I was prescribed a medication which can increase blood pressure as a side effect, so I impulsively bought a small home BP measurement unit of the foolproof kind. It is made by a known brand for home medical electronics, so I think it's of reasonable quality. I've never operated one before, although I've had it used on me.

After extensive RTFM, I used it several times over two days, and I frequently got weirdly low measurements. Diastolic was mostly between 50 and 60, but a few times, I saw the display drop to 30, then turn off and give an error. Right now, half an hour after the medicine, diastolic was 63, but systolic was only 90.

Seeing that I usually have a BP in the middle of the healthy range (when measured by somebody who presumably knows what he's doing), and I don't feel close to fainting, I assume that I'm doing something wrong when measuring. I tried doing everything right - sitting straight in a chair, cuff on the naked left arm at heart height, not moving for a while. What are the possible error sources left? Could I be making the cuff too tight or too loose? I am velcroing it at a width which feels similar to a long-sleeve undershirt.

  • <Comment deleted.> Please do not answer in comments. An actual answer, though, with references, is always greatly appreciated. Aug 8, 2015 at 15:08
  • 30 minutes after your meds probably means they haven't even taken effect yet. Why do you think the numbers like 90/63 that you got are incorrect? What would you expect without the meds and a pro taking the BP?
    – Carey Gregory
    Aug 9, 2015 at 5:40
  • It's ok to name the model. I'd be interested in seeing which sensing mode it uses. There are any number of reasons that a cuff might not sense accurately, from placement on arm to tightness of wrap.
    – JohnP
    Aug 11, 2015 at 22:17
  • @CareyGregory in all my readings done by a professional, my systolic was in the 100 to 120 range. I've had 63 for diastolic before, but that's slightly on the low side for me. The meds were prednisolone, and AFAIK hormones act quickly.
    – rumtscho
    Aug 16, 2015 at 11:31
  • @JohnP it is a Medisana BU 510. I was hoping that there is a very short list of things a patient should check for when getting implausible readings, regardless of model.
    – rumtscho
    Aug 16, 2015 at 11:33

1 Answer 1


The easiest way to find out what might be wrong is to take the apparatus to a healthcare practitioner's office with you, and have your BP measured by someone trained to do so correctly, then use the cuff, and see how closely they match. Then adjust the looseness/tightness of the cuff, the position, etc., until you get matching BP's consistently.

Accurate BP measurements depend on a number of things, but one that is really important is the rate at which the cuff deflates. If it deflates too quickly, it will give you falsely low BP's, in addition to BP's "all over the place" (some accurate, some not, some with a normal systolic pressure, but an abnormal diastolic pressure, etc.

If you can't find out what's wrong by correlating with manual BP readings, the apparatus is unreliable, therefore worthless.

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