A man getting a positive result on a pregnancy test is no laughing matter, it turns out.


Reddit user CappnPoopdeck posted a comic last week joking about his 17-year-old friend's experience taking -- and testing positive on -- a pregnancy test left by an ex-girlfriend. But amid the ribbing comments, one user struck a serious tone.


“If this is true, you should check yourself for testicular cancer. Seriously,” Reddit user goxilo wrote.


Home pregnancy tests are designed to detect the hormone human chorionic gonadotropin, or hCG, which is produced by the developing placenta that will help nourish a fetus after conception. Rising levels of the hormone can be found in a woman's blood or urine, making it an ideal way to detect pregnancy. But the hormone is also put out by certain kinds of testicular tumors.


CappnPoopdeck's friend got tested soon after the Reddit post was made, and doctors found a very small tumor in his right testicle. One of the advantages of using hormone screenings to look for cancer is that elevated markers like hCG can alert doctors to tumors that are too small to be detected with other methods like computed tomography, or CT, scans.


In an update, CapnPoopdeck was conflicted, writing, “I'm sad he might lose a nut, while I'm also amazed a [pregnancy] test picked up a f---ing tumor and happy it was caught early, all at the same time.”


While most cases of testicular cancer require orchidectomy, or the removal of a testicle, one British study of 33 men with advanced germ cell tumors found that chemotherapy alone was enough to eradicate the cancer in 64 percent of the patients who had a certain kind of cancer called “pure seminomatous,” characterized by tumors with large round cells.


“It may not be necessary to undertake delayed orchidectomy in these patients,” the researchers wrote in the journal Clinical Oncology in April 2008.


Human chorionic gonadotropin is not the only molecule secreted by testicular tumors. Other common markers include alpha-fetoprotein, present in about 90 percent of testicular germ cell cancers, and lactate deyhdrogenase, an enzyme that can also be a sign of meningitis, human immunodeficiency virus, and acute pancreatitis if elevated levels are present.


Not all testicular and prostate tumors will secrete hCG, so a negative result on a pregnancy test for a man doesn't necessarily mean there's no cause for worry.


So, if you're growing a mustache for Movember to raise awareness about prostate and testicular cancers, remember to also check yourself regularly, with or without a pregnancy test.