The white coat effect
Some people's blood pressure rises at the clinic: the rush to get there, the waiting room, the nerves. The CDC calls this white coat syndrome and says that as many as 1 in 3 people with a high reading at the doctor's office may have normal readings outside it.
When the office readings are high but home readings are normal, doctors call it white coat hypertension. Home readings, or a 24-hour monitor, are how it is found.
Masked hypertension: the opposite
Some people have normal readings at the office but high readings in daily life. This is called masked hypertension, because the clinic reading hides it. A 2017 review in Current Hypertension Reports estimated it affects roughly 15–30% of people with a normal clinic reading in population studies, and treats it as a higher-risk pattern. Again, home readings or a 24-hour monitor are how it is found.
Other reasons readings differ
- Technique. Talking, crossed legs, an arm hanging down or a cuff over a sleeve can all raise a reading. See how to measure at home.
- Time of day. A morning reading at home and an afternoon reading at the clinic are not the same moment.
- Your monitor. Home monitors can drift. Take yours to an appointment once a year to compare it with the clinic's.
- The cuff size. A cuff that is the wrong size gives an inaccurate reading.
- Coffee, cigarettes, exercise within 30 minutes before a reading.
What to do about it
- Measure at home properly, at the same times each day, two readings each time.
- Keep a week of readings in a log and work out the average.
- Bring your monitor and your log to the appointment, so your doctor can compare.
- Let your doctor decide what the difference means. They may suggest a 24-hour monitor to be sure.
Not medical advice. This guide is general information. Your target, how often to measure and your treatment come from your doctor, who knows your situation.
Print a 7-day home logThe week of readings doctors ask for, with an average box at the end.Questions
Is white coat hypertension dangerous?
Ask your doctor. Researchers still study how much risk it carries, and some people with white coat hypertension go on to have high blood pressure at home too. That is why doctors keep checking.
How do I know if I have masked hypertension?
Only by measuring outside the clinic: home readings over a week, or a 24-hour monitor that your doctor arranges.
My home readings are lower. Can I stop my medicine?
No. Do not stop or change blood pressure medicine without talking to your doctor, whatever your home readings show.
Which reading is the real one?
Both are real. Home readings over several days usually give a better picture of everyday blood pressure, which is why doctors ask for them.
How do I calm down before a reading at the clinic?
Arrive early, sit quietly, and ask for a second reading at the end of the visit. Bringing your home log also helps your doctor see the bigger picture.
Sources
- CDC. Measuring Your Blood Pressure
- Anstey DE, et al. An update on masked hypertension. Current Hypertension Reports 2017;19(12):94
- American Heart Association. Monitoring Your Blood Pressure at Home
- 2025 AHA/ACC/AANP/AAPA/ABC/ACCP/ACPM/AGS/AMA/ASPC/NMA/PCNA/SGIM Guideline for the Prevention, Detection, Evaluation and Management of High Blood Pressure in Adults. Hypertension 2025;82(10):e212–e316