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. ||||| blickwinkel / Alamy Stock Photo 
 
 Older people who received transfusions of young blood plasma have shown improvements in biomarkers related to cancer, Alzheimer’s disease and heart disease, New Scientist has learned. 
 
 “I don’t want to say the word panacea, but here’s something about teenagers,” Jesse Karmazin, founder of startup Ambrosia, told New Scientist. “Whatever is in young blood is causing changes that appear to make the ageing process reverse.” 
 
 Since August 2016, Karmazin’s company has been transfusing people aged 35 and older with plasma – the liquid component of blood – taken from people aged between 16 and 25. So far, 70 people have been treated, all of whom paid Ambrosia to be included in the study. 
 
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 Karmazin spoke to New Scientist ahead of presenting some of the results from the study at the Recode conference in Los Angeles today. These results come from blood tests conducted before and a month after plasma treatment, and imply young blood transfusions may reduce the risk of several major diseases associated with ageing. 
 
 Blood biomarkers 
 
 None of the people in the study had cancer at the time of treatment, however Karmazin’s team looked at the levels of certain proteins called carcinoembryonic antigens. These chemicals are found in the blood of healthy people at low concentrations, but in larger amounts these antigens can be a sign of having cancer. 
 
 The team detected that the levels of carcinoembryonic antigens fell by around 20 per cent in the blood of people who received the treatment. However, there was no control group or placebo treatment in the study, and it isn’t clear whether a 20 per cent reduction in these proteins is likely to affect someone’s chances of developing cancer. 
 
 Karmazin says the team also saw a 10 per cent fall in blood cholesterol levels. “That was a surprise,” he says. This may help explain why a study by a different company last year found that heart health improved in old mice that were given blood from human teenagers. 
 
 They also report a 20 per cent fall in the level of amyloids – a type of protein that forms sticky plaques in the brains of people with Alzheimer’s disease. One participant, a 55-year-old man with early onset Alzheimer’s, began to show improvements after one plasma treatment, and his doctors decided he could be allowed to drive a car again. An older woman with more advanced Alzheimer’s is reportedly showing slow improvements, but her results have not been as dramatic. 
 
 Reversing ageing 
 
 Instead of halting the ageing process, Karmazin says he thinks plasma transfusions actually reverse it. But if this is true, the effects don’t last forever. “Some people have felt great since they had the treatment 9 months ago,” he says. “Others have felt the effects wore off after a few months.” 
 
 Neither the intensity nor staying power of the treatment’s effects seemed to have any obvious relationship to the age of the people treated. “Whether you’re 40 or 80, the effect is really similar,” says Karmazin. “Ageing is just wear and tear.” 
 
 We all age at different rates, but Karmazin thinks that, on average, people will benefit most from receiving the treatment around twice a year. “We haven’t treated enough people to say with certainty.” 
 
 Many researchers are currently trying to chase down individual factors in the blood that may be responsible for any anti-ageing affects young blood may have. But Karmazin thinks the plasma’s rejuvenating properties come from the cumulative effects of many aspects of blood. “It’s not just one thing, there’s a lot going on.” 
 
 Placebo problems 
 
 The company’s trial has been criticised for having no placebo group. “There is no telling what may be down to the placebo effect,” says Arne Akbar at University College London. 
 
 The placebo effect is known to be able to influence biochemistry in the body. Because the treatment cost the participants $8000 each, it’s possible those involved would imagine any effects they felt to be bigger than they really were. 
 
 David Gems, also at University College London, would like to see more tests. “It would be best to be tested at several time intervals before and after the treatment, and ideally to have the tests done under similar conditions,” he says. “A single test before and after will be too anecdotal.” 
 
 Karmazin wants to do placebo-controlled studies, but it will be more difficult to fund these as people aren’t likely to pay thousands of dollars to possibly receive a sham treatment instead of young plasma.
– 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.)