What can affect the accuracy of a blood pressure reading?
When you measure your blood pressure yourself, there are a few things to keep in mind to get accurate readings. It is well known that measurements should be taken at rest - both physically and mentally - while sitting or lying down. It is also easy to understand that you should measure before taking your medication. Only then are the readings comparable.
But why shouldn't you speak during the measurement? How can breathing influence the process, and why shouldn't you smoke beforehand? What happens if, when measuring with a wrist device, the arm is held too high or too low? We looked into these and other questions.
Do you have to take off your jacket, sweater and similar clothing to measure?
Every blood pressure cuff contains a sensor. Most cuffs work on the oscillometric principle - they detect the vibrations caused by the pulsating blood when the cuff is inflated and deflated. The blood pressure is then calculated from these signals. If there is a thick sweater, a jacket, or one or more folds of fabric (for example from wide sleeves) between the sensor and the artery, the sensor can no longer detect those vibrations, resulting in incorrect measurements.
Therefore, the arm should be uncovered for the measurement. Only garments with very thin, close-fitting sleeves may be left on if necessary.
Is it enough to push up the sleeve of a sweater, shirt, blouse, etc.?
This question mainly concerns measurements with an upper-arm device. But even when using a wrist device, a pushed-up or rolled-up sleeve can distort the measurement. This is because rolling or pushing up the sleeve makes it tighter, or because narrow parts of the sleeve do not fit over thicker parts of the arm. If this constricts or strongly compresses the arm, the arteries are narrowed before the blood pressure cuff, and the blood pressure measurement can no longer produce accurate results. Therefore, only garments that are loose enough should be rolled or pushed up.
The correct cuff size is important!
The blood pressure cuff-that is, the part of the device placed on the upper arm or wrist-must fit you. Both the length and the width of the cuff must be suitable for your upper arm or wrist. The problem of an ill-fitting cuff occurs more often with upper-arm devices than with wrist devices.
The width of the upper-arm cuff should be chosen so that it can be placed two to three centimeters above the elbow crease. The cuff must fit snugly around your upper arm. Many cuffs have a mark that shows whether the cuff fits. Another mark often helps you position the cuff correctly so that the sensor lies over the artery and can record the oscillations. A cuff that is too wide or too short may produce falsely high readings. If in doubt, measure your upper-arm or wrist circumference before buying a device and take this into account when choosing one.
What happens if the measurement point is too high or too low?
Why shouldn't you speak during the measurement?
Talking in this context is a form of exertion that can raise blood pressure readings. As a result, the body is not at rest. In addition, speaking can interfere with the device during the measurement, causing it to stop the measurement or falsely detect a heart rhythm disturbance.
Why shouldn't you move during the measurement?
How does breathing affect blood pressure?
You should continue breathing at your normal rhythm while measuring your blood pressure to obtain realistic readings. The way you breathe can affect your blood pressure. Breathing exercises can therefore be used to treat high blood pressure. Deep, calm breathing can lower blood pressure - even during the brief period when it is being measured. In contrast, breathing rapidly, shallowly, or forcefully can cause your blood pressure to rise. Although you may be able to cheat a little this way to see lower readings on the display, you should be aware that these readings do not reflect your actual blood pressure. Therefore, please continue breathing normally while measuring your blood pressure.
Why not measure immediately after eating?
Why shouldn't you smoke before measuring your blood pressure?
Information about the longer-term effects on blood pressure can be found in our article „Why does smoking raise blood pressure?“.
Does drinking coffee or tea beforehand affect the measurement?
About half an hour before the measurement, you should not drink coffee or black or green tea. The caffeine (in coffee) or theobromine (in black and green tea) can raise blood pressure. The increase in blood pressure can be up to 20 mmHg, depending on the individual. This mainly affects people who consume these beverages only occasionally. People who regularly drink coffee or black or green tea often develop a tolerance. However, this also varies from person to person and may be slight. Therefore, blood pressure should be measured no earlier than 30 minutes after a cup of coffee or tea.
Why shouldn't you measure after drinking alcohol?
Why shouldn't you measure your blood pressure with a full bladder?
A full bladder is also a stress factor. During the filling phase of the bladder the sympathetic nervous system is activated. This brings the body into a higher state of readiness but it also causes the blood vessels to constrict. This can raise blood pressure.
So: If your bladder is full, go to the toilet first and then measure your blood pressure completely relaxed.
So: If your bladder is full, go to the toilet first and then measure your blood pressure completely relaxed.
Why shouldn't you take a bath before the measurement?
A warm or even hot bath in a bathtub causes blood pressure to fall. The warm water helps the body relax. The blood vessels dilate, and blood pressure goes down. The water pressure, however, helps blood return to the heart. Through hormonal regulation, this stimulates the excretion of fluid via the kidneys, which also helps blood pressure return to normal. If taken regularly, baths can have a relaxing effect that may also help lower blood pressure in the longer term. For this reason, a warm bath is not recommended shortly before a measurement, as the measurement should reflect everyday values.
Why does the ambient temperature matter?
Blood pressure measurements should therefore, whenever possible, be taken in rooms with a normal temperature.
Why shouldn't you take two measurements immediately one after the other?
When measuring blood pressure, the artery in the arm is compressed by inflating the cuff until briefly no blood flows through. As the air is slowly released from the cuff, increasingly more blood flows through the vessel again, which allows the blood pressure to be measured. After the measurement, the vessel is fully open again and blood can flow through freely. Nevertheless, you should wait one to two minutes between two measurements to make sure the vessel has returned to its normal width and the resting state has been reached. According to guidelines, two measurements should be taken one to two minutes apart.
Sources
- https://www.ncbi.nlm.nih.gov/pubmed/16231755
- https://www.aerztezeitung.de/Medizin/Verfaelschte-Blutdruck-Werte-275577.html
- https://www.herzstiftung.de/Kaffee-Blutdruck.html
- http://flexikon.doccheck.com/de/Sympathikus
- https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/2824754?guestAccessKey=f167dda3-8cad-4f34-99ca-79865446c64f&utm_source=for_the_media&utm_medium=referral&utm_campaign=ftm_links&utm_content=tfl&utm_term=100724
This article is from Tensana – the leading app since 2011, helping hundreds of thousands of people monitor their blood pressure every day.
Our content is based on carefully researched, evidence-based data and is continuously updated (as of 11/2025).
Author Sabine Croci is a qualified medical assistant with many years of experience in internal medicine and cardiology practices as well as outpatient care, and has headed the specialist editorial team at Tensana since 2015. Thanks to her extensive additional qualifications as an emergency medical technician, first responder, and in various areas of therapy and emergency care, she provides well-founded, practical, and reliably verified information.
Author Sabine Croci is a qualified medical assistant with many years of experience in internal medicine and cardiology practices as well as outpatient care, and has headed the specialist editorial team at Tensana since 2015. Thanks to her extensive additional qualifications as an emergency medical technician, first responder, and in various areas of therapy and emergency care, she provides well-founded, practical, and reliably verified information.
We hope you found the article helpful. Accurate measurements are essential for good blood pressure control. Our app Tensana can help with that. Clear instructions walk you through taking measurements according to current guidelines.
The app can also remind you if you wish. These features are fully available in the free version as well. Get the free app now.
