Medical tests usually seem pretty cut-and-dried, but they're surprisingly easy to skew. Something as seemingly benign as eating the wrong thing can give bogus results, and now research suggests that you can affect blood pressure readings by just moving your arm. A study published in the Annals of Internal Medicine showed that shifting your arm from down at your side to straight out in front of you can reduce your blood pressure numbers up to 10 percent—sometimes enough to put you in an entirely different category of risk for heart disease. According to the American Heart Association, the best position is something in between: seated, with your forearm resting on a level surface and the cuff at the same level as your heart, putting your upper arm at a 45-degree angle from your torso.
Other Simple Slip-Ups That Alter Results
Blood sugar: The most common test is fasting blood glucose, which means no food or drink (other than water) for at least eight hours before your blood is drawn. Anything you consume during that time—especially sugary snacks or alcohol—can affect the results, as can hormonal birth control, estrogen, Dilantin (an anticonvulsant), blood pressure medications, diuretics, corticosteroids, certain antidepressants, and niacin (a vitamin that's used in high doses to lower cholesterol). Inform your physician if you're taking any of these.
Cholesterol: Results can be distorted by some diuretics, corticosteroids, certain antibiotics, and estrogen. Tell your doctor if you're on any medications. Physical stress, like that from acute illness or infection, can cause depressed HDL (good cholesterol) and higher triglyceride (fatty acid) readings.
Pap smear: Having sex or using vaginal douches, creams, lubricants, tampons, or medications (like those for a yeast infection) at least 24 hours before a Pap may wash away, mask, or boost the number of abnormal-looking cells, making results difficult to interpret. Blood can also interfere with the outcome, so schedule the test for a time when you won't have your period.
Fecal occult blood test: Since it screens for blood in the stool, don't take the test during your period and avoid red meat for three days beforehand—both may cause a false positive and lead your doctor to order an unnecessary colonoscopy or sigmoidoscopy. Turnips, cauliflower, broccoli, bananas, melons, beets, radishes, and vitamin C and iron supplements can also skew the results. So can drugs: In the week leading up to the test, you shouldn't take anti-inflammatories like Advil or more than one daily dose of aspirin.