Red Blood Cells (IMAGE) Duke University Caption Red blood cells ferry oxygen to tissues, providing fuel for muscular activity. Unscrupulous athletes have been able to 'dope' their blood by enriching their supply of red blood cells. But a new test of microRNA can tell old cells from new ones. Credit Bruce Blausen via Wikimedia Commons Usage Restrictions Must credit Bruce Blausen License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.