Diagnostic Testing In Emergency Medicine

by Yusuf Ali Altunci

 

Case 1

A fifty-one-year-old male patient is admitted to your emergency department (ED) with chest pain that started 30 minutes ago. On his ECG, there are 2 mm ST elevations at DII, DIII, and aVF derivations. Do you need high sensitive troponin analyzes results for acute management of this patient?

Case 2

A thirty-five year- old female patient presented to your ED with sudden onset shortness of breath. She has tachycardia. There is no pathologic finding at auscultation. Her blood pressure is 90/60 mmHg. In history, there is swelling and pain on her left leg for two days. She is using oral contraceptives. For this patient can normal D-dimer result rule out pulmonary embolism?

Introduction

The emergency physicians frequently make difficult clinical decisions with limited information while encountered with a multitude of demands and distractions (Kovacs & Croskerry 1999).

EDs are crowded places. Usually, you have limited time to diagnose and treat the patients. Today, diagnostic tools are better than they were in the past. This may help provide an easier diagnostic approach, but the difficulty is knowing how and when you should use these tools. Even if the technology has become available more frequently in clinical practice, clinical expertise and skills are still important factors for making correct, timely diagnoses in patients (Wahner-Roedler 2007).

So this triggers the question: is there one diagnostic approach for each emergency illness that can render the best result for the patient, maximize timeliness and accuracy, and limit cost? This is the essential question that clinical decision rules try to answer; therefore, the development of these reliable clinical decision rules is imperative for the advancement of modern emergency medicine (Pines 2012).

“Listen to your patient; he is telling you the diagnosis.” – William Osler (1849-1919)

Diagnostic Testing Approach

Polymorbid patients, different diagnostic and therapeutic options, more complex hospital structures, financial incentives, benchmarking, and perceptional and societal changes cause pressure on doctors, especially if medical errors come up. This is especially true for the ED structure, where patients encounter delayed or erroneous initial diagnostic or therapeutic actions and expensive hospital stays due to sub-optimal triage (Schuetza 2015)

Diagnostic tests should primarily be ordered to rule in or out a particular condition based on the differential diagnosis found through the patient’s history and physical examination (Wald 2011). For emergency management, it is usually more important to rule out life threating pathologies.

So why do we need diagnostic tests? For detecting the problem, of course; however, the decision to test is impacted by multiple factors such as clinical suspicion, persuasion, physician’s decision, consultant’s or patient’s request (Wald 2011).

Patients often express strong preferences for medical tests or treatments of their own choosing, even when physicians believe that those interventions are not beneficial (Brett & McCullough 2012). Patients are also increasingly willing to challenge physicians’ intellectual authority, often requesting interventions based on media publicity about new research findings, sometimes before physicians are even made aware of them. Internet sources with clinical information also empower patients to make medical judgments independent of consultations with physicians (Brett & McCullough 2012). The Internet continues to create new, unschooled Internet doctors and, in turn, new challenges.

Chosing the test or not test in the ED also depends on the resources of the hospital. Some hospitals allow easy access to radiographic testing and laboratory testing. In other hospitals, obtaining a diagnostic test may not be that simple (Pines 2012).

Questions for diagnostic strategy described by Wald (2011) are
• What am I going to do with the test results?
• How is this test going to help me confirm or exclude the diagnosis?
• How will the test result affect my diagnostic strategy, management, or final disposition?

“Medicine is a science of uncertainty and an art of probability.” – William Osler (1849-1919)

 

Statistics

You decided on one of the diagnostic tests for your patient. Do you think you should know some statistics in order to evaluate the results? Let’s check some basic statistical terms that we regularly face as a doctor.

Random ordering of laboratory tests and shortcomings in test performance and interpretation may cause diagnostic errors. Test results may be vague with false positive or false negative results and generate unnecessary harm and costs. Laboratory tests should only be demanded if results have clinical consequences (Schuetza 2015).

Sensitivity refers to the likelihood of a test being positive or abnormal in the presence of disease.

  • Sensitivity = True Positive/(True Positive + False Negative)

Specificity refers to the likelihood of the test being negative or normal in the absence of disease

  • Specificity = True Negative/(True Negative + False Positive)

A test that has high specificity means that it has a low rate of reporting false positives. A test that has low specificity has a high likelihood of false-positive results (Wald 2011).

Positive predictive value (PPV) refers to the likelihood of the patient truly having the disease when the test is positive or abnormal.

  • PPV = True Positive/(True Positive + False Positive)

Negative predictive value (NPV) refers to the likelihood that the patient does not have the disease when the test is negative or normal (Wald 2011).

  • NPV= True Negative/(True Negative + False Negative)

Probability

The other important element in testing is the probability. Previously, the physicians’ role in emergency medicine was clinical problem solving by history taking and examination only. Now it has changed and incorporates determining the pre- and post-test probabilities essential for the ordering and interpretation of laboratory tests (Schuetza 2015). Probability relates to your concern about a particular patient having an illness or condition and how that concern may or may not be impacted by the diagnostic test results (Wald 2011).

Testing-related diagnostic error

The EDs are often described as a diagnostic testing center where the results of most diagnostic tests are known within a few hours. The importance of diagnostic tests in Emergency Medicine is an undeniable fact. For example, there are a lot of diagnostic imaging alternatives available in the ED including USG, CT, and MRI in the ED. So, the pathologies that were mostly detected at autopsies in the past, such as pulmonary embolism or an aortic aneurysm, became a clinical problem for today (Wald 2011). Unfortunately, many “routine” laboratory tests are being ordered in “bundles” without any impact on diagnostic or therapeutic management (Schuetza 2015).

Five causes taxonomy of testing-related diagnostic error (Epner 2013)

  1. An inappropriate test is ordered.
  2. An appropriate test is not ordered.
  3. An appropriate test result is applied incorrectly.
  4. An appropriate test is ordered, but a delay occurs somewhere in the whole testing process.
  5. The result of an appropriately ordered test is not accurate.

Diagnostic Strategy

Diagnostics, including point of care testing in the ED, is still evolving. As our technology continues to improve, we will have greater access to the results of a multitude of diagnostic studies in a timely fashion (Wald 2011). It is our responsibility to practice medicine in a cost-effective manner that benefits our patients and does not overburden them and the health care system with unnecessary and, at times, overused testing (Wald 2011).

Blood circulating biomarkers play a crucial role in the present diagnostic workup of ED patients. A biomarker may be considered as any protein or other macromolecules that can be objectively measured and evaluated as an indicator of normal biological processes, pathological processes, and course of diseases or pharmacological responses to a therapeutic intervention. Readily measurable biomarkers give important information about etiology of a disease and the necessity for interventions and prognosis. Diagnostic biomarkers justify the presence or absence of a disease (Schuetza 2015).

In Emergency Medicine practice, we use algorithms or clinical decision rules (Ottawa Ankle Rules, PECARN minor head trauma algorithm, etc.) to make standard management. These are useful and practical tools to make an acceptable decision. Clinical decision rules try to make objective criteria that may help you to distinguish who requires a test or not (Pines 2012). Some people call it “cookbook” medicine, and, of course, “one size cannot fit all.” Today, however, they are the most evidence-based approaches to pathologies. So staying within the rules is one of the best methods that will assist you when contemplating when to utilize diagnostic tests.

Comprehending the evidence behind diagnostic testing and using clinical decision rules to decide when not to test is at the center of emergency medicine practice (Pines 2012).

Last questions that you should keep in mind:

  • Will that test result change your management?
  • Do you have any plan if it’s positive, negative, or indeterminate?

These questions should be considered before you order the test. It is our responsibility that giving the best, correct, and the fastest management to our patients. However, in the same time, it is our responsibility to use our resources wisely. Therefore, ordering the appropriate tests is very important. The tests which you think it will change your management and you know what are you going to do with the results are the best tests for your patients. In addition, this approach will help to use our resources efficiently and decrease the cost of of unnecessary tests.

References and Further Reading

  • Kovacs G, Croskerry P. Clinical decision making: an emergency medicine perspective. Acad Emerg Med. 1999;6(9):947-52.
  • Wahner-Roedler DL, Chaliki SS, Bauer BA, Bundrick JB, et al. Who makes the diagnosis? The role of clinical skills and diagnostic test results. J Eval Clin Pract. 2007;13(3):321–5.
  • Diagnostic Testing in Emergency Care.In: Pines JM, Carpenter CR, Raja AS, Schuur JD eds. Evidence-Based Emergency Care: Diagnostic Testing and Clinical Decision Rules 2nd ed. Wiley-Blackwell. 2012.29-36.
  • Schuetza P, Aujeskyb D, Muellerc C et al. Biomarker-guided personalized emergency medicine for all – hope for another hype? Swiss Med Wkly. 2015;145:w14079 .
  • Diagnostic Testing in the Emergency Department. In: Wald DA, editor. Emergency Medicine Clerkship Primer. A Manual for Medical Students. IL: Clerkship Directors in Emergency Medicine 2011:47-53.
  • Brett AS, McCullough LB. Addressing requests by patients for nonbeneficial interventions. JAMA. 2012;307(2):149-50.
  • Epner PL, Gans JE, Graber ML. When diagnostic testing leads to harm: a new outcomes-based approach for laboratory medicine. BMJ quality & safety. 2013;22(Suppl 2):ii6–ii10.
  • Pines JM, Carpenter CR, Raja AS, Schuur JD. Evidence-Based Emergency Care: Diagnostic Testing and Clinical Decision Rules 2nd ed. Wiley-Blackwell.

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