This could potentially be malignant hypertension
which needs urgent medical management- if this reading is correct of course. Take your dad to the hospital or he must see his Doctor today. Do not leave it.
You don't mention his age or whether or not he usually suffers from high blood pressure
, what other medical conditions he has or if he is taking any BP medication?
But none the less, malignant hypertension is a syndrome which we characterise by severe hypertension
(e.g. systolic >200 and/or diastolic >130 mmHg) accompanied by nephropathy, or by papilloedema.
Even accelerated hypertension
or acutely elevated blood pressure can be indicative of haemorrhages. These more serious issues needs to be excluded.
Just to clarify. At this stage we cannot determine why his reading is high (or if indeed it really is that high), you must get your father evaluated today. It may not be an indication of anything serious but to be on the safe side, your father must see a Doctor today.