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Medical Intensive Care Unit; Soroka University Medical Center; Beer-Sheva 84101, Israel; almogya{at}bgumail.bgu.ac.il
In Response:
We appreciate the interest of Drs. Lucas and Wians (1) in our work and would like to address the various issues expressed in their letter.
First, as stated in the Methods section, patients with acute myocardial infarction were excluded as per our protocol (2). According to the ACC/AHA guidelines an elevated troponin level is insufficient by itself to establish a diagnosis of myocardial infarction, unless accompanied by typical symptoms, a ST segment shift, new Q waves or coronary intervention (3). We did exclude patients who fulfilled criteria for new myocardial infarction. It is well established that reasons other than thrombotic myocardial infarction can cause elevated serum levels of cardiac troponins (4,5). Such elevation has been described in severe sepsis, pulmonary thromboembolism, and a wide variety of additional conditions. To what extent does troponin elevation in critically ill patients reflect a thrombotic ACS is obviously a different question. It is clear that elevated troponin levels alone are unable to differentiate between thrombotic and nonthrombotic etiologies. To our knowledge, only one study attempted to address this question, on which we had the privilege of providing an editorial comment (6,7).
Second, we apologize for the inaccuracy in the description of the CTnT assay. The assay was the Roche CTnT assay (the only one commercially available). A level >0.03 ng/mL was indeed considered abnormal based on a study of a healthy population in our laboratory that established a coefficient of variation <10% above this cut-off value.
Third, we believe that from the conceptual standpoint as opposed to the linguistic one, our cohort was indeed nonselected to the extent relevant to our study namely, the prognostic value of NT-pro-BNP in critically ill medical patients. We excluded only patients with conditions known to cause NT-pro-BNP elevation. Other than that no additional selection criteria were used. Specifically, no discrimination was made between patients with and without sepsis.
Fourth, we agree that the sentence describing NT-pro-BNP sampling might have been somewhat better phrased. However, no ambiguity should arise concerning the protocol or methods used.
Finally we agree that the limitations perspective and context of our study were extensively discussed.
REFERENCES
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