoting their appeal letter against the “document” of the British Thoracic Society (the official recommendation of the British Thoracic Society published on Thorax)? [4]. We note that Dr Volpicelli coauthored a letter very similar to this one in Thorax, along with many authors, which were a group of emergency physicians claiming to have published recommendations on point-of-care lung ultrasound. The “British” answer in Thorax was very polite and addressed the origin of those recommendations: “we maintain that the medical community should proceed with caution when using ultrasound in the detection and management of pneumothoraces. If the reviews referenced are not considered, 13 of the remaining 24 papers referenced are in two welldefined patient groups, trauma and postintervention. None of the papers published prospectively demonstrated improved outcomes and management change using ultrasound in comparison with chest x-ray (CXR), and perhaps more significantly, only one prospective blinded study in medical patients with varying degrees of respiratory compromise has been reported and this demonstrated an unacceptably high false-positive rate. We maintain that ultrasound is limited in its usefulness in the assessment of cases of spontaneous pneumothorax and following pleural procedures particularly in settings outside
Correspondence / American Journal of Emergency Medicine 32 (2014) 1413–1432
critical care. Many of these patients have underlying lung disease, particularly chronic obstructive pulmonary disease, which reduces the accuracy of pneumothorax detection by ultrasound. If a pneumothorax is detected by ultrasound, a CXR is usually required to assess its size (unless a CT scan is then performed)” and to detect comorbidities involving diaphragm, mediastinum, aortic arch, and nonsubpleural lung. The Editor of Thorax required also this statement for that letter: “Competing interests. This letter is being written on behalf of the Winfocus International Liaison Committee on Pleural and Lung Ultrasound (ILCPLUS). The goal of this group is to promote the use of point of care ultrasound although none of the members has any specific financial conflicts.” In conclusion, it should be noted that British radiologists, including Fergus Gleeson, Oxford University's Professor of Radiology, commented, as we did in our letter: “If the pneumothorax is so small as to be undetectable on CXR, then it is unlikely to require intervention and the use of ultrasound will not have changed the management” [4]. This last magical sentence is in agreement with Aspler et al [2,3] and with us [1]. “Elementary my dear Watson” as Sherlock Holmes would say.
Rea Gaetano, MD Department of Radiology, Ospedali dei Colli, A.O. Monaldi, Naples, Italy Corresponding author. E-mail addresses: [email protected], [email protected] Maria D’Amato, MD Department of Pneumology, Ospedali dei Colli, A.O. Monaldi Naples, Italy Giorgia Ghittoni, MD Department of Medicine, I.R.C.C.S. Policlinico San Matteo, Pavia, Italy
http://dx.doi.org/10.1016/j.ajem.2014.08.025 References [1] Rea G, D'Amato M, Ghittoni G. Pitfalls of the ultrasound diagnosis of pneumothorax. Am J Emerg Med 2014. http://dx.doi.org/10.1016/j.ajem.2014.03.053 [pii:S07356757(14)00419-7, Epub ahead of print]. [2] Aspler A, Pivetta E, Stone MB. Double-lung point sign in traumatic pneumothorax. Am J Emerg Med 2014;32:819.e1–2. [3] Aspler A, Stone MB. Pitfalls in the ultrasound diagnosis of pneumothorax: the authors respond. Am J Emerg Med 2014. http://dx.doi.org/10.1016/j.ajem.2014.03. 044 [pii:S0735-6757(14)00232-0, Epub ahead of print]. [4] Havelock T, Teoh R, Laws D, Gleeson F, BTS Pleural Disease Guideline Group. Pleural procedures and thoracic ultrasound: British Thoracic Society. Pleural Disease Guideline. Authors' response. Thorax 2011;66:829.
Let us publish D-dimer in micrograms per liter☆
To the Editor, D-dimer (DD) is very useful in a variety of clinical scenarios, for example, to rule out pulmonary thromboembolism (PTE) and aortic dissection (AoD) in low-risk patients [1,2]. For both of these conditions, the usual cut-off between normal and pathologic values is a DD level of 500 ng/mL [1,3]. In addition, if DD level is greater than 1600 ng/mL, it may also rule in AoD [3]. The number of published articles focusing on DD in PubMed is high: 6913 from 1975 until now, out of which 611 in 2013
☆ This work has been supported by the Serbian Ministry of Education and Science (Belgrade, Serbia), grant no. III41018.
1427
(search performed on 8/12/2014). However, the difficulty in assessing and comparing the results of these studies is the fact that, to date, at least 10 different numerical units have been used to express DD results. Before 2013, at least 9 different numerical units were used for DD in medical literature [4]. During 2013, the number was also 9 (PubMed search performed on 8/12/2014, too): milligrams per deciliter [5], milligrams per liter [6], micrograms per milliliter [7], micrograms per deciliter [8], micrograms per liter [3], nanograms per milliliter [9], nanograms per deciliter [10], nanograms per liter [11], and picograms per milliliter [12]. Moreover, 1 additional numerical unit appeared in 2014: milligrams per milliliter [13]. Taken together, during the last 18 months alone, at least 10 different DD units (DDUs) have been used in medical publications. In addition, number of units may actually be twice as high (even 20) because DD can be reported in 2 different measurement types: DDU or fibrinogen equivalent units, with 1 DDU being equivalent to 2 fibrinogen equivalent units [14]. We therefore suggest that the preferable unit for DD should be either nanograms per milliliter or the equivalent micrograms per liter because of the following: (1) The normal concentration can be expressed as the whole positive number (230 ng/mL seems better than 0.230 μg/mL, although both reflect the same concentration); (2) Upper normal limit suggested by the international guidelines for PTE and AoD is 500 in ng/mL [1] and 500 μg/L [3]; (3) Age-adjusted cut-off for PTE/venous thromboembolism was suggested to be calculated as: number of patients' years × 10 (in micrograms per liter) [15]; and (4) Approximately 51% of the publications (available in PubMed) express the results as nanograms per milliliter. PubMed search, performed on August 12, 2014, resulted in the following number of publications with different numerical DDUs: milligrams per deciliter was used in 107 publications, milligrams per liter in 201, micrograms per milliliter in 85, micrograms per deciliter in 2, micrograms per liter in 44, nanograms per milliliter in 573, nanograms per deciliter in 16, nanograms per liter in 26, and picograms per milliliter in 71. To conclude, no less than 10 various units have been used for DD in the last 18 months. We suggest the preferable unit for DD should be (the most commonly used) nanograms per milliliter, but there is even more suitable unit: micrograms per liter because the values expressed in nanograms per milliliter and micrograms per liter are numerically equal, and the second one is directly in liter, not derived unit. The standardization of the DDUs is essential in achieving easy and accurate interpretation and more importantly comparison of DD results. We can afford ourselves the unification of DDUs at no cost. Acknowledgment The author thank Associate Professor Vera Ignjatovic PhD, BSc (Hons), cogroup leader, Haematology Research, Murdoch Childrens Research Institute; principal fellow, Department of Paediatrics, The University of Melbourne, Australia, for the scientific edit of the manuscript. Goran P. Koracevic, MD, PhD Department of Cardiology, Clinical Center and Medical Faculty University of Nis, Nis, Serbia E-mail address: [email protected] http://dx.doi.org/10.1016/j.ajem.2014.08.042 References [1] Torbicki A, Perrier A, Konstantinides S, Agnelli G, Galiè N, Pruszczyk P, et al. Task Force for the Diagnosis and Management of Acute Pulmonary Embolism of the European Society of Cardiology. Guidelines on the diagnosis and management of acute pulmonary
