So it's a one time thing? Meaning, just this evening? Is he symptomatic? If he's feeling dizzy or lightheaded, having chest pains, those are issues. But having a low diastolic for one evening could be fine. And he's pre-hypertensive according to those systolic numbers, but again, one reading doesn't say everything. Re: blood pressure alone. Measure it at the same time for a few days if you continue to worry. That'll give you a picture of what his bp is overall. Re: tonight. If he's having other symptoms, act on those.