Skip Navigation
The Pathways of Life
Dear "Ask the Doctor":
After a recent annual physical exam, my doctor's office informed me that
I have "elevated liver enzymes."
Now she says I need to come back for further tests. What does all this
mean, and am I in danger?"
Confused
Anytown, USA
Is Confused in danger? Could be; but most likely not. To get to the bottom of questions like this, doctors ask patients a lot of questions.
"How do you feel?"
"Have you eaten anything unusual lately?"
"On any new medications?"
And often, doctors will perform more tests, prompting the patient's body to yield a hint as to what's wrong—some clue as to why a most carefully maintained balance of natural chemicals has gone askew.
Like Confused, many of us have an encounter with biochemistry without even knowing it.
In health and in disease, our bodies are biochemical laboratories abuzz with activity, where molecules are constantly being made, used, broken down, and recycled. What does the lion's share of the work? Indispensable molecules called enzymes.
When routine blood tests reveal abnormally high liver enzyme levels, for instance, there are many potential causes, depending on which enzyme levels are awry and how off-kilter the levels are. The culprit could be as serious as alcoholism or infection with one of the hepatitis viruses, both of which can cripple the liver over time. Or the cause could be as innocuous as taking certain common medicines or having a few extra drinks at a party.
Many of the body's enzymes reside inside cells. If cells are damaged, they break apart and spill their contents into neighboring body fluids, like blood. The presence of higher-than-normal levels of enzymes in the blood can signify trouble in the tissues or organs (such as the liver) that those cells normally populate. But sometimes, abnormal lab results mean nothing at all. Elevated enzyme levels caused by the body's processing of "toxins"—including substances like chemicals in the environment, prescribed medicines, or alcohol—usually return to normal once the foreign substance is gone from the scene.
The liver is not the only place enzymes hang out. Every cell in every organ—from the liver to the heart to the skin—is chock full of enzymes. Anything but innocent bystanders, enzymes are the reason why cells are bustling centers of activity.
Enzymes underlie our ability to move, to think, to sense our world. Enzymes help us wink an eye, savor an ice cream cone, and catch a sticky drip about to fall off the edge of the cone. Enzymes, and their essential cellular associates—other proteins, nucleotides, sugars, and fats—allow a stubbed toe to heal properly and nurture a fetus growing inside a woman's body.
But when they are not working properly, enzymes can cause disease. Cancer can happen when the enzymes that copy the genetic material DNA make mistakes, giving rise to an errant gene that produces a faulty protein, or no protein at all. If that particular protein is the one that keeps a given set of cells from multiplying out of control, then its absence can bring about dire consequences.
Although a scientist may study a couple of isolated enzymes in the laboratory, inside the body enzymes are never lonely. They link up to form vibrant networks and pathways. The study of biochemical pathways and networks, and how they reverberate and influence each other, is the science of life and the chemistry of health.
In Control
It seems to happen the same way every time: You go to the doctor for a check-up, and a couple of days later, you end up with a cold. Your conclusion: Sitting in the doctor's waiting room made you sick. Believe it or not, this everyday situation resembles scenarios scientists face all the time in their labs. A scientist's perpetual challenge is to evaluate cause and effect, and then make conclusions. Key to this process is researchers' use of "controls." A scientist only knows for sure that A causes B if he or she knows that during the experiment, the presence of A was necessary for effect B to happen. That is—A doesn't also cause C, D, E, and F. Or, that B didn't happen on its own, without any input from A. In the waiting room example, for instance, it could be that going to the doctor truly does make you prone to getting sick, because in the waiting room, you are exposed to more germs than usual. But perhaps there's no relationship at all—just by coincidence you happen to get the sniffles around the time you go for your yearly checkup. Is it always in the spring when pollen counts are rising? Scientists must carefully design experiments so that they can account for the influences of as many variables as they can think of. Usually, researchers do this by comparing the test group with a control, or untreated, group. Only then do their experiments really "work."