Not necessarily, any GP can test for hidden blood in stool though. Black stool is indicative of a bleed higher up in the GI tract anything bright and Tim’s likely hamprrhoids.

(And on the reverse black or blood coloured vomit)

You need to talk to your physician though, daily naproxen might be the best treatment option even with all the risks, But there‘s also other treatment options for arthritis, especially if you are using OTC painkillers daily.