13 Things You Should Never Do Before a Medical Test
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.
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