The following is from Reference (1)
Purchase a good monitor and make sure it is reliable. The American Heart Association recommends purchasing a monitor that has been validated through the Association for the Advancement of Medical Instrumentation, British Hypertension Society or the International Protocol for the Validation of Automated BP Measuring Devices.
[You can] Send your monitor to a specialized company or check with the manufacturer of your blood pressure monitor. The manufacturer may have a factory where your device can be calibrated for you. There are also organizations that specialize in calibrating blood pressure monitors. This is usually reserved for monitors that are used in medical settings, as it is quite expensive.
The following is from Reference (2):
To monitor blood pressure effectively, your Omron blood pressure monitor must be properly calibrated by the Omron service center.
Determine whether it is time to recalibrate your Omron blood pressure monitor, which depends on how often you use your Omron monitor. Those that are used up to five times a day should be calibrated annually. For less use, every 3 to 5 years is recommended.
Call the Omron customer service number at 1-877-216-1333 during their service hours of 8:30 a.m. to 4:30 p.m. central time. An Omron representative will help you determine whether you have a valid warranty on your Omron monitor and if it will cover a calibration service. If your calibration service is not covered, the representative will tell you the current rate for the service and give you a customer service number.
I called the above Omron 800 service number and spoke with the service rep. She said that there was no charge for calibration check even if the machine is out of warranty. The customer pays postage to mail to service center. The center will check it for accuracy and if it is accurate they will mail it back to you at their expense. However, if it is out of warranty and out of calibration, they will not recalibrate it. Rather they will dispose of it and let you know that.
Reference (4) is actually somewhat reassuring. In this 2011 study, the authors evaluated for accuracy, almost six hundred blood pressure monitors used in British general practices Here are some excerpts:
Overall, 86% (503 of 584) of individual devices were within 3 mmHg of the standard across the pressure range (‘green’ classification), 13% (77 of 584) had one or more error of 4–9 mmHg (‘amber’), and <1% (4 of 584) had one or more error >10mmHg (‘red’). Significantly fewer mercury (4/75 [5%]) and digital devices (36/308 [12%]) failed the 3 mmHg standard than aneroid (41/191 [21%]) (Figure 1). Compared to mercury, digital devices were no more likely to fail the BHS standard (relative risk [RR] = 2.19, 95% confidence interval [CI] = 0.80 to 5.97), but aneroid models were four times more likely to fail (RR = 4.02, 95%, CI = 1.49 to 10.8). The 10 hybrid devices were all within 3 mmHg of the reference standard.
Device accuracy was similar between the most common manufacturers: all errors were within 3 mmHg in digital devices manufactured by A&D/boso or Omron in 89% (92/103) and 88% (173/196) of cases respectively, and 83% (5/6) of others (P = 0.7 for difference between manufacturers).
There were 17 apparently brand new devices. Of the remaining 567, 147 (26%) had been tested within the previous 6 months, 173 (31%) within the past 6 to 12 months, 97 (17%) had been tested more than 12 months ago, and 150 (26%) had no record of previous testing. Overall, no significant difference was found between testing date and accuracy of device: a ‘green’ rating (within 3 mmHg) was achieved in 87% (128/147) of devices tested in the last 6 months, 89% (154/173) of those tested within 6 to 12 months, 87% (84/97) of those tested over 12 months before, and 80% (120/150) of those never tested (P=0.1).
The accuracy of a device was not related to the size of practice (P = 0.7) or the holder of the device — whether this was a GP, practice nurse, or district nurse, or the device was on loan to a patient (P = 0.7).
This study shows that the most commonly used sphygmomanometers in UK primary care are now digital devices, which outnumber mercury models 4:1. Overall, one in seven devices failed the BHS standard requiring all devices to read within 0–3 mmHg of the true value. The performance of mercury and digital models was similar and significantly better than aneroid models. This difference appears to be explained by the presence of a group of donated aneroid sphygmomanometers with no discernible manufacturer No significant differences were seen between devices from the commonest manufacturers, nor between those used by different professional groups, which suggests a maturing of the underlying technology. There was little evidence that previous calibration made any difference to current accuracy, although just over half had been checked within the last year.
Reference (5 ) includes information on how to do a calibration check of a blood pressure monitor using the The CuffLink Non-invasive Blood Pressure Stimulator.
Finally, I spoke with Mr. Steve Erdosy of Community Biomedical and he had many helpful suggestions. He stated that the biomedical department calculates all the blood pressure cuffs in the Community Physicians offices once a year. He states that his clinical impression is that the automated blood pressure cuffs are more accurate that the aneroid ones. And he said that the hospital uses Welsh Allen monitors and he is very satisfied with them.
Mr. Erdosy stated that much of the inaccuracies that can occur with the automated blood cuff are due to misapplication of the cuff – for example the cuff is too lose, or the cuff is not applied correctly (the blood pressure cuff needs to be placed so that it can correclty sense the brachial artery), or the cuff itself is old.
(3) Which is More Accurate in Measuring the Blood Pressure? A Digital or an Aneroid Sphygmomanometer. [PubMed Abstract] [Full Text HTML] [Full Text PDF]. J Clin Diagn Res. 2016 Mar;10(3):LC11-4. doi: 10.7860/JCDR/2016/14351.7458. Epub 2016 Mar 1. (4) Type and accuracy of sphygmomanometers in primary care: a cross-sectional observational study. [PubMed Abstract] [Full Text HTML] [Full Text PDF]. Br J Gen Pract. 2011 Sep;61(590):e598-603. doi: 10.3399/bjgp11X593884. [This is an excellent article.]
(5) Blood Pressure MonitorRe-calibration – Final Report, BME 273 – Spring 2011. Vanderbilt University Medical Center.
(6) Accuracy of monitors used for blood pressure checks in English retail pharmacies: a cross-sectional observational study. [PubMed Abstract]. Br J Gen Pract. 2016 May;66(646):e309-14. doi: 10.3399/bjgp16X684769. Epub 2016 Mar 29. [For the study they used an Omron PA-350 as the calibrated reference device for evaluating the blood pressure machines in the pharmacy.]
(7) Determining which automatic digital blood pressure device performs adequately: a systematic review. [PubMed Abstract] [Full Text HTML] [Full Text PDF]. J Hum Hypertens. 2010 Jul;24(7):431-8. doi: 10.1038/jhh.2010.37. Epub 2010 Apr 8.
(8) Accuracy of ambulatory blood pressure monitors: a systematic review of validation studies. [PubMed Abstract] J Hypertens. 2013 Feb;31(2):239-50. doi: 10.1097/HJH.0b013e32835b8d8b.
(9) A novel and simple protocol for the validation of home blood pressure monitors in clinical practice [PubMed Abstract]. Blood Press Monit. 2012 Oct;17(5):210-3. doi: 10.1097/MBP.0b013e328356e196.