I teach doctors how to interpret test results—and the labels 'normal' and 'abnormal' often hide what matters most
V felt tightness across his chest. His deepest breaths felt shallow. He sought help at an emergency department, where a resident physician found several worrying signs, including swelling of his hands and legs as well as heart enlargement on a chest X-ray.
V faced chest tightness and shallow breathing, leading him to seek emergency medical care. Upon examination, several warning signs were observed, yet the diagnosis of heart failure was initially suggested based on swelling and heart enlargement on a chest X-ray. However, the blood test for BNP, a hormone released by the heart under strain, came back normal, raising doubts about the diagnosis.
The resident physician knew that BNP levels could be abnormally normal in obese patients, even with heart failure. He therefore opted to administer a diuretic, a common treatment for heart failure, to help V eliminate excess fluid. Despite this, V's condition did not improve. A colleague, supervising the medical team, discovered the overlooked diagnosis of cardiac tamponade through an ultrasound.
This life-threatening condition occurs when fluid accumulates in the sac surrounding the heart, compressing it and hindering its ability to pump blood effectively. The diuretic could have potentially been fatal, but V was fortunate to be rushed to surgery and have the fluid drained, saving his life. This incident raises questions about the interpretation of test results, particularly the simplistic use of labels like "normal" and "abnormal."
Doctors generally consider BNP values under 100 pg/mL to be normal, but patients with excess weight and heart failure often have BNP levels below 100, albeit not by much. A BNP value under 50 is uncommon in heart failure, even in overweight patients. In V's case, the BNP level was 14, which was not just normal but exceptionally low, strongly contradicting the diagnosis of heart failure.
The labeling of "normal" conceals crucial information that could guide doctors towards alternative explanations. Doctors are often trained to rely on these simple labels, despite the nuanced insights they can provide. The 21st Century Cures Act, enacted in 2016, has enhanced patients' access to their health data, but this transparency comes with a hidden cost.
Patients may receive false alarms from "abnormal" results and false reassurance from "normal" ones. As a physician who teaches diagnostic test interpretation, the author wonders why some clinicians settle for a simple "normal" or "abnormal" reading rather than considering the full range of possible values. For instance, D-dimer test results between 500 and 1,000 ng/mL can slightly decrease the likelihood of a blood clot in low-risk patients.
Similarly, LDL cholesterol levels usually below 100 mg/dL are considered normal, but for heart attack or stroke survivors, anything above 55 is considered too high. The author emphasizes that the exact numerical value of a test result offers doctors far more insight than the mere labels of "normal" or "abnormal" can provide. By providing patients with a more detailed understanding of their test results, a conversation can ensue, leading to more informed medical decisions.
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