When a test isn't a test

There are many reasons why we request tests, in medicine. One imaginary patient's journey picks up a number of them.

Take a patient who presents with a painless lump on their arm, who's tired and a bit pale and washed out. You might send a series of blood tests, including a full blood count to diagnose anaemia. You may also request an ultrasound of the lump, which may show an ugly mass with features consistent with sarcoma. Your …