It’s a little ironic that February has been designated American Heart Month – we’ve chosen the shortest month of the year to bring attention to the leading cause of death in this country. But with hearts in every store window for Valentine’s Day, it makes sense to spend some time in February reflecting on heart health and the devastating impact of heart disease.
Laboratory testing has been incredibly important in improving diagnosis of heart disease, particularly acute myocardial infarction (MI), or heart attacks. Stress to the heart muscle, caused by loss of blood flow, can damage cardiac cells. Dying cells release intracellular enzymes and other biomarkers of injury, and serum levels of these biomarkers follow a reliable pattern of rising and falling after an infarct event. Troponin and CK-MB are most commonly tested for, and troponin assays in particular have been evolving to more and more sensitive methods, able to detect smaller and smaller rises. Thanks to these advances in laboratory testing, emergency physicians are able to diagnose heart attacks faster and more reliably even when they’re mild. Small heart attacks are a warning sign for deadly ones later on, so a fast and accurate diagnosis leaves time for interventions than can prevent a future fatal attack. This is especially important for women.
Statistically, women are less likely than men to survive their first heart attack. This is due in part to the difference in symptoms between the two sexes. The stereotypical chest pain radiating down the left arm is more common in men who are experiencing a cardiac event. For many women, heart attacks come with vague and nonspecific symptoms like nausea, shortness of breath, fatigue, and back pain.
Could we be doing better for women’s heart health, and diagnosing small heart attacks early enough to intervene and prevent future damage? With so much of the diagnosis depending on laboratory test results, what role can the lab play in improving cardiac event outcomes? There’s some evidence to support changing the laboratory critical value cutoff for troponin in order to catch more of these silent heart attacks in women.
A study reported in the British Medical Journal in 2015 found that the 99th percentile of serum troponin, usually used as the indicator for acute myocardial infarct, is lower in women compared to men. When a lower threshold was applied to female patients presenting with cardiac symptoms, the results suggested that using sex-specific troponin thresholds could help to identify more women at increased risk of recurrent cardiac events.
Medicine isn’t one-size-fits all, and as assay sensitivity improves we’re learning that the same can be said for lab testing. A better understanding of where to draw the lines for accurate diagnosis can help health care providers to identify at-risk patients earlier, and intervene to save lives.