The latest CAN is one of our brand-new 'revision editions' -- brief podcasts aimed at covering the essentials of critical appraisal for medical students and junior doctors preparing for exams.
With the help of Gregory Yates, an academic doctor based in Manchester, this episode introduces two core concepts: sensitivity and specificity. These are two ways of thinking about the accuracy of a diagnostic test. Knowing the sensitivity and specificity of an investigation will give you a decent idea of how it should be used in the emergency department.
Sensitivity (Sn) describes the chance that a test will be positive if your patient has the condition you're testing for. Some people call it the 'true positive rate' or alternatively the positivity in disease (PID) rate. If you need a hand remembering it, you can always remember that PID is a sensitive issue.
Meanwhile, specificity (Sp) considers the chance of a test being negative if the patient doesn't have the condition you're testing for. It's the 'true negative rate' or alternatively the negativity in health (NIH) rate. There are times when we particularly need a test to have a high sensitivity. This is generally when we want to be particularly confident that a test accurately identifies everyone with the relevant condition because we really don't want to miss it. We need a high sensitivity to rule out disease. (Sn-uff it out). At other times, we need to be confident that a patient with a positive test actually has the disease - for example, if the treatment is unpleasant or involves exposing patients to risk. In that case, we want a high specificity to rule in disease. (Sp-in it in).
In this CAN, we use D-Dimer as an example of a very sensitive investigation: it’s positive in nearly 100% of cases of venous thromboembolism. Specificity describes the likelihood that the test will be negative if your patient does not have the disease. We use HbA1c as an example of a highly specific investigation: it’s rarely used in the emergency department, but if it’s elevated, we can be almost certain that the patient is diabetic. HbA1c is almost never (
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Ep 128 - Can we use diagnostic probability to guide treatment thresholds in ACS with Charlie Reynard and Rick Body
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Ep 126 - December 2018 Round Up
Ep 125 - November 2018 Round Up
Ep 124 - Human factors, technology and humanity in critical care with Peter Brindley
Ep 123 - Five strategies to improve your resuscitations with Simon Carley at #stemlynsLIVE
Ep 122 - Beyond ALS with Salim Rezaie at #stemlynsLIVE
Ep 121 - October 2018 Round Up
Ep 120 - The pursuit of excellence with Nat May at #stemlynsLIVE
Ep 119 - September 2018 Round Up
Ep 118 - August 2018 Round Up
Ep 117 - EMS Gathering 2018 with Aiden Baron
Ep 116 - Moral Injury in emergency and prehospital care with Esther Murray
Ep 115 - July 2018 Round Up
Ep 114 - The past, present and future of IV Fluids in Paediatric Practice with Steve Playfor
Ep 113 - The best of badEMfest 2018
Ep 112 - Acute Psychiatric Emergencies in the ED.
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