Lab Tests Don’t Make Diagnoses, Doctors Do
Article Outline
During the last 10 years, I have been involved in a process that sought to create a clinical definition of myocardial infarction that could and would be used universally by clinicians and clinical investigators throughout the world. The impetus for this task was the observation that clinicians in different hospitals, and even within the same hospital, were employing different criteria to identify and categorize patients with acute and/or healed myocardial infarction. The confusion that resulted from these differing definitions of myocardial infarction is obvious. Moreover, different clinical trials involving therapeutic interventions for patients with myocardial infarction were defining the disease differently, thus making it difficult to compare results from one trial with those from another investigation since the patient populations studied differed in the 2 trials.
The first American College of Cardiology/European Society of Cardiology task force published its recommendation for a universal definition of myocardial infarction in 2000.1, 2 This new definition was based on measurement of the highly sensitive and specific biomarker of myocardial necrosis, troponin. This first attempt at creating a universal definition of myocardial infarction was largely successful, with cardiologists around the world adopting the new criteria. Unfortunately, the new definition also proved problematic for some physicians because abnormal blood troponin levels can and do occur as a result of any process capable of injuring myocardium. For example, myocardial injury as defined by elevated blood troponin values can be observed in patients with perimyocarditis, cardiac trauma including micro trauma associated with cardiac surgery, intracardiac electrophysiological ablation procedures, massive pulmonary embolism, and in critically ill patients whose course is complicated by sepsis, hypotension, and/or hypoxemia. Some clinicians labeled these latter patients as having had a myocardial infarction based on the new universal definition.
The initial task force to define myocardial infarction was well aware of the potential for confusion that might occur in patients with elevated blood troponin levels resulting from a process other than ischemic heart disease. The first report from the task force to create a universal definition for myocardial infarction emphasized the fact that multiple factors could injure myocardium thereby resulting in abnormal blood troponin levels. Despite this warning, many clinicians remained uncertain of the diagnosis when confronted with a patient who demonstrated abnormal blood troponin levels in a setting that was not suggestive of myocardial ischemia, for example, cardiac trauma. A careful reading of the first report on the definition of myocardial infarction reveals clearly that myocardial infarction should be diagnosed when elevated blood troponin levels are observed in a clinical setting that suggests myocardial ischemia, such as chest discomfort with the quality and duration of ischemic heart pain or when electrocardiographic (ECG) changes suggestive of myocardial ischemia are noted. Unfortunately in some settings, the clinical and ECG components of the task force definition were often overlooked, and patients received a diagnosis of myocardial infarction based solely on an elevated blood troponin level.
Because of inappropriate and inaccurate interpretation of abnormal blood troponin levels in clinical settings not suggestive of myocardial ischemia, many clinicians came to disparage the use of blood troponin levels for making a clinical diagnosis of myocardial infarction. These physicians claimed that the troponin test was “not specific enough leading to too many false positive results.” The fault here lay not with the troponin assay but with the clinical reasoning of the physicians involved. These individuals were basing their diagnosis of myocardial infarction solely on a laboratory test, often a single abnormal troponin value. These physicians failed to integrate the clinical history and ECG findings with the laboratory troponin values observed. This failure of basic clinical reasoning is something that I like to call “laboratory shortsightedness,” since the physician makes a diagnosis based solely on the laboratory variable measured and fails to integrate the laboratory findings with the complete clinical picture. A comparable mistake would be a diagnosis of hepatitis based solely on an observed abnormal blood liver function test. It is obvious that many processes can lead to abnormal liver function tests; hepatitis is just one of these entities.
A specific example of such an error in diagnosis secondary to misinterpretation of an abnormal laboratory test follows. The erroneous diagnosis detailed in this clinical scenario and the subsequent problems that it created for the patient are a good example of the harm that can result when abnormal laboratory tests are not interpreted in light of the full clinical history. A 32-year-old woman was admitted for a routine gynecological procedure. During induction of anesthesia, the patient developed an unusual reaction to the anesthetic employed. Her systemic blood pressure fell to an undetectable level and cardiopulmonary resuscitation was initiated. After 5 minutes of intensive intravenous pressor support, normal systemic blood pressure was restored. Following this untoward event, the patient was monitored for several days in the surgical intensive care unit. Her ECG briefly demonstrated transient shallow T wave inversions in the precordial leads following the event. Troponin blood levels were moderately elevated at 12 and 24 hours following the episode of hypotension. On the third day after the hypotensive episode, a cardiac catheterization, including coronary arteriography, was entirely normal. In her discharge summary, signed by an attending physician, one of the diagnoses listed was “acute myocardial infarction.” Several years later, the patient was denied life insurance because of her prior “infarction.” Multiple physician letters and phone conversations with the insurance company were required before the patient was eventually granted life insurance. The company physician eventually agreed that, indeed, this patient had suffered a myocardial injury secondary to an untoward reaction to anesthesia and that this was not an “acute myocardial infarction.”
Recently, a task force composed of representatives from the European Society of Cardiology, the American College of Cardiology, the American Heart Association, the World Heart Federation, and the World Health Organization produced a document that revised the original attempt at a universal definition of myocardial infarction from 2000.3, 4, 5 Much new scientific information has been reported since the publication of the original definition. The current revision document includes material reflecting the scientific advances of the last 7 years. Nevertheless, an elevated blood troponin level in an appropriate clinical setting involving symptoms and/or ECG changes suggestive of ischemia is still the “gold standard” for defining an acute myocardial infarction. Healed infarcts, of course, cannot be diagnosed by means of abnormal blood troponin measurements since these values will have returned to normal during the healing phase of the myocardial infarction. Thus, the diagnosis of a healed myocardial infarction depends on ECG and/or imaging criteria. The patient might even have forgotten or denied the symptoms that occurred at the time of the acute infarction.
The take-home message from this editorial is as follows: a laboratory test by itself rarely, if ever, establishes a clinical diagnosis. Careful collection of other clinical information such as history, physical findings, and associated diagnostic studies (for example, ECG or imaging) are almost always required in combination with laboratory tests such as blood troponin levels in order to establish a rational and reproducible clinical diagnosis.
References
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- Myocardial infarction redefined—a consensus document of the Joint European Society of Cardiology/American College of Cardiology/Committee for the redefinition of myocardial infarction. J Am Coll Cardiol. 2000;36:959–969
- . Joint ESC/ACCF/AHA/WHF Task Force for the Redefinition of Myocardial Infarction (Universal definition of myocardial infarction). Eur Heart J. 2007;28:2525–2538
- . Joint ESC/ACCF/AHA/WHF Task Force for the Redefinition of Myocardial Infarction (Universal definition of myocardial infarction). Circulation. 2007;116:2634–2653
- . Joint ESC/ACCF/AHA/WHF Task Force for the Redefinition of Myocardial Infarction (Universal definition of myocardial infarction). J Am Coll Cardiol. 2007;50:2173–2195
PII: S0002-9343(07)01083-2
doi:10.1016/j.amjmed.2007.10.015
© 2008 Elsevier Inc. All rights reserved.
