In the time it takes to read this sentence, your body will produce 17 million blood cells deep in its marrow. To put that in context, that’s as many cells as twice the population of New York City. Once created, those red blood cells move into the bloodstream—red blood cells, white blood cells, and platelets, all bobbing along in plasma through 60,000 miles of vessels in the human body.
And in the time it took you to read the first paragraph, all of the blood in your body has completed its regular journey—it has traveled from your heart to your extremities and returned, there and back again. Your blood knows your body better than your brain does, as your blood has seen all but the cornea, from the brain to the toes and everything in between. It has sailed on the quick current of the great arterial rivers and through the smallest cholesterol-clogged creeks. It has seen it all.
Because of this Hobbitesque journey, remnants of all of the battles waged by the white blood cells against the enemies of your body, foreign and domestic, persist in your blood. Evidence of aberrations developed over the course of your life lurks behind, indicating future problems on your health’s horizon.
Your blood is a biomarker. Biomarkers, according to epidemiologist Barbara Hulka, are “cellular, biochemical, or molecular alterations that are measurable in biological media such as human tissues, cells, or fluids.”
While your body has many types of biomarkers, blood is in many ways the most promising. Several drops of blood increasingly give doctors a multitude of physiological data about your health. It is thought that blood records all the biological events of your life.
For example, doctors can now analyze a drop ...1