Reasons to fast before a blood test

Q: I hate not eating for hours and hours before a blood test. Is it really necessary? — Craig M., Schenectady, New York

A: It all depends on what you’re being tested for. If your doc is testing for diabetes using a fasting blood glucose or oral glucose tolerance test, you’ll fast overnight (That’s because your blood glucose level fluctuates a lot when you eat or drink anything but water, plain coffee or black tea. But the test for your

A1C levels — a measure of your average glucose level over the past three months — doesn’t require fasting. You also will need to fast for eight to 12 hours if you’re having your B-12 or iron checked. If you don’t fast like the doctor ordered, you could be misdiagnosed.

On the other hand, there are conflicting ideas about the importance of fasting before an HDL or LDL cholesterol check. New guidelines published in the European Heart Journal and JAMA Internal Medicine in July 2016 say that for blood lipid testing, “a nonfasting blood draw has many practical advantages.” Translation: Your doctor will let you know if you should fast.

Q: Is there any difference between this year’s flu shot and last year’s? And if there isn’t, do I still need to get one? — John E., Lansing, Michigan

A: There always is a difference. The influenza vaccine is adjusted to target the flu strains that experts predict will be most prevalent, which can change from year to year. New vaccinations are based on information from 142 national influenza centers in 113 countries. Scientists from the World Health Organization Collaborating Centers for Reference and Research on Influenza analyze the data and decide which strains of the virus are most likely to cause illness in the upcoming flu season. That’s why you should get inoculated annually.

Plus, protection from a yearly flu shot can add up: If you receive the flu vaccine every year for 10 years, you’ll reduce your risk of getting the flu by over 70 percent. And if you do get the flu, it’ll be much less severe.

2017 flu vaccine facts:

■ The nasal mist with a live attenuated influenza version (LAIV) of the vaccine is NOT recommended for anyone.

■ Anyone 6 months or older should be vaccinated. Pregnant women should receive their age-appropriate influenza vaccine.

■ Needle-shy? Fluzone Intradermal Quadrivalent vaccine for folks 18-64 has a 90 percent smaller, 1.5-mm microneedle.

Email questions for Mehmet Oz and Mike Roizen to youdocsdaily@sharecare. com.