NEW YORK — Finger blood tests from Theranos, the medical startup, produced more irregular results than conventional tests offered by the nation’s two largest clinical laboratories, researchers reported Monday in the first published independent assessment of the company’s tests.
Theranos also came up with no answer at all for 2.2 percent of the measurements requested, something that virtually never happened with the two other labs, Quest Diagnostics and LabCorp.
The results, published in The Journal of Clinical Investigation, are not entirely negative. By and large, Theranos’s measurements agreed with those of the other labs, and cost much less. Still, the study is almost certain to raise more doubts about the company’s assertion that it had found a way to revolutionize medical testing.
On Thursday, Theranos sent a letter to the journal, hoping to stop it from publishing the paper. The letter, signed by its laboratory directors, called the study “flawed and inaccurate” and added, “We are disappointed that any journal would accept this study for publication.”
Theranos has attracted huge attention for saying that it could perform numerous blood tests at very low cost using a few drops of blood from a finger rather than the usual tubes of blood drawn from a vein in the arm.
The news media swooned over Elizabeth Holmes, who dropped out of Stanford to start Theranos and now, at age 32, is a billionaire on paper.
But articles in The Wall Street Journal and regulatory actions have challenged the company’s claims. Federal regulators in January cited Theranos for several deficiencies, including one that posed “immediate jeopardy to patient health and safety.” Theranos is no longer doing much finger-prick testing, pending regulatory approvals.
The new study, by researchers at the Icahn School of Medicine at Mount Sinai, was conducted for the most part last July, before the questions about Theranos arose.
The study involved 60 healthy adult volunteers, each of whom was tested twice in the same day at two separate walk-in Theranos sites in the Phoenix area. For Quest and LabCorp, the volunteers had blood drawn from their arms immediately before the first Theranos visit and again immediately after the second one.
They were tested for 22 measures, including various types of cholesterol and a complete blood count. The tests did not include one for the clotting ability of blood, the one Theranos executives say regulators cited as posing a threat to patients.
While most of the results were similar for the three labs, 12.2 percent of the measurements reported by Theranos were outside the expected normal range for healthy people, compared with 7.5 percent for Quest and 8.3 percent for LabCorp.
Theranos was out of range more often for lymphocytes, which are types of white blood cells; for a measure of hemoglobin; and for certain types of cholesterol. But Quest and LabCorp also differed from each other in some instances.
In their letter to the journal and in an interview, Theranos executives said that just because a result was out of the normal range did not mean it was wrong. There was no attempt made by the study’s authors to determine which measurement was correct.
Still, some experts not involved in the study said it was done reasonably well.
“This represents just another effort for a failing company to cover up bad press for a technology that is not ready for prime time,” Dr. Frederick L. Kiechle, medical director for clinical pathology at Memorial Healthcare System in Hollywood, Fla., said about Theranos’s letter to the journal.