A drop of blood can tell you a lot about a person—whether he or she might have heart disease, an STD or diabetes, for instance, or tell-tale signs of certain cancers. But having blood drawn is somewhat of an arcane process, sometimes requiring nurses or phlebotomists to extract vials upon vials of blood. And when those vials are sent to a lab for testing, a lot can go awry. The vials can be misplaced, mishandled or simply misread; moreover, it can take days or even weeks for patients to learn the results.

To Elizabeth Holmes, an entrepreneur with a background in chemical and electrical engineering, waiting a week for such a crucial diagnostic procedure seems unacceptable. The delay could put the patient at serious risk s should his or her condition worsen without immediate interventions, such as taking medicines or seeing a specialist.

"The art of phlebotomy originated with bloodletting in 1400 B.C. and the modern clinical lab emerged in the 1960s—and it has not fundamentally evolved since then," Holmes tells the Wall Street Journal.

For a 21st-century society striving for technological efficiency, the arrival of Theranos, a blood test Holmes began developing a decade ago, has the feel of a long-overdue upgrade. Instead of putting a patient through what's known colloquially within the medical community as "blood work," Holmes says all she needs is a micro sample, equal in volume to a raindrop, to sufficiently run as many as 30 tests, the results of which can be available in less than a day.

Typically, blood samples undergo a somewhat complicated journey that involves first transporting them to a facility, where they are either mixed with chemicals or put through various pieces of equipment to be examined. It's during this transfer of liquids that up to 70 percent of errors occur, according to a report by the ECRI Institute, a heathcare nonprofit. Potential complications can arise if the sample's freshness isn't properly maintained during transit or while manually centrifuging samples to separate plasma and red and white blood cells. The risk of an error is compounded by the fact that labs use equipment from different vendors, which aren't always properly calibrated. Follow-up tests also tend to make the process even more time-consuming, error-prone and expensive.

The system that Holmes has perfected, however, is designed to run a wide range of tests, including follow-up assessments that can be completed in as little as a couple of hours. Rather than trucking samples to a lab, the Theranos testing is carried out on-site at either of its two current locations in California and Arizona—a decision, she says, that not only reduces the likelihood of mistakes, but also lowers costs.

Currently, her company aims to provide its services at half the price of Medicare and Medicaid reimbursement rates. For instance, cholesterol and HDL measurements, which normally cost about $30 out of pocket, cost $2.99. Customers can peruse the entire menu of blood tests, which are all be run from the same drop of blood, on Theranos' website. In a health care climate in which the cost of blood tests can vary wildly—illustrated recently through the story of one California woman who paid $4,000 for tests at one lab and $260 for the same tests at a lab down the street—Holmes hopes Theranos' menu can bring some transparency to the process.

So how does the technology work?

Though Holmes doesn't reveal any specifics about the proprietary method, she does say the approach is similar, in some ways, to conventional blood tests.

“We test for the same analytes,” she explains in an email. “The difference is in the size of the sample that is required. We also spent many years investing in infrastructure to be able to automate many of the processes that were traditionally error prone and overhead-intensive to produce our systems at a very low cost.”

Those who have taken the test haven't been privy to laboratory details, either, but some—including the Wall Street Journal's editorial writer Joseph Rago—have described the streamlined process they undergo in a clinical setting:

A Theranos technician first increases blood flow to your hand by applying a wrap similar to one of those skiing pocket warmers, then uses a fingerstick to draw a few droplets of blood from the capillaries at the end of your hand. The blood wicks into a tube in a cartridge that Ms. Holmes calls a "nanotainer," which holds microliters of a sample, or about the amount of a raindrop. The nanotainer is then run through the analyzers in a Theranos laboratory. Results are usually sent back to a physician, but a full blood work-up—metabolic and immune markers, cell count, etc.—was in my inbox by the time I walked out the door.

Most importantly, Holmes notes, her company has figured out how to help patients avoid having to give an inordinate amount of blood. There have been documented cases in which hospitals have drawn from patients in excess of 45 times the volume of blood than is necessary as a way of compensating for the possibility of rejected samples.

"We are very focused on the ability to mitigate the pain people who have to give blood frequently experience as their veins collapse from frequent blood draws," Holmes says. "This helps make it possible for little children to get tested without being scared, or for elderly patients, oncology patients, people whose veins are difficult to find."

Ultimately, her goal is to have testing sites within five miles of a every person's home. The startup took a major step in that direction back in September, when they it partnered with Walgreens to set up testing facilities at two locations in Palo Alto, California, and Phoenix, Arizona, with the possibility of expansion throughout 2014.