A POPULAR online community has helped a man discover a testicular tumour after he joked about a positive result on his girlfriend's pregnancy test.

The man drew more than 1000 comments on Reddit when he submitted a web comic illustrating his funny experience of testing positive when he took an unused pregnancy stick for a spin.

He was obviously alarmed when the test returned a positive result - indicated by two pink lines - joking that he was shocked to learn he was a pregnant man.

But one keen-eyed reader alerted him to the very real and serious possibility that the result was in fact no joke.

"You may have testicular cancer! Get to an oncologist, tell them you took a pregnancy test and it came out positive," one person wrote.

The man took his advice and his doctor discovered a small tumour on the man's right testicle.

Apparently some testicular cancers produce the same hormone, beta hCG, tested for by pregnancy kits.