@steveo4
There’s a lot of other info to consider before deciding to correct a reading of 18,
@DunePlodder has rightly said that we don’t know your correction ratio, when did you last eat, what’s your bolus ratio, also why have your levels hit 18, are you unwell, do you need to check your ketones, is there any issue with your insulin. Who has told you to still correct whilst you already have 4 units on board ?
It’s not a simple yes/no answer and getting it wrong means hypo.
Personally I would take into consideration many factors before hitting the bolus and knowing my body as well as I do now I am comfortable making that decision for myself without anyone else trying to do it for me, hopefully your levels have come down now but if your not ok making the call yourself then it’s a good idea to really learn and get to grips with your correction ratios so you are ok managing this for yourself.