It seems like getting your blood pressure level measured should be pretty simple. After all, it's something that healthcare professionals often do dozens of times a day.

Yet research suggests that nearly a third of readings done in doctors offices are inaccurate. That's partly because of "white coat" hypertension, where your blood pressure is normal at home but spikes at the doctor's office, perhaps because of anxiety.

Or your physician or nurse simply may not take your blood pressure correctly, says Nieca Goldberg, M.D., a cardiologist and director of the Joan H. Tisch Center for Women’s Health at the NYU Langone Medical Center. Here’s how to do the test right, whether at home or in the doctor’s office.

Double-check your drugs. Certain medications, such as over-the-counter decongestants, prescription amphetamines, and the steroid prednisone, can increase blood pressure. So make sure your physician knows all of the drugs you take. 

Go to the bathroom first. A full bladder can raise blood pressure by as much as 15 points systolic (the top number) and 10 points diastolic (the bottom number). 

Sit correctly. Your back should be straight and supported, with you seated on a chair rather than, say, on the examining table. Your feet should be flat on the floor, with your legs uncrossed. Your arm should be supported on a flat surface (such as a table) with the upper arm at heart level. 

Measure twice. If your blood pressure reading is high, your doctor or nurse might measure your pressure again at the end of the exam, when you’re usually more relaxed, Goldberg says. The lower reading is usually more accurate. 

Remain quiet. Talking can raise your blood pressure by up to 10 points on either the top or bottom number. 

Check the cuff. Blood pressure readings taken over clothing or with too small a cuff can boost blood pressure by as much as 50 points.