The epic rise and fall of Theranos hasn’t put consumers or investors off the idea of finding a quick and easy way to learn from our blood.

The likes of Base, Thriva and Everlywell are now pushing the boundaries of personalized health care, using at-home blood tests to provide recommendations on the supplements we should take, the food we should eat, and how much exercise we should get. Between them, these companies have raised more than $350 million in venture capital cash, with the bulk of that made up by Everlywell’s recent $175 million funding round in December.

At-home blood tests join the growing ranks of other home tests for pregnancy, UTIs, and sperm. They serve as another method of bio-hacking as seen by the rise of continuous glucose monitoring devices, which also relies on a tapping your blood vessels.

Blood testing kits ask that users simply prick their fingers at home, and either fill up a test tube (in the case of Thriva) or splatter a card (as Base asks its customers to do) with droplets of blood. The samples are sent off in the mail, and a few days later a variety of charts and a few nuggets of lifestyle advice land in the donor’s inbox.

The promise of a personalized medical dashboard is compelling – but is the data these companies provide accurate, or is it all just a gimmick? We spoke to Dr. Harvey Kaufman, medical director at U.S. lab-testing giant Quest Diagnostics, for some insights.

What’s better for testing, a vial of liquid blood, or dry blood spots on a card?

When we compare [tests] like whole blood, plasma or serum, or dry blood, for many things they’re close, and generally for a lot of things close is good enough.

The advantage of dry blood spots is that they’re easily transported and they’re stable over a wide temperature range. But you have to have enough concentration [of blood] to detect what one wants. And there’s a little bit of variability compared to a traditional tube of blood, so they’re often more appropriate where we’re looking for more of an extreme value than a precise value.

When it comes to testing for, say, vitamin D and cholesterol levels, are both types of test adequate?

They’re adequate, but they’re not identical to a traditional laboratory test.

Just recognize that if we’re trying to differentiate a total cholesterol [level] of 180 versus 185, you’re not going to get that with a lot of the over-the-counter tests because they don’t have that precision. But if you’re looking for a 180 versus 200, or something more extreme, then yes, they are very good at that.

How do blood samples survive the mail?

Dry blood spots are fairly stable over a wide temperature range. [Liquid] blood specimens tend to have a narrower stability range. At Quest, we maintain specimen stability [using] three temperature boxes in every transport van (ambient, refrigerated and frozen) which allows us to ship specimens and maintain integrity. Some companies shipping blood will throw in a cool pack, but the issue with that is it adds weight and [therefore] cost.

Not all blood specimens are as stable as others – if you don’t properly handle the specimen, [the red blood cells can rupture], and then it’s easy to get elevated potassium values.

Are the results always accurate?

Every test has limitations, and you’ve got to understand the context in which the test has been [taken]. Doctors are pretty good at putting it all in context, but for the rest of us who are doing this sporadically, you’ve got to be a little bit concerned about over-interpretation or under-interpretation of results.

You mentioned vitamin D. Well, you don’t want to be taking vitamin D [supplements] in the morning and then testing an hour later. A few years ago I was having some routine blood work done and my hemoglobin A1c, which is a measure for diabetes diagnosis, had dropped – but I’d donated blood a couple of days earlier, [which was why].

Right. These aren’t the sorts of questions the at-home tests ask.

There’s a lot of caveats that doctors understand, and I think over time that is going to get embedded in the materials that we are presented before we purchase testing, and after [doing the] testing in terms of interpreting it in a fuller context.

What are some of the common mistakes people make when taking at-home blood tests?

In terms of finger stick [testing], you’re supposed to prick not directly in the middle of the finger tip, but to the side. You wipe away the first drop, and then you use the subsequent drops. As easy as that is to [explain], the reality is lots of people don’t do that.

For some people, it’s hard to get enough blood from a finger-prick test so they tend to squeeze the finger. That can lead to red cells bursting, and you can also get fluids that dilute the specimen. [With dry blood testing], sometimes there’s just not enough drops on the card, so you end up with inadequate specimens.

Most instructions today have graphics, which are great, [but] the written directions still tend to be at a level that’s higher than ideal for people to really understand. Honestly, home testing is never going to be foolproof because people do the darndest things.

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