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.)

This article originally appeared on Newser: Our Blood Can Change From One Drop to the Next

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