By Billie Rubin, Hemoglobin’s Catabolic Cousin, reporting from the labs of Stanford Blood Center
A unit of red blood cells (RBCs) expires in 35 or 42 days because of the type of anticoagulant in the bag. But in real life RBCs live about 120 days (except for Scarlett O’Negative, she’s immortal). When they get old and their membrane starts to show wear and tear (like most of us), they get removed from the blood circulation in the spleen, liver and bone marrow at about the same rate as new ones get produced. It’s the original “sustainable” environment.
There are millions of RBCs in just one drop of blood. People who live at higher altitudes have more (like in the mountains of Peru). They are produced in the bone marrow of large bones at a rate of 2 million per second. In the minute it took you to read this, you made 120 million of them!