It’s impressive what a doctor can determine about your health from a blood sample. After the physician’s assistant or nurse has sat you down to measure your pulse rate, blood oxygen level and blood pressure, the doctor looks through the numbers on the printout and can check the health of your cardiovascular system, liver and kidneys at a glance. They can also check for signs of diabetes and cancer.

The numbers seldom really lie. There are standards and norms against which our blood levels are measured that are well-defined and proven signs of a body in good health. Like most athletes, I’m as competitive about those numbers as any other in life.

It all starts with pulse rate. I wear my Garmin to sleep and lately it tells me that my overnight resting pulse rate is 45. That’s a pretty good sign.

Today the nurse took my blood pressure and it turned out to be 118/78. Again, pretty good. I was ahead in the blood tests so far. The oxygen level seemed off to her, so she plopped the finger clamp device on the table with a scoff and said, “Thing needs a new battery.”

Then the doctor came in and informed me that my cholesterol is still a little high. “Family history,” he said with a glum grin. He knew both my folks from years of medical treatments at the same family practice.

I take nothing for granted on any of these fronts. Recently some close friends that are also runners have had dramatic and frightening incidents from undetected heart disease. Some had considerable blockages in their arteries. I don’t want to be one of them.

Whenever I spill some blood in a bike crash it provides a bit of morbid fascination watching the oxygen go out of the stuff until it dries brown and lifeless. When I crashed into the downed tree on the bike trail a few years back I was riding at 20 mph with my head down. After running into the tree, I didn’t realize I was even cut on the face until the people who came up behind me stopped to ask if I was okay. I said, “Yes, I think so” as I stood up from the tumble I’d just taken.

“Because,” the woman pointed sheepishly at me with a wiggling finger pointed in my direction, “You’re really bleeding.”

Indeed I was. Blood was pouring out a genuine laceration on my chin. It would require a few stitches to sew shut the cut. The dried blood took days to clean up. And that’s the most we typically see our blood or think about it. By accident. Yet there it goes, everyday coursing around our arteries carrying oxygen and food to our muscles. On its way out and back it gets sticky in spots where plaque builds up. That’s where trouble can happen.

Thus the real “blood test” all of us face is how to deal with personal flaws in our blood level categories. Some might have problems that are lifestyle or diet-driven. Others have hereditary propensities to develop heart disease. Whatever the case, it’s up to us to face the results of every blood test on our own terms. It doesn’t matter what your neighbor or cousin or even brother or sister have experienced. Your blood is your own, and it’s up to you to pass the test on your own terms.

One of the big recommendations made by heart specialists is to get regular exercise. But that’s not a complete safeguard against potential problems inside your body. We’re as much about channels and flow as we are about carbon and dust. Blood is the life source we cannot take for granted, by any means.