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 223 - July and August 2023 Monthly Round Up
Ep 222 - Monthly Round Up June 2023 - Airways, AMAX4, Head Injuries, TXA and more
Ep 221 - Brief Resolved Unexplained Events with Jilly Boden at the PREMIER Conference
Ep 220 - Penetrating Injuries with John O’Neil at the PREMIER Conference
Ep 219 - Blast Injuries with Chris Hillman at the PREMIER Conference
Ep 218 - Non epileptiform seziures with Steve Warriner at the PREMIER Conference
Ep 217 - Weaning the wheezy child with David James at the PREMIER Conference
Ep 216 - April 2023 Monthly Round Up: HALO procedures and Blood Transfusion
Ep 215 - March 2023 Monthly Round Up
Ep 214 - Shock from St Emlyn’s Medical School
Ep 212 - February 2023 Monthly Round Up
Ep 211 - Semi structured interviews (CAN 9)
Ep 210 - January 2023 Monthly Round Up
Ep 209 - November and December 2022 Round Up
Ep 208 - What is Wellbeing with Liz Crowe
Ep 207 - Burnout with Liz Crowe
Ep 206 - October 2022 Round Up
Ep 205 - September 2022 Round Up
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