Factors that may interfere with the accuracy of a lab test include:

• Not following the instructions for how to prepare for the test. Some tests, such as a cholesterol and triglycerides analysis, require you to stop eating for at least 12 hours before the test. Other tests, such as a 2-hour postprandial blood sugar, require that you eat exactly 2 hours before the test.
• Some medicines or herbal treatments. For example, many medicines raise or lower blood sugar levels and could interfere with blood sugar tests. Birth control pills and some steroids can raise blood sugar, while some medicines to treat high blood pressure and depression can lower it.
• Drinking caffeinated beverages or alcohol.
• Eating meat, especially beef.
• Taking vitamins, especially vitamin C.
• Smoking or using other tobacco products.
• Stress.
• Strenuous exercise.
• Your occupation.
• Your distance from sea level.
• Pregnancy.

Follow your health professional's instructions to make sure that your test results are as accurate as possible.