Men spill it, seal friendships with it, and, if they're aging rock guitarists, have it purified at Swiss clinics. But blood also tells a detective story. Just as the amount, color, odor, and feel of the oil on a car's dipstick offer clues about wear and tear on the engine, your blood can reveal critical details about the running condition of your entire body.
Of course, first you need to know what to look for and how to interpret the findings. That's why we've created a guide on how to read the red stuff. Order up all seven of these tests at your next physical and you'll be doing more than just kicking the tires.
Start with the basics: the CBC
"If I had a 30-year-old man coming to me for the first time, I'd order a complete blood count (CBC)," says David Perkins, M.D., an internal-medicine physician based in St. Davids, Pennsylvania. Think of the CBC as an array of baseline numbers for key factors such as red (oxygen-carrying) blood cells, white (infection-fighting) blood cells, and platelets (clotting particles).
Within the CBC, a hematocrit score indicates the proportion of red blood cells in your total blood volume, and a hemoglobin measurement assesses the oxygen-carrying protein of red blood cells. "If you've been following the exercise and nutrition advice recommended in this magazine and are still short of breath while pumping iron, you may have low hematocrit and hemoglobin counts," says John A. Elefteriades, M.D., chief of cardiothoracic surgery at Yale University and the coauthor of Your Heart: An Owner's Guide. These low numbers may signal anemia, a blood disorder that can lead to heart arrhythmia if left untreated.
If your blood is anemic: The good news is that you can treat some types of anemia by taking an iron supplement (best absorbed 30 minutes before breakfast with orange juice or vitamin C). Supplemental vitamin B12 or folic acid can also help.
Learn your sugar score
Blood tests are like radar for tracking type-2 diabetes. The standard measure is the fasting glucose test, which is part of what sounds like a congressional subcommittee: the Comprehensive Metabolic Panel. Fasting glucose is a one-off reading, so it's often paired with the A1c test of your average blood-glucose level over the preceding 2 to 3 months.
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But if you score high on either of these tests—above 100 milligrams per deciliter (mg/dl) on the fasting test, or above 6 percent on the A1c — you should demand an oral glucose-tolerance test (OGTT). "Doctors diagnose heart disease with a stress test, not a resting test," says Keith Berkowitz, M.D., medical director of the Center for Balanced Health in New York City. "An OGTT does the same for the most basic process in your body — metabolism." As Dr. Berkowitz points out, the fasting measure can still be in the normal range even if postmeal numbers are elevated. As for the A1c, it can miss some abnormalities because swings from high to low blood sugar sometimes simply average out.
Take an OGTT regardless of your fasting-glucose and A1c scores if you score 140 mg/dl or higher on a random glucose test (one you take without fasting beforehand), your belly's bulging (that is, your body mass index is 30 or higher), or you experience head-snapping slumps after a high-carbohydrate meal. Ditto if you have a family history of diabetes or heart disease. The test can last 2 to 5 hours, depending on the version you take. If you hit the 2-hour mark of an OGTT with a reading above 140 mg/dl, you're prediabetic. If it's above 200 at that point, there's no "pre" about it.
If your blood is too sweet: Shed pounds, if you're one of the 80 to 90 percent of people with type-2 diabetes who are overweight. Slashing carbs from your diet and hitting the treadmill for 15 to 20 minutes a day should do the trick while offering the added benefit of increasing your insulin sensitivity.
Keep an eye on fats, too
"The fasting lipid profile is where cardiovascular abnormalities are most likely to appear for the average guy," says Dr. Perkins. Generally, your HDL (good) cholesterol should be between 45 and 50 mg/dl, while your LDL (bad) cholesterol should be below 130 mg/dl. Triglycerides should fall under 150. If you have risk factors for cardiovascular disease — such as past cardiac events, a family history of the disease, hypertension, or you're a smoker — your target LDL may be below 100 mg/dl. If you're at high risk, ask your physician about an expanded lipid profile test, like the Vertical Auto Profile, which further breaks down the dangerous subtypes of LDL.
If your results don't measure up: If your HDL is too low, tossing walnuts into your yogurt may raise your good cholesterol by 9 percent, according to a study in Angiology. If your triglycerides are high, cut back on starches, breads, pasta, and other carb-loaded offerings. Even if your LDL levels don't go down, you can still halve your chances of dying of a heart attack simply by exercising, according to a joint study by the Cooper Institute and Canada's Queen's University.
Look for signs of inflammation
The process by which inflamed arteries lead to cardiovascular disease is invisible except for a tracer — an elevated level of C-reactive protein (CRP) in your blood. "If your CRP as well as your total cholesterol is high, you're at an even greater risk of having a heart attack than you would be with either risk factor by itself," says David Sandmire, M.D., a professor of physiology at the University of New England in Biddeford, Maine.
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Make sure you feel perfectly healthy the day of your appointment: This highly sensitive test picks up all sorts of inflammation, even from a paper cut. That's a good reason to take it twice, at least a month apart, and average the two scores. Yours should fall under 1 milligram per liter; if it's above 3, your heart-attack risk doubles.
If your score is too high: Smokers, take note: "It's almost certain that CRP levels will decrease after you quit," says David W. Johnson, Ph.D., an associate professor in the college of osteopathic medicine at the University of New England and coauthor of Medical Tests That Can Save Your Life. If your lungs are already a smoke-free zone, raise a glass. A Spanish study found that red wine reduced inflammation markers by 21 percent.
Have your prostate checked
More than 180,000 American men will be diagnosed with prostate cancer in 2008, so pay great attention to tracking your prostate-specific antigen (PSA). Elevation of this marker can signal a problem — at least sometimes. "PSA testing is not an exact science, because factors external to the prostate can cause the marker to rise," says Johnson. A high PSA reading may point to a benign enlargement of the prostate or even a bacterial infection known as prostatitis.
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That's why the trend can be as important as the static number. "Every year I have a PSA test done along with my physical, and compare the result with that of the year before, to see if further investigation is warranted," says Johnson. "Once you reach 50 years of age (40 if you're African American), your doctor may recommend a PSA test. Don't hesitate to ask for one if you're in your 30s, however.
Keep your results in range: Eat two Brazil nuts a day, good for 200 micrograms of selenium. National Cancer Institute researchers found that men with the highest selenium levels who also took a multivitamin were 39 percent less likely to develop prostate cancer than those with the lowest levels.
Don't forget your thyroid
Thyroid problems hit men as well as women, and stress and poor sleep are often the culprits. "Many people don't sleep as well as they should, so the body overcompensates," says Dr. Berkowitz. With an overactive thyroid, there may be signs of a goiter — a swollen area in the neck. Hyperthyroidism, as it's called, can also lead to an increased heart rate, anxiety, sleep problems, and weight loss. Symptoms of an underactive thyroid (hypothyroidism) may include personality changes, hair loss, weight gain, and a cloudy memory. Both thyroid conditions can lead to more serious, life-threatening illnesses when left untreated. The thyroid-stimulating hormone (TSH) test will determine if you have a problem.
If your results are off the mark: Your doctor may order the more specific free T3 and free T4 follow-up tests. Depending on whether your thyroid is overactive or underactive, a beta-blocker or thyroid-hormone replacement drug may be prescribed.
Check one final thing
"Aspirin, although a very old and cheap product, is really a wonder drug," says Dr. Elefteriades. That's because aspirin reduces the stickiness of platelets, making them less likely to clump together and block a blood vessel. But not all men respond to this treatment — and there's a test that identifies the ones who don't. "Aspirin resistance is found in about 20 percent of patients tested," says Eric J. Topol, M.D., dean of the Scripps School of Medicine in La Jolla, California. For those men, aspirin is a waste of time and money.
If you're aspirin resistant: Cook with virgin olive oil. Three tablespoons a day can help improve arterial bloodflow, Spanish scientists found.