Blood Test May Soon End Heart Attack Uncertainty

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Roughly 5.5 million visits are made annually to emergency rooms as a result of chest pain. The worst-case scenario for any adult is a heart attack, and time is of the essence. Interventions must be performed rapidly.

In many cases patients who complain of chest pain, and it's not immediately apparent that they're having a heart attack, are admitted anyway until that possibility has been ruled out, at which time it becomes safe to discharge the patient. In today s culture of defensive medicine, let s just say that it's always better to be erring on the side of caution.

But now there's promising data from a study conducted in Scotland that could accurately rule out a heart attack -- with just one blood test.

It is called the high-sensitvity troponin assay. It's not yet available in the United States but doctors have begun using it in Europe. This is an exciting development as it has the potential to save billions of dollars in healthcare costs, cut down triage time and appropriate risk stratification in acute situations.

The study included 6,304 people admitted for suspected myocardial infarction (MI or heart attack). Patients were tested with both standard troponin lab test as well as the high sensitivity test. Less than five nanograms per liter of blood (one million nanograms is equal to one mg) accurately identified 61% of patients that were not having an acute heart attack.

What that translates to is that 99.6% of the time, researchers are able to accurately identify patients who are not having a heart attack. This is also known as the negative predictive value (NPV). Validation studies were consistent with these results.

The test becomes less reliable if people present within two hours of the onset of chest pain (NPV decreases to 97.6%). In these circumstances, repeating the blood test is advised.

Taking into account the patient s clinical picture with a blood test that's pretty accurate, physicians can feel much more confident about which patients warrant being admitted for further workup, and which can be safely discharged home with outpatient follow-up.

"This study shows us a novel way that the current generation of high-sensitivity, more accurate troponin assays could be used to improve the efficiency of chest-pain services without compromising safety, said Dr. William Parsonage, one of the study's authors.

When a patient presents with chest pain and is admitted, part of the subsequent workup involves serial monitoring of their troponin levels. Troponins are an indicator of heart muscle damage and a rising level signals that heart damage has occurred. Therefore, physicians monitor these levels to ensure that they do not rise over time.

Currently, three blood samples are needed eight hours apart to definitively say that a heart attack has not occurred.

It should be noted that this test cannot tell the clinician what the causal agent of cell damage was, therefore there is an increasing responsibility to interpret each test in clinical context, according to Matthew Sherwood, MD and L. Kristin Newby, MD in a review article for the American Heart Association.

A blood test should never absolve a clinician of looking at the whole picture. Careful consideration must be paid to the patient s clinical picture. However, the prospect of this test becoming available in the U.S. can have a significant clinical and financial impact in this area of medicine.