It started as a joke and ended with a bit of news that one guy hadn't bargained for.

In 2015, after taking a male pregnancy test and discovering he was apparently expecting, a man took to the online community Reddit and shared a digital comic poking fun of his discovery, when it should have first been alarming.

But more than 1,500 of his fellow Redditors saw past the humor and actually left concerned comments. What did they know about the erroneous results that he didn't?

A positive male pregnancy test is actually a scary thing for a guy.

No, you're not pregnant, it just means that there is something more sinister going on that you need to get checked out immediately.

Now, peeing on a stick can be nerve-wracking for both sexes because it can indicate pregnancy for women, and cancer for men.

A Reddit user, CappnPoopdeck, posted a “rage comic” that depicted a man who, as a joke, took an unused pregnancy test left behind by his ex-girlfriend. Weirdly, the test came back positive.

The test result was no laughing matter to other Redditors. They were quick to warn him that the positive pregnancy test result could be a sign of testicular cancer.

“If this is true, you should check yourself for testicular cancer. Seriously. Google it,” reads one of over 1,500 comments on the post. Better yet, he should have immediately scheduled an appointment with his doctor.

But how do pregnancy tests work and what do they screen for?

Pregnancy tests work by determining levels of beta-human chorionic gonadotropin (hCG) in urine. This indicates whether a woman is pregnant or not.

But “it turns out a fair number of testicular cancers make the same exact hormone,” oncologist Dr Mark Pomerantz said.

“There are very few things in the body that produce beta hCG, and testicular cancer is one of them.”

CappnPoopdeck posted an update in the form of another comic. The second comic said that the man who took the pregnancy test was an unidentified friend.

His friend reportedly visited doctors who found a small tumor in the man’s right testicle.

The tumor was luckily caught very early, but the friend most likely lost the testicle, according to the update. But because he took the pregnancy test, he was alerted to his testicular cancer early, and, as with all cancers, it's best to catch it in the beginning stages.

Dr Christopher Wood, chairman of urology at the University of Texas MD Anderson Canceter Center said that a painless lump is usually the first sign of testicular cancer, and he recommends that men conduct monthly elf-examinations.