My wake-up call these days is not under my control. Rather, in the wee hours of the morning, a vampire of sorts will appear wraith-like at my bedside, wrap a tourniquet around my upper arm, and insert a hypodermic needle into my cephalic vein. While this does not make for the most pleasant of awakenings I understand well why this bloodthirstiness is part of the hospital routine.

Every medical specialist thinks their part of the body is the most important. No one person can possibly claim to know the whole so we’ve broken it down into component parts. Fellowships in hand surgery, for instance, take years atop already-lengthy residencies; our prehensile thumbs didn’t evolve quickly, nor are they easily fixed.

But there’s also a price to pay for balkanizing human organ systems: it warps the vision. Apprenticeships don’t lead to union among doctors, but competition. To justify your concentration on one field as anything more than myopia, you convince yourself through so much study that your piece of the puzzle is the most crucial. Put in enough sweat equity learning the intricacies of the gallbladder and you’ll become an evangelist for the integral role it plays in our anatomy. I’ve heard more than one nephrologist describe the kidney as “the seat of the soul” while others may just perceive a dirty filter that produces urine, not a cathedral but a wastewater plant. Self-actualizing philosopher Rene Descartes thought the pineal gland was the connection between mind and spirit, though it will remain invisible at the base of the brain to all but a few intrepid neurosurgeons.

This is all sour grapes, of course, because the cardiologists have already decisively won the PR battle as apostles of the Most Important Organ. Laymen identify the heart as the center of our being; I’m less smitten. I am convinced, of course, of its irreplaceable value as a pump, but it’s only useful when filled. Valentines may owe their (rough) shape to the heart, but not their color. Even the Cupid-besotted public would be surprised by the true appearance of the organ in isolation. It becomes a pale imitation of itself when its chambers are empty.

An engine needs fuel, and humans run on blood, richer than the highest-octane gasoline and arguably more volatile. It won’t evaporate quickly but the liquid is in a constant state of flux. Your entire supply of red cells is replaced every 120 days. Three times a year, all the circulating erythrocytes are turned over.  After months of being forcefully ejected by the left ventricle into the aorta to rocket around the circuit of vessels -- squeezing through capillaries to deliver their oxygen cargo before returning hungrily to the lungs -- their membranes start to erode. As a final act of generosity they return their iron core to the body as if being smelted down into raw materials.

Other cells, like your platelets, have much lesser longevity; your first responders to injury, they last only a week, less than that if you injure yourself and they gather to plug nicks and cuts. Summoned from the blood to sites of vascular damage, they lay themselves down over a wound like a quick-to-congeal liquid bandage, going only once unto the breach. The lifespan of the platelet is nasty, brutish, and short, existing to serve us through sacrifice as we are buffeted through life’s traumas.

Elsewhere memory cells issue forth, lymphocytes testifying to your past movements through a dirty world. Stalwart sentinels recall every breath you take, every surface you graze: daycare coughs & recirculated airplane cabins, elevator buttons & hotel remotes, all the ways you’ve been in the microbial company of others. They tell a nightmarish tale to a germaphobe, a chronicle of contact they’d love to forget. Only the heaviest-duty chemotherapy and a bone marrow transplant can render you amnestic of these invisible communions, a lifelong record that persists in the bloodstream even after the mind it irrigates is lost to dementia.

So yes, I can tell a lot about a person by looking at them, but I can tell even more from their vital humors. Hand me a sharp object and I can show you what a man is made of. I’m no centurion at Calvary so let me use a syringe rather than a spear, collecting his precious serum in sterile glass instead of a chalice. From there, as a hematologist, I can peer into the blood's depths, judge its hue, time how quickly it clots, test what defense it bears against infection and injury. A centrifuge can separate out the different cell types by their density, the white cells and platelets forming a buffy coat that floats above the red cells while suspended beneath the plasma: tricolor Neapolitan layers in a test tube.

This is all to clarify & excuse why most of my own visits with patients are coupled to phlebotomy, so that I might complement their signs & symptoms with a measurement of their counts. The qualitative and the quantitative make for an instructive pair.  

A complaint of fatigue is easily explained by a low hemoglobin, then remedied with a transfusion of red blood cells from a matching donor healthy and thoughtful enough to spare a pint or two.

The severity of a fever is best assessed by numbering the neutrophils, those patrolling leukocytes that engulf bacteria on contact: too few and the immunosuppressed can quickly turn septic. We aim to intervene in a neutropenic patient before such a crisis by responding to a temperature spike with broad-spectrum antibiotics, offering blanket coverage against dozens of microbial species.

For a doctor who has observed a patient’s friable gums, enumerating the platelets can then distinguish garden-variety gingivitis from an imminent risk of life-threatening hemorrhage. There is more than a slight difference in management between remedying poor dental hygiene and forestalling massive internal bleeding.

And so we track numbers as closely as a day trader following fluctuations in the market. Misunderstanding this medically justified habit of collecting & counting cells, my more suspicious patients will sometimes accuse me of baying for blood. When I walk by the lab I can see their oozing wrists and balled fists. Some of those fists never unclench, fractious to the end, but all bleeding stops eventually. Before then, I try to dispel mistrust, to disprove conspiracy theories about my lupine tendencies. I hope they can apprehend my thirst for real-time data, the value I place on in vivo samples exported in vitro for analysis.

It’s natural to resent the sharp poke, but they should know that all the venipuncture is not ritual sacrifice, ordered to satisfy a sadist desiring human pincushions. Rather, it represents an informed attempt to protect them -- and, now, me -- from the wolf at the door.

Mark Lewis