Are we consistent in using 14 different units for brain natriuretic peptide instead of ng/L? Goran P. Koracevic MD, PhD PII: DOI: Reference:
S0735-6757(16)00041-3 doi: 10.1016/j.ajem.2016.01.031 YAJEM 55563
To appear in:
American Journal of Emergency Medicine
Received date: Accepted date:
16 January 2016 25 January 2016
Please cite this article as: Koracevic Goran P., Are we consistent in using 14 different units for brain natriuretic peptide instead of ng/L?, American Journal of Emergency Medicine (2016), doi: 10.1016/j.ajem.2016.01.031
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ACCEPTED MANUSCRIPT Are we consistent in using 14 different units for brain natriuretic peptide instead of
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ng/L?
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Fourteen various units for BNP
Goran P. Koracevic, MD, PhD
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Department of Cardiology, Clinical Centre and Medical Faculty, University of
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Nis, Nis, Serbia
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Goran Koracevic
+38118533644
fax number:
+38118238770
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telephone number:
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email address:
[email protected] mailing address: 9.brig. 53/50
18000 Nis,
Serbia
Acknowledgement: This work has been supported by the Serbian Ministry of Education and Science, grant No. III41018.
ACCEPTED MANUSCRIPT To the Editor,
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Natriuretic peptides (NPs), both B-type NP (BNP) and its precursor N-terminal Pro-BNP
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(NT-proBNP) are the most established acute heart failure (AHF) diagnostic biomarkers, being very useful in the emergency setting [1]. They improve diagnostic discrimination in
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patients with an undifferentiated dyspnea [1]. Moreover, BNP and NT-proBNP are currently believed to be useful in: excluding AHF [2,3]; diagnosing HF in primary care
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[4]; providing diagnosis of HF in patients with pleural effusion [5]; adding an
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incremental value for prognostication in chronic stable HF [6,7]; improving mortality prediction models in acute decompensated HF (ADHF) [8]; guiding therapy to decrease
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the risk of HF-related hospitalization but not of the risk of the all-cause mortality/hospitalization [9]; (The available evidence for BNP-guided HF therapy is of
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low quality, insufficient [10] and restricted to HF patients with the reduced left
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ventricular ejection fraction, as concluded in a meta-analysis) [11]; predicting postoperative atrial fibrillation (AF) after thoracic surgery [12] and following any surgery
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(cardiac or non-cardiac) [13]; predicting a new-onset AF in acute myocardial infarction (AMI) [14], and major adverse cardiac events following an AMI, etc.
NT-proBNP is also valid for the diagnosis and prognosis of ADHF in patients with renal dysfunction (with higher cut-off values as compared to patients without renal dysfunction) [15]. However, the prognostic utility of NT-proBNP can be overestimated in meta-analyses using study-specific optimal diagnostic thresholds, which are not equal and commonly not specified before study [16]. To summarize , NT-proBNP and BNP are very useful in contemporary (particularly emergency) medicine, as well as for scientific
ACCEPTED MANUSCRIPT purposes. For illustration, in PubMed, there have been a respectable number of 886
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papers about BNP that have been published in 2015 (search on 1/17/2016).
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It is important to update the knowledge about one of the most important cardiac biomarkers. This is hampered by the numerous BNP units used, which decrease the
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readability of the publications and make the comparisons difficult. There have been at least 14 different BNP units used: 1. mg/dl [17]; 2. µg/ml [18]; 3. µg/1000 µL [19]; 4.
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µg/L [20]; 5. ng/L [4,21,22]; 6. ng/ml [23]; 7. pg/L [24]; 8. pg/dl [25]; 9. pg/ml [26]; 10.
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fg/ml [27]; 11. nmol/L [28]; 12. pmol/L [29]; 13. pmol/ml [30] and 14. fmol/ml [31]. There is even a paper from 2015 in which no unit for BNP is written. Is the situation
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better with the NT-proBNP? For the NT-proBNP there is also no uniform unit, and at least six can be found in the medical literature: 1. ng/L [32]; 2. ng/mL [33]; 3. pg/dl [34];
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4. pg/ml [35]; 5. pmol/L [36] and 6. pmol/ml [37].
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To illustrate how different BNP units have been, let us compare µg/ml and ng/L, both
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used in recent papers [18,22]. As 1µg=1,000ng and 1ml=.001L, the numerical differences in measurement results can be as high as a million times. It is logical that ng/L should be the preferred unit for BNP, for at least 5 reasons: 1. litre (L) is a non-SI (The International System of Units) unit, accepted for use with the SI 2. L is the main unit, not a subunit; 3. results (including normal values) are in the range of whole numbers, not just decimals [4,21,22]; 4. ng/L is the second most commonly used BNP measurement unit, after pg/ml and the first two (ng/L and pg/ml) are numerically equal; and 5. measurement results of both BNP and NT-proBNP, can be expressed in the same unit (ng/L) [4] that
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proBNP.
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Together with the absolute unit ng/L, it is also prudent to include the additional relative unit for elevated BNP (and other biomarkers) - a number times the upper limit of normal
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(ULN), e.g., 7.5 times the ULN [38]. The correct addresses for the quest for unifying of BNP measurement units are the international societies of biochemistry and the companies
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producing analyzers for BNP and NT-proBNP, because clinicians and scientists tend to
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use the same measurement unit as the local laboratory. To conclude, no less than 14 different measurement units have been used for BNP, decreasing the readability and
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producing a unnecessary confusion. Efficacy matters in medical communication and
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knowledge exchange.
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