No matter how carefully you use any type of sphygmomanometer (blood pressure cuff), if your device isn’t calibrated, you’re going to get an incorrect reading. The most commonly-used manual blood pressure cuff by medical professionals, the aneroid sphygmomanometer, might even appear to be “zeroed” or calibrated but in actuality may be giving wrong numbers.
Even digital sphygmomanometers with their self-calibrating functions may not be calibrated correctly. We’re going to talk about why proper calibration of your blood pressure cuff is essential to an accurate diagnosis and give you some tips on how to calibrate your devices, both aneroid and digital.
Why Calibrating Your Blood Pressure Cuff Is Important
Even if you have one of the best sphygmomanometers, it still needs to be calibrated. Because an incorrect blood pressure reading can lead to an incorrect diagnosis. Taking a patient’s blood pressure is often the first thing a nurse or doctor does when they’re examining a patient. It’s become so routine that even patients expect it. When something becomes routine, it can go on autopilot, and you’re working on autopilot, it may be more difficult to notice a little thing like an inaccurate blood pressure reading from your sphygmomanometer.
Hypertension (high blood pressure) affects just under half of men (47%) and women (43%) in the U.S. today. So healthcare professionals aren’t surprised when a patient’s blood pressure is in the high range at or above 130/80 mmHg. Many nurses or doctors wouldn’t even blink at a high blood pressure reading. But what if the reading is off and the patient doesn’t actually have high blood pressure?
If your blood pressure cuff isn’t calibrated, a patient could potentially receive a misdiagnosis and be prescribed treatments and mediation they don’t need and could have a negative impact on their health. So you know how important calibration is – how do you know when your sphygmomanometer is out of calibration?
How To Tell If Your Blood Pressure Cuff Isn’t Calibrated
Aneroid sphygmomanometers are the most commonly used type of blood pressure cuff by healthcare professionals and the general public alike. They work by using a spring mechanism, gears, and a metal diaphragm to measure the pressure changes against the air bladder in the arm cuff. That’s a lot of moving parts and are prone to get knocked out of calibration or being worn out.
But there is an easy way to check to see if it’s out of whack – looking to see if it’s “zeroed”. At the bottom of the dial, the gauge is an oval marking. That represents zero. When the air bladder is fully deflated, the needle should point directly through the middle of this oval. If it’s outside of the oval, either higher or lower (usually higher) it means you aren’t zeroed and are getting incorrect readings.
HOWEVER: While this is a quick way to see if your aneroid blood pressure cuff is off, it isn’t 100% percent accurate. Even if the needle is in the oval, it could still be off. That’s why you need to test your aneroid sphygmomanometer against a reference standard – a manometer of known accuracy, usually a mercury sphygmomanometer.
Digital blood pressure cuffs are a bit different in that they have internal diagnostic programs to calibrate themselves. Most models have an alert or alarm to let you know that you need to run the calibration program.
Does the self-check feature of a digital blood pressure cuff make it better or more accurate than an aneroid model – you can find out here which is more accurate, manual or digital BP cuff? Not necessarily – they both still need to be regularly calibrated.
How To Calibrate A Manual Blood Pressure Cuff
There are three general ways to calibrate an aneroid blood pressure cuff that range from quick zeroing to sending the sphygmomanometer to an accredited lab. While sending your equipment to an accredited testing lab is by far the best way to ensure your sphygmomanometer is properly calibrated, it isn’t necessarily practical for the busy working healthcare professional.
1. Zeroing + Check
This is the quick and easy way to check the calibration of your aneroid sphygmomanometer.
If the needle of your dial gauge isn’t pointing directly through the oval at the bottom when the bladder is fully deflated, you need to zero it. Here’s how you do it.
- First, make sure the bladder is fully deflated when you check the position of the needle on the gauge. To be 100% sure, you can unhook the air hose from the bladder.
- Next, you need to return the needle to zero. You can do this by taking a pair of pliers and turning the nozzle on the dial gauge. If you prefer, you can remove the rubber tubing, but it’s not always necessary. The nozzle rotates and moves the needle either up or down. You want to move the needle until it’s pointing through the oval at the bottom.
- Lastly, when you’ve zeroed it, take a blood pressure reading and record the numbers. Then, using a manometer of known accuracy, most likely a mercury sphygmomanometer, take the blood pressure reading again. Compare the two numbers. Repeat until you have three readings from each device to see whether or not your aneroid blood pressure cuff is getting an accurate reading – it should be within 3 – 4 mmHg of the mercury sphygmomanometer.
2. Using A Y Test Kit
This method is more accurate. A Y test kit can be purchased online. It’s a tube with two extensions and a pump bulb – hence the Y name. One of the Y tubes attaches to a mercury sphygmomanometer and the dial gauge with the aneroid sphygmomanometer. You then pump the bulb and check the dial gauge against the mercury column.
- Remove the rubber tubing from the aneroid dial gauge.
- Check to make sure it’s zeroed. If it isn’t, follow the zeroing instructions above
- Attach the dial gauge to the proper tube
- Attach the other tube to the mercury sphygmomanometer of known accuracy
- Pump the bulb to a given pressure
- Check the aneroid gauge against the mercury column
- Make adjustments with the zeroing nozzle if necessary
- When the unit is fully deflated, the needle at zero should be within 3 – 4 mmHg of the mercury column reading
3. Send It To A Test Lab
Sending your aneroid blood pressure cuff to an accredited testing lab is the most reliable and accurate way to calibrate your equipment. Maybe not as practical, but if you absolutely need your blood pressure cuff to be as accurate as possible, it’s the best way.
How To Calibrate A Digital Blood Pressure Cuff
Most digital blood pressure cuffs have self-diagnostic programs that run when the unit is starting up. If it recognizes that it’s out of calibration, an alert or alarm sounds and asks you to run the calibration program. You can also run the calibration at any time you just want to check the unit’s accuracy. To further test the accuracy, you can check your digital blood pressure cuff against a manometer of known accuracy using the steps listed above for the aneroid sphygmomanometer.
- Turn on the digital blood pressure cuff. Follow the instructions and run the calibration program
- When it’s finished, take a blood pressure reading
- Then, take a blood pressure reading with a mercury sphygmomanometer of known accuracy
- Record both numbers and take at least 3 readings each
Both aneroid and digital sphygmomanometers need to be regularly calibrated and checked against manometers of known accuracy. The health and safety of patients rely upon accurate testing devices. But in addition to proper calibration, you need to know how to clean and care for a BP cuff.
How Often Should You Calibrate Your Blood Pressure Cuff
Depending on which source you refer to, the suggestions of how often you should calibrate an aneroid sphygmomanometer range from every six months to every two years. All types of blood pressure cuffs should be calibrated at least yearly, even mercury sphygmomanometer. But for aneroid sphygmomanometers, the general recommendation is every 6 months. This is also a good standard for digital models as well – rather than just relying on the self-diagnostic tools.
We have gone to the heart of the manner and detail how you can calibrate your aneroid and digital sphygmomanometers. Keep your blood pressure cuff clean, maintained, and calibrated to keep your patients healthy, safe, and happy.