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. Its well known that measurements should be taken at rest both physically and mentally while sitting or lying down. Its also easy to understand that you should measure before taking your medication. Only then are values comparable.
But why shouldnt you speak during the measurement? How can breathing influence the process and why shouldnt you smoke beforehand? What happens if, when using 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 pulsing blood when the cuff is inflated and released. The blood pressure is then calculated from these signals. If there is a thick sweater, a jacket, or folds of fabric (for example from wide sleeves) between the sensor and the artery, the sensor can no longer detect those vibrations and the measurement can be wrong.
Therefore, you should free the arm for the measurement. Only very thin, tight-fitting sleeves may possibly be left on.
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 sleeve can distort the result. Rolling or pushing up the sleeve can make it tighter or make narrow parts of the sleeve sit over thicker parts of the arm. If the arm is pinched or strongly compressed, a narrowing of the arteries occurs before the blood pressure cuff and the measurement can no longer give realistic results. Therefore only roll up or push up garments that are loose enough.
The correct cuff size is important!
The blood pressure cuff 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 it can be placed two to three centimeters above the elbow crease. In length the cuff must fit well around your upper arm. Many cuffs have a mark that shows whether the cuff fits. Often another mark helps you find the correct position so that the sensor sits over the artery and can record the pulses. A cuff that is too wide or too short can sometimes give falsely high readings. If in doubt, measure your upper-arm or wrist circumference before buying a device and take that into account.
What happens if the measurement point is too high or too low?
Why shouldnt you speak during the measurement?
Talking is a form of exertion that can raise blood pressure. The body is then not at rest. In addition, speaking can disturb the device during the measurement and cause it to stop or to falsely register a heart rhythm disturbance.
Why shouldnt you move during the measurement?
How does breathing affect blood pressure?
You should continue to breathe in your normal rhythm during the blood pressure measurement to get realistic values. The way you breathe can influence blood pressure. That is why breathing exercises can be used in the treatment of high blood pressure. Deep, calm breathing can lower blood pressure even during the short measurement period. If you breathe quickly, shallowly, or with forced breathing, blood pressure can rise. Although you might be able to cheat a little to see a lower value on the display this way, be aware that those values wont reflect your actual blood pressure. So please breathe normally while you measure.
Why not measure immediately after eating?
Why shouldnt 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 (coffee) or theobromine (black and green tea) can raise blood pressure. Individual increases can be up to 20 mmHg. This mainly affects people who only drink these beverages occasionally. Regular coffee or black/green tea drinkers often develop a tolerance. This is also individually different and can be small. Therefore measure blood pressure no earlier than 30 minutes after a cup of coffee or tea.
Why shouldnt you measure after drinking alcohol?
Why shouldnt you measure 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 shouldnt you take a bath before measuring?
A warm or hot full bath makes the blood pressure fall. The warm water relaxes the body. The blood vessels dilate and blood pressure goes down. The water pressure also supports blood return to the heart. This stimulates hormonal controls that increase fluid excretion via the kidneys and thus helps normalize blood pressure. This relaxing effect can help lower blood pressure in the long term if baths are taken regularly. For a measurement taken shortly afterwards, however, a warm bath is not recommended because the measurement should reflect everyday values.
Why does the ambient temperature matter?
Blood pressure measurements should therefore be taken in rooms with a normal temperature.
Why shouldnt 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, blood starts to flow through the vessel again, which allows the blood pressure to be measured. After the measurement the vessel is fully open and blood can flow freely again. Still, 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 is 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 comes from BloodPressureDB – the leading app since 2011 that helps hundreds of thousands 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 in outpatient care, and has led BloodPressureDB's specialist editorial team since 2015. Thanks to her extensive additional qualifications as a paramedic, first responder and in various therapy and emergency areas, she provides solid, practical and reliably reviewed information.
Author Sabine Croci is a qualified medical assistant with many years of experience in internal medicine and cardiology practices as well as in outpatient care, and has led BloodPressureDB's specialist editorial team since 2015. Thanks to her extensive additional qualifications as a paramedic, first responder and in various therapy and emergency areas, she provides solid, practical and reliably reviewed information.
We hope you found the article helpful. Accurate measurements are essential for good blood pressure control. Our app BloodPressureDB can help with that. Clear instructions walk you through taking measurements according to current guidelines.
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