A song written and performed by the Mashed Potato Man about the perils of requesting a d-dimer in the emergency department I saw a woman in ED and she said she's breathless Her peak flow is low, her chest is full of a wheeze She's clearly asthmatic So why did they ever consider she might have PEs Why, Why, Why D-dimer Why, Why, Why D-dimer Can't you see its low specificity Means you get a false positive and a pointless CT I saw a man with cancer and he said he's breathless He took to his bed then suddenly collapsed to the floor It's clearly an embolus With a false negative d-dimer I had to ignore Why, Why, Why D-dimer Why, Why, Why D-dimer I implore of you see someone breathless just pause Don't send a d-dimer with an obvious alternative cause And remember to work out your pretest probability score.