Wrist blood pressure monitors are frequently criticized for inaccurate readings. Some of these readings are not the fault of the wrist monitor but because of some other reason. Therefore, let’s find out the answer to, why do wrist blood pressure monitors give higher or lower readings?
A wrist blood pressure monitor can give higher or lower readings for the following reasons:
- The cuff is above or below heart level
- The cuff is too tight or loose
- The cuff size is incorrect
- The cuff is positioned improperly
- The wrist or hand is unrelaxed
- The wrist is bent
- The arm or body is unsupported
In this blog post I’ll explain how each one of the above reasons can be easily corrected. Once the correct way to measure your blood pressure with a wrist cuff is learned, your measurements will become more accurate. Therefore, let’s dive right in and start learning your true BP!
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The Wrist Cuff is Above or Below Heart Level
The wrist cuff must be at the same level of the heart to achieve an accurate reading. If the wrist cuff is above heart level, the measurement can be lower. If the wrist cuff is below heart level, the measurement can be higher.
The reason for this is hydrostatic pressure 1 which is how much pressure is exerted by fluid because of gravity. This plays a role in your blood pressure measurements 2. This is explained in much more detail in my blog post, Why Does Your Arm Have to be at Heart Level When Taking BP?
How do you achieve heart level with a wrist cuff?
- Sit in an upright chair with your back supported and feet flat on the floor.
- Rest the elbow on a flat, comfortable surface.
- Raise your wrist until the cuff is at the same level of your heart.
Some wrist monitors have a heart level indicator like the Omron Gold Series. Check out my detailed review on it here, Omron Gold Wrist Blood Pressure Monitor Review.
Studies have shown differences when the arm is not at heart height. In the book, In Hypertension Primer: The Essentials of High Blood Pressure, it states a BP reading will be falsely low by 0.08 mmHg for every 1cm the arm is above the heart 3.
A study involved 240 people with high blood pressure. Their measurements were taken with their arms in various positions. When their arms were held straight down compared to at heart height, the measurements were 8 mmHg higher 4.
The Cuff is Too Tight or Loose
It’s possible to have a wrist cuff too tight or loose. If it’s too tight, you may have a higher measurement. If the cuff is too loose, you may have a lower measurement 5.
How do you apply a wrist cuff so it’s not too tight or loose?
- Wrap the cuff around your wrist so there’s no space between the cuff and your skin.
- The cuff should be tight enough so two fingers can be inserted between the cuff and wrist.
- It you can’t slip a finger between the cuff and wrist, it’s too tight.
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The Wrist Cuff Size is Incorrect
This problem occurs more with an upper arm monitor than a wrist monitor. Even though, it’s still possible. It’s important to measure the circumference of your wrist and ensure the wrist cuff’s size range includes your wrist size.
How do you measure your wrist for a wrist blood pressure monitor?
- Wrap a cloth measuring tape evenly around the wrist just below where the bone protrudes out from the top of the wrist.
- Note the measurement and write it down with your BP records.
- Compare the wrist measurement to the size range of the wrist cuff.
- The wrist measurement shouldn’t be less or more than the size range of the wrist cuff.
The Wrist Cuff is Positioned Improperly
The positioning of the wrist cuff is just as important than having the correct size or tightness. The wrist cuff I own, the Omron Gold Series, (check it out on Amazon) states to position the top edge of the wrist cuff approximately 1/2″ from the wrist crease 6.
Once this is done, rotate your forearm around and ensure the cuff is not covering the protruding bone on the topside of your wrist. If it isn’t covering it, the cuff location is fine. If the cuff is covering the bone, slide it down until it’s just below the bone.
Once the positioning is correct, check the tightness of the cuff and make any adjustments if needed. After adjusting the tightness, recheck the cuff distance from the crease and the protruding bone.
The Wrist or Hand Is Unrelaxed
The wrist should remain relaxed and not clenched into a fist. A clenched fist tenses your forearm muscles and can affect the blood pressure reading. It’s important to remain calm and relaxed five minutes prior to the reading and during the reading.
It’s important to note while relaxing the wrist, it should not be bent forward or backwards during the measurement. This leads me to the next topic, bending the wrist.
The Wrist Is Bent
In addition to relaxing your wrist and hand do not bend your wrist forward or backward. If the wrist is in one these positions, you’re likely tensing one of your forearm muscles.
The Arm or Body is Unsupported
The arm should be supported when measuring your blood pressure with the wrist monitor. This is accomplished by placing the elbow on a comfortable, flat surface.
In addition, the body should be supported by sitting in an upright chair, feet flat on the floor, back supported and legs uncrossed.
Too many people measure their blood pressure with a wrist cuff while standing and placing their wrist and arm against their torso. This position doesn’t relax the body and tenses some muscles which can cause the measurement to be higher.
Read Next – More Wrist Monitor Articles
- Dictionary.com: Hydrostatic pressure
- National Center for Biotechnology: Blood pressure measurement
- Google books: Hypertension Primer: The Essentials of High Blood Pressure Chapter C109 Blood Pressure Measurement
- National Center for Biotechnology Information: Effects of Arm Position and Support on Blood-Pressure Readings
- Hypertension: 2017 ACC/AHA/AAPA/ABC/ACPM/AGS/APhA/ASH/ASPC/NMA/PCNA Guideline for the Prevention, Detection, Evaluation, and Management of High Blood Pressure in Adults: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines
- Omron: FAQs: Blood Pressure Monitors