Introduction to diagnostic tests part 1

Podcast – Diagnosis in Emergency Medicine Part 1 – SpIN and SnOUT

At the heart of emergency medicine is the fundamental question patients ask: “Doctor, what’s wrong with me?” Our goal is to answer this through meticulous history-taking, thorough examinations, and appropriate tests. But what does making a diagnosis truly mean?

This post is part 1 of a series looking at diagnosis in the Emergency Department.

Listening Time – 22:37

Mastering Diagnostic Uncertainty in Emergency Medicine

Welcome to the St Emlyn’s podcast, where we delve into the core of emergency medicine. I’m Iain Beardsell, and alongside Simon Carley, we aim to unravel the complexities of diagnostic uncertainty that we face daily in the emergency department (ED). Today, we’ll explore what it means to diagnose, the importance of ruling out life-threatening conditions, and how we balance certainty with the inherent risks of misdiagnosis.

The Heart of Emergency Medicine: Diagnosis

In day-to-day practice, diagnosing often involves applying a label to a patient’s condition. We either confirm a specific condition and decide on a course of action or, more commonly in emergency medicine, rule out severe conditions. This process enables us to reassure patients and, if safe, discharge them.

Ruling Out Serious Conditions First

Our diagnostic approach often works backwards. Instead of initially pinpointing what is wrong, we start by ruling out serious, life-threatening conditions. This method is particularly crucial in emergency medicine, where we prioritize identifying issues that could be fatal within hours.

We rely heavily on tests with high sensitivity to rule out these severe conditions. Sensitive tests are designed to identify all potential cases of a disease, ensuring minimal false negatives. While blood tests and imaging are common, the most powerful diagnostic tools we have are often clinical history and physical examination.

Understanding Sensitivity and Specificity

Two critical concepts in diagnostic testing are sensitivity and specificity. Sensitivity (SnNout) refers to a test’s ability to correctly identify those with the disease (true positives) and is key in ruling out conditions. Specificity (SpPin), on the other hand, measures a test’s ability to correctly identify those without the disease (true negatives) and is crucial for confirming a diagnosis.

For example, a highly sensitive test for pulmonary embolism (PE) ensures that almost everyone with the condition is identified. However, even a 98% sensitivity rate means that 2% of cases could be missed, which translates to one in 50 patients.

Balancing Certainty and Risk

We can never be 100% certain in diagnosis, and the expectation of infallibility can be problematic. Patients and some medical publications might assume that we should never make mistakes, but the reality is that high sensitivity tests still miss some cases. This uncertainty must be communicated clearly to patients, emphasizing the importance of returning if symptoms persist or worsen.

The concept of probabilistic diagnosis is essential. When we label a condition, we recognize that our patient population is a mix of true positives (those who genuinely have the condition) and false positives (those who do not but test positive). Similarly, those who test negative include both true negatives and some false negatives. Understanding this helps us make more informed decisions about further testing and treatment.

When to Stop Testing

Determining when to stop testing is critical. Over-testing can lead to unnecessary procedures, discomfort, and even harm. For instance, using less invasive methods like D-dimer tests for DVT (deep vein thrombosis) can avoid more invasive and risky procedures like venography. We reach a balance point where the risks of further testing outweigh the benefits.

The burden of disease plays a role here. Minor cases might be missed without significant consequences, whereas missing a major condition like a subarachnoid hemorrhage could be catastrophic. Therefore, our threshold for certainty varies with the severity of the potential condition.

Positive Diagnoses and Treatment Implications

When we make a positive diagnosis, we must consider the consequences of treatment. For example, diagnosing myocardial infarction (MI) leads to significant interventions like thrombolysis or PCI, which carry risks such as bleeding. Thus, we need a high level of certainty before proceeding with such treatments.

In emergency medicine, many of our decisions, like performing a thoracostomy in trauma patients, are based on rapid assessments often made in suboptimal conditions. These decisions highlight the importance of balancing clinical judgment with diagnostic test results.

Favourite Diagnostic Tests

To wrap up, we shared our favourite diagnostic tests. Ian prefers the ultrasound machine in the resus room, particularly for identifying pneumothorax in trauma patients. It’s immediate, actionable, and highly effective. Simon, however, has a soft spot for D-dimer tests, not because they are perfect, but because they illustrate the importance of understanding how diagnostic tests work and are often misunderstood or misused.


Emergency medicine thrives on the ability to navigate diagnostic uncertainty. By focusing on ruling out life-threatening conditions first, understanding the nuances of sensitivity and specificity, and balancing the risks and benefits of further testing and treatment, we strive to provide the best care for our patients.

We hope this exploration helps you reflect on your practice and enhances your understanding of diagnostic processes in the ED. Stay tuned for part two, where we will delve deeper into making decisions and diagnoses in emergency medicine.

Remember, while diagnostic tests are invaluable, nothing replaces the power of a good history and physical examination. Until next time, take care and keep questioning to improve your practice

Podcast Transcription

Where to listen

You can listen to our podcast in numerous ways, ensuring you never miss an episode no matter where you are or what device you’re using. For the traditionalists, Apple Podcasts and Google Podcasts offer easy access with seamless integration across all your Apple or Android devices. Spotify and Amazon Music are perfect for those who like to mix their tunes with their talks, providing a rich listening experience. If you prefer a more curated approach, platforms like Podchaser and TuneIn specialize in personalising content to your tastes. For those on the go, Overcast and Pocket Casts offer mobile-friendly features that enhance audio quality and manage playlists effortlessly. Lastly, don’t overlook YouTube for those who appreciate a visual element with their audio content. Choose any of these platforms and enjoy our podcast in a way that suits you best!

Cite this article as: Iain Beardsell, "Podcast – Diagnosis in Emergency Medicine Part 1 – SpIN and SnOUT," in St.Emlyn's, June 10, 2014,

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