Feb 28, 2017
Katrin Hruska discusses the usefulness of biomarkers in Emergency Medicine.
All biomarkers are awesome predictors of badness. Elevated hS-troponins after non-cardiac surgery or an acute exacerbation of COPD are associated with increased mortality.
In seemingly healthy people, elevated D-dimer levels are associated with increased mortality. Similarly, NT-proBNP levels predict mortality in patients with end-stage renal disease.
A biomarker, in its broadest sense, is defined as “a characteristic that is objectively measured and evaluated as an indicator of normal biological processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention” (NIH Biomarkers Definitions Working group, 2001).
This definition includes everything from laboratory tests to blood pressure measurements or an ultrasound scan. The clinical assessment in the Emergency Department is based on the subjective history of the patient and all available biomarkers (and their change over time).
If we assume that biomarkers are objectively measured, there is an overestimation of their individual importance.
In a clinical context the ease of getting a laboratory test leads to a lower threshold for testing. This increases testing without affecting relevant clinical endpoints. Also, when a biomarker becomes part of the standardised workup for a certain symptom, primary care centres and emergency telephone services will refer patients to the Emergency Department for testing, even when the pretest probability is low.
Katrin contends this bias is not an inherent problem of biomarkers themselves, but of the decision-making process of clinicians. The human brain fears uncertainty. Anything that adds to the feeling of knowing is rewarding, which is the most probable explanation of over testing in settings where medico-legal risks for the clinicians are low.
There is an ever-increasing number of patients seeking to rule out serious conditions by relying on biomarker testing to provide certainty.
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