Like many people, Barbara Greenberg wasn’t looking to unlock any deep, dark family secrets when she spit into a tube a few years ago and sent her DNA off to be analyzed. “I was just curious to see if I would find anything a bit interesting,” Greenberg says.

And at first, there were no real surprises; she was, as expected, 100 percent Eastern European Jewish. But she’d check back into her account now and then, looking for new matches to distant cousins, and eventually someone else popped up—an unknown female relative with a DNA match significant enough to indicate it was likely a half-sister.

As Greenberg and the other woman began communicating, their shared story took shape. Although the other woman had very little information about who her biological father might have been, Greenberg says the timing, location, and certain clues the woman’s mother had given over the years indicated that they did, indeed, share the same father.

“Then I started getting panicky emails from her,” Greenberg says. “She said she spoke to her mother and her mother said it isn’t possible she was ever with a Jewish man, and she thinks it’s unlikely we’re related.”

And just like that, Greenberg lost the half-sister she never knew she had.

“I’m really frustrated,” says Greenberg, a child and family psychologist in Connecticut. “I’m a curious person who loves people’s life stories. I get to hear people’s stories as part of my job and now part of my own story is so frustrating; I have this half-sister who is disgusted to be related to me.”

Greenberg’s case is certainly not an isolated incident. As millions flock to companies like Ancestry, 23andMe, MyHeritage, FamilyTreeDNA and LivingDNA, the dust is getting blown off a wide array of long-buried family secrets, from adoptions to affairs to artificial insemination with donor sperm.

The latter is the topic of author Dani Shapiro’s latest memoir, Inheritance. Shapiro also took a mail-in DNA test—her husband was doing it; would she like one, too?—and discovered that she couldn’t possibly be her father’s biological daughter. Her experience inspired her to create the Family Secrets podcast, in which she interviews guests about how they discovered long-hidden family secrets.

These sorts of stories are echoed time and again in the news; perhaps among the most jarring is this case in which at least 50 half-siblings have been identified from the same sperm donor. And as the DNA databases continue to grow by the millions, more of these stories will be told. So if you’re not taking a test with the specific intent of locating a long-lost biological relative, you may want to pause a consider a few things before you start spitting.

Know your triggers

If you’ve got certain emotional triggers, such as around abandonment or being lied to, consider those before you take the test.

“I’m sensitive to feeling rejected; that’s a trigger for me,” Greenberg says. “In retrospect, I wish I hadn’t done it because it opened up a possibility, and then it opened up a rejection.”

If you know that finding out information you weren’t expecting might cause you mental distress, that may change your decision or at least allow you to consider the consequences and how you might cope with such a surprise ahead of time.

Take stock of who is still around

One of the most frustrating problems with the secrets being discovered through DNA testing is that quite often, anyone who might be able to explain what really happened is already dead. That’s the isolating experience Shapiro found herself in. She writes this in Inheritance:

I had scribbled down a very brief list of everyone I could think of—friends of my parents, elderly relatives, anyone at all who might still be alive, and could possibly know something, anything, about what happened in a fertility clinic in Philadelphia fifty-four years earlier. There were so few people left. My dad’s ninety-three-year-old sister, Shirley, was one, but I couldn’t possibly call her. If my father wasn’t my father, then she wasn’t my aunt.

The thought made me tremble, and I lowered myself into a plastic chair bolted to the floor. Grandparents, uncles, aunts, cousins floated away from me like dozens of life rafts.

As Shapiro discovered, it may also be possible that someone of that generation is still alive but either wouldn’t be willing to talk about it or may not know any more than you do. Consider how you might pursue the truth if you didn’t have anyone you could rely on for real answers.

Know that your shock may come later

When Greenberg initially got her results three years ago, there wasn’t much of anything interesting within them. It wasn’t until she logged back in years later that she saw the new close biological match that had appeared. Once one of these databases has your information, it stays there indefinitely.

That means even if nothing seems amiss now, it doesn’t mean you won’t find out something shocking five or ten years down the road. Consider whether you’re okay with that sort of thing looming in the background. You can choose an anonymous user name, indicate that you don’t want to be contacted by matches and vow to never again log in after viewing your initial results; but you may still find yourself tempted to check in from time to time.

Be prepared for disappointment

Disappointment can come in many forms with these results. It can be small (you get the exact mix of Eastern European heritage you’d always been told you had—even if you were hoping for a little something extra in the mix). Or it can be big (as we’ve already discussed).

But one disappointment you may have not considered is that if even you’re open to finding and meeting a few new relatives you previously knew nothing about, you might not always like who you get.

“You may find out you’re related to people that you don’t really care for or who aren’t that pleasant,” Greenberg says. “Be prepared for disappointment; even if you find biological relatives, they may not be people you would choose as friends.”

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