I'd read your thread (well to be truthful galloped through it) and increasingly wondered with your 20 yrs background as T1 that maybe a refresh overall might help.
I noted that you had already touched upon prebolus timings; many (most?) of us find with Novarapid our natural insulin resistance is higher at the start of a day and decreases as the day goes on. That insulin resistance is often increased if our starting BG is already highish. This is one influence for prebolus time. We're trying to get our insulin to arrive into our blood stream at about the same time digested food is releasing glucose from that digestion into our blood. Now, of course another influence for prebolus time is whether the meal eaten digests rapidly or is slowed down by its fat content. Before getting you bogged down in this potentially daunting complexity, I'd like to go a couple of steps back into some useful generalities about estimating bolus.
There has been a very recent post and responses when
@MarcR asked about "Insulin Calculation". He was actually asking about bolus insulin. A longstanding T1 forum member,
@helli, provided a short but extremely useful summary with her perspective on this quandary. I quickly did a cut and paste of that reply into my D notepad and I'm pasting that here, more or less verbatim, just with tiny formatting differences for my notepad. My italics.
There are a number of factors involved with insulin dose calculation:
1. starting BG.
2. insulin sensitivity - by how much does 1 unit of insulin reduce your BG?
3. insulin to carb ratio - how many grams of carbs do you need for 1 unit of insulin?
4. plans - are you about to do something that needs more (e.g. stressful) or less (e.g. cardio exercise) insulin?
5. insulin on board - do you have any active fast acting insulin in your body?
6. insulin to protein ratio - if we eat a low carb meal, we also need to consider the protein. But this part of the bolus is typically taken later.
All these points differ from person to person.
Basal is the "insulin foundation". Just like a house, if your foundation is wrong, you are building on an unstable base.
Age of diagnosis is irrelevant in terms of dosage and number of units of insulin is very personal. For some people 10 -12 units is a lot. For some people it is low. Maybe they have not been taught to carb count - some people are advised to take fixed doses, for various reasons do not adjust their dose according to what they eat.
It has been mentioned a few times - they need to talk to the professional who looks after their diabetes care such as a DSN.
You might well find these points a useful starting point, then perhaps ask questions for any of these points that need amplifying from generic into actual examples. I firmly subscribe to the principle that getting your basal right first is essential. If my basal has drifted out of kilter (and things do naturally change with diabetes) then my bolus dosing frequently doesn't do what I was expecting.
Have you come across Gary Scheiner's book "Think Like a Pancreas"? I found his relaxed style of writing very easy to get along with and although he is from the USA he puts in many examples and always gives our European numbers as well as in the American units. He is T1 himself and a practicing sports diabetes therapist.
