What turned this patient's stool silver?

An elderly patient presented to ED with a two-week history of dizziness and 'unusually coloured stool'

It’s not unusual for stool to come out in a range of colours other than brown.

Yellow could indicate coeliac disease, whereas red is suggestive of cancer or colitis.

But doctors in the US received a shock when they treated a woman whose faeces were a shade missing from the standard stool colour chart — a metallic silver.