For a growing number of medical startups, the holy grail is to develop technology that can diagnose hundreds of diseases with a single drop of blood. 
 
 Many people are squeamish about getting their blood drawn by traditional methods, such as inserting a long needle into a vein. And in developing countries, health clinics are eager for "lab on a chip" diagnostics that can be done without piercing a vein. 
 
 But researchers are finding myriad challenges with relying on a single blood drop. In a recent experiment, scientists at Rice 360° Institute for Global Health took seven drops of blood from 10 individuals. They tested each blood drop for basic health measures, such as hemoglobin and platelet counts, and found a wide range of results between drops that came from the same person. 
 
 "These data suggest caution when using measurements from a single drop of fingerprick blood," researchers Meaghan M. Bond and Rebecca R. Richards-Kortum concluded in The American Journal of Clinical Pathology. 
 
 Bond and Richards-Kortum told the New York Times that in order to achieve results as accurate as conventional methods—the venous blood draw—they had to average six to nine drops of blood from each individual. 
 
 In recent months, Theranos, a company that hoped to revolutionize the blood-testing industry, has come under fire from federal regulators. Theranos's CEO Elizabeth Holmes once promised to detect dozens of medical conditions, from high cholesterol to cancer, based on a few drops of blood. 
 
 San Diego-based Genalyte is also working on a diagnostics system to produce test results from a single blood drop. But unlike Theranos, Genalyte has generated a number of peer-reviewed studies to validate its approach. The company is focusing initially on autoimmune diseases, such as lupus and rheumatoid arthritis. ||||| , cost as little as $3.40 
 
 Some tests, such as 
 
 At 19-years-old, Elizabeth Holmes dropped out of her chemical engineering degree at Stanford University and used her tuition money to pursue a business idea she hoped would change the landscape of healthcare. 
 
 With a major fear of needles, she decided the current system for testing blood - implemented in the 1960s - was archaic, expensive, painful and slow. 
 
 Holmes, 30, endeavored to change that method and develop a way that would eradicate the need for vials of blood to be taken and for blood tests to have to take place at the doctors or a lab. 
 
 Working mostly in secret for the last 11 years, her company, Theranos, is now valued at $9 billion and, according to Holmes, is changing people's lives. 
 
 Scroll down for video 
 
 Revolutionary: The CEO of diagnostic center Theranos, Elizabeth Holmes, 30, is the brains behind a $9 billion company that has changed the medical landscape by developing a new method to run blood tests 
 
 Theranos' technology requires only a finger prick of blood to be drawn from a patient in order to get fast, effective results. 
 
 One drop can run 30 lab tests, the company claims. 
 
 Holmes told Wired they can get results in less than four hours. 
 
 She said that her fear of needles allowed her to realize that people avoid blood tests for that reason. 
 
 Partnered with Walgreens, the flagship Theranos Wellness Center is based in Palo Alto, California. 
 
 There are also 20 others that have opened inside Walgreens around Phoenix. 
 
 Patients are able to walk into the stores, have their finger pricked, and get blood results within hours. 
 
 The cost, depending on the extent of the tests, averages around $30. 
 
 Holmes' goal is to launch Theranos in all 8,200 Walgreens across the country. 
 
 'Our work is enabling everyone, no matter how much money they have, or where they live, or what kind of insurance they have, to be able to have access to the kind of testing information that could change their lives,' she told USA Today. 
 
 'Theranos is a company dedicated to the belief that access to actionable health information at the time it matters most is a basic human right.' 
 
 Leader: Theranos Chairman, CEO and Founder Elizabeth Holmes and TechCrunch Writer and Moderator Jonathan Shieber speak onstage at TechCrunch Disrupt at Pier 48 on September 8, 2014 in San Francisco 
 
 'Archaic': Holmes decided the current method for testing blood, requiring one or multiple vials of blood and first introduced in the 1960s, was out-of-date and needed to be streamlined 
 
 New system: Theranos developed software that allowed blood tests to be performed using a 'micro-sample', needing just a drop of blood taken from a person with a finger prick 
 
 Menu: Now in 21 locations - a flagship in California and 20 smaller clinics in Phoenix - Theranos charges different amounts for their blood tests, depending on what is being tested 
 
 Now 30, Holmes was the youngest self-made woman on this years Forbes 400 rich list. 
 
 Shes owns 50 percent of Theranos, and has a net worth of about $4.5 billion. 
 
 'She could totally overturn an entire industry if Theranos is as successful as it seems to be,' Abram Brown, associate editor at Forbes, told Yahoo. 
 
 Holmes has a team of influential backers behind her company. 
 
 The Theranos board of directors includes former secretaries of State Henry Kissinger and George Shultz, former Defense Secretary William Perry, and former senators Sam Nunn and Bill Frist. 
 
 Holmes is getting great responses from patients using the Theranos diagnostic centers. 
 
 Dropout: Holmes left her chemical engineering degree at Stanford to develop a way to take the pain and cost out of getting blood tested. She is now worth $4.5 billion 
 
 She told USA Today of a diabetic woman who wrote to her that had three fingers picks for a wide-range of blood tests. 
 
 She paid $34. 
 
 The woman said she had undergone the same tests earlier this year and that it cost her insurance $876. 
 
 'When I realized this is what I wanted to do with my life, things got easy,' Holmes told USA Today. ||||| Photo Advertisement Continue reading the main story 
 
 LAGUNA BEACH, Calif. — Being the self-proclaimed leader of a medical revolution can have its downside. 
 
 
 
 
 
 
 
 
 
 Elizabeth Holmes, a 31-year-old Stanford dropout who became a billionaire by starting the blood testing laboratory Theranos, is now waging a public battle to defend her reputation and that of her closely watched Silicon Valley company. 
 
 Her campaign began shortly after two articles published in The Wall Street Journal last week questioned the accuracy of the company’s blood tests and the extent to which Theranos is using unique technology. 
 
 Ms. Holmes now says she is planning to release a 16-page point-by-point rebuttal of the articles, a document that concludes by accusing the articles’ author of having an agenda that considered Theranos “a target to be taken down.” 
 
 The rebuttal even dissects the motivations of various people quoted in the articles. 
 
 “We’ll put this out there and let people judge for themselves what the facts are,” Ms. Holmes said on Tuesday in an interview with The New York Times. 
 
 Ms. Holmes ventured into the lion’s den on Wednesday, defending her company in an onstage interview here at The Wall Street Journal’s own WSJ.DLive technology conference, where she drew applause for showing up. 
 
 “We know the integrity of what we’ve done,” Ms. Holmes said at the conference. She characterized criticisms of her company as “a few people who want to say bad things about us.” 
 
 Ms. Holmes has complained that critics are out to get her company because it threatens the traditional lab industry. 
 
 But the company, which is highly secretive about its technology, has not announced any new policies in response to the criticism. 
 
 Theranos, Ms. Holmes said, had no immediate plans to do what skeptics say would most persuade them: publish data in peer-reviewed medical journals showing that its test results were as accurate as those of more established laboratories. 
 
 She said that other institutions testing Theranos’s products might eventually publish papers, but that the company, for now, was concentrating on getting its tests approved by the Food and Drug Administration. That, she said, would provide even better external validation. One test, for herpes simplex 1 virus, has already been approved, and the company has submitted 120 others to the agency. 
 
 Advertisement Continue reading the main story 
 
 “We’ve never been against peer review,” Ms. Holmes said in the interview with The Times. “We decided that the studies we were doing would be the F.D.A. submissions.” 
 
 Theranos, based in Palo Alto, Calif., says that it can do many different medical tests using only a tiny amount of blood taken with a finger prick. It has also said that it used proprietary lab equipment to deliver results much faster and more cheaply than traditional blood tests, which in some cases require several vials of blood to be drawn from the arm and several days to get a result. 
 
 Photo 
 
 Theranos lists the prices of its tests on its website, and they are typically far lower than most other labs’ prices. 
 
 Investors have poured money into the privately held company, which was recently valued at more than $9 billion. Ms. Holmes, who started the company at age 19 and has said that she devotes nearly every waking hour to it, has graced the covers of magazines including Fortune, Inc. and The New York Times’s T magazine, and she is a frequent presence on the conference circuit. She recently appeared at Vanity Fair’s New Establishment Summit alongside Facebook’s chief executive, Mark Zuckerberg, and Walt Disney’s chief, Robert A. Iger. 
 
 Advertisement Continue reading the main story 
 
 Advertisement Continue reading the main story 
 
 The Wall Street Journal article last week, citing an unnamed former senior employee, said that as recently as December, Theranos was routinely performing only about 15 of the more than 200 tests it offered using its proprietary equipment, with the rest being performed on standard machines bought from laboratory equipment vendors. 
 
 In its rebuttal, which Theranos plans to post on its website the company said that it performed more than 80 of the tests using its own technology that month. It said that 57 percent of customers in the fourth quarter of last year had blood drawn from a finger prick. 
 
 Last week, the company said that it was not using finger pricks at the moment — except for the herpes test — because it was following F.D.A. advice that its “nanotainer,” the tiny tube that holds the blood from finger pricks, needed regulatory approval as a medical device. The company is now seeking that approval. But Ms. Holmes said that the need to get approval for the tube did not reflect on the accuracy of the machines that analyze the blood samples. 
 
 A spokesman for The Wall Street Journal thanked Ms. Holmes for attending the conference but added, “Nothing said at the conference by Ms. Holmes refutes the accuracy” of the articles. 
 
 The Wall Street Journal is not the only one raising questions. Jean-Louis Gassée, a former senior executive at Apple, wrote in a blog post on Sunday that the results of two tests from Theranos raised alarms about his health when results for the same tests on the same day from Stanford Hospital did not. Moreover, the Theranos results varied more widely from one day to the next than those from Stanford, he said. 
 
 In January, William Quirk, an analyst at Piper Jaffray, wrote that a member of his team had gone for common blood tests at a Theranos center in Phoenix and at two hospitals. The Theranos results came back in 70 hours, compared with about 25 hours for the other two labs, despite Theranos’s claim to deliver “results in hours, not days.” 
 
 At the conference here, Bill Maris, the head of venture capital firm GV, formerly known as Google Ventures, told The Times that when the company was thinking of investing in Theranos, one of his employees went to a Walgreens pharmacy for a Theranos blood test and was later asked to return to give more blood. Theranos did not seem able to deliver on its promise of testing small amounts of blood, he said. Business Insider reported earlier on Mr. Maris’s remarks. 
 
 Ms. Holmes said that she had never spoken with Mr. Maris and that GV had once “reached out to us and we said no to meeting them.” She said a few anecdotes did not cast doubt on the technology, asserting that the company has done more than 3.5 million tests. 
 
 Ms. Holmes said the company has always said that some tests would require more conventional blood draws, though even for those, she said, Theranos tends to use smaller needles and smaller amounts of blood than other labs. She said the company wanted to provide a complete roster of tests, so it began offering tests that could not yet be performed with finger samples on its own machines. 
 
 Still, this caveat about conventional blood draws has often seemed more like a footnote for a company that has at times proclaimed, “Say goodbye, big bad needle.” Certainly, the impression from interviews and numerous articles has been that Theranos performed the vast majority of tests using finger pricks and its proprietary machines. 
 
 “The general public was under the impression that Theranos was further along in their development than they currently are,” said Eric Lakin, an analyst at DeciBio, a consulting and market research firm that follows the diagnostics industry. 
 
 Mr. Lakin said he thought that Ms. Holmes, in her talk at the conference, “directly addressed many of the concerns people raised.” 
 
 Nonetheless, he said, “There’s still going to be doubts about why won’t you compare your results directly” with those from established labs like Quest Diagnostics and LabCorp. While Theranos does post some performance data on its website, it is not sufficient, he said.
– As doctors shift away from drawing vials of blood from patients and rely on lab-on-a-chip diagnostics that identify a myriad of conditions using a single drop of blood, there's now concern that not all of your blood is equal. A new study in the American Journal of Clinical Pathology suggests "caution when using measurements from a single drop of fingerprick blood," write researchers at Rice 360° Institute for Global Health: Our blood can change rather dramatically from one drop to the next. Researchers tested seven drops of blood from each of 10 participants and analyzed them for basic health metrics such as platelet counts and hemoglobin, and found a pretty wide range of results—so much so that they had to average the results from six to nine drops to rival the accuracy of a larger blood draw from a vein, reports the New York Times. "If you’re going to take a fingerprick stick to get your measures, you need to be aware that you’re sacrificing some accuracy," one of the researchers warns. The results have implications for startups like Theranos and Genalyte, which hope to diagnose diseases using only one drop. Unlike Theranos, however, Genalyte has produced results via peer-reviewed studies on tests to find autoimmune diseases such as lupus, reports Fast Company. (The Theranos founder dropped out of college at 19 to start the company.)