Thanks for the tag,
@Jaylee .
@RichardSp8 , you've asked about it being erratic. It comes with the territory but as time goes by you'll learn skills to make it less so.
The main problem is that, although there's some basic rules, for example 1 u for each 10 g (that can vary a lot too, often within the same person at different times of day), as soon as you inject and eat food, they are subject to a whole lot of bodily processes which can throw the calculations out.
In a non-T1, most insulin goes straight to the liver to tell it to suck up excess glucose. Our injected insulin tends to get nowhere near the liver, and some of it will be destroyed by insulin antagonists before it does anything. There's some work being done on adding, " hepatic directed vesicles" to insulin, which taxis insulin straight to the liver so that it more closely emulates normal insulin function, so that might be a new toy to play with in the next few years.
So, it's always going to have a degree of uncertainty to it.
One useful way of dealing with it is to understand how insulin operates over time. It has a pattern, not sure what humalog looks like, there's no doubt a graph on the internet, but my novorapid, for example, takes about 20 mins to get to work, peaks after about an hour or hour and a half, and works at a declining rate for about 3 to 5 hours.
Knowing that, it means that I can take a shot about 20 mins before a meal, so that it'll already be working when the food hits it, instead of playing catch it, and then I'll know about the hour mark whether I've got it right or under or over bolused. I'll also know that if I'm going to be doing some exercise later on within the 3 to 5 hour window, I'll still have some active insulin on board, and that might lower me a lot if I'm exercising because things called glut4 transporters in each of my cells will be stimulated by exercise and lower bg.
Once those basic mechanisms are understood, it lets you then think about tweaking doses and timing. For example, if I'm having a Thai green curry, white rice, with me, at least, gets absorbed fairly quickly, so I'll pre-bolus about 20 mins, but if it's brown rice, it's absorbed more slowly, so 20 mins would make me hypo, so 10 mins would do. Or, if I know I'm going to be sitting in the office after lunch, it'll be x units, whereas if I'm on holiday and know I'm going to be spending a few hours walking around sightseeing, I'll know that'll bring glut4 into play, so I'll likely shave quite a few units off to avoid the insulin and glut4 doubling up. Or I might leave it at the same amount as I often holiday in Krakow and there's always a quality ice cream parlour at hand! I might also shave off or add a few units if my levels are on a downward or upwards trend at the time of the shot
I suppose the point I'm trying to make is that just looking at the number of carbs when carb counting is too simplistic. We have to consider the surrounding circumstances too, in terms of type of food, what's happened in the last few hours, and what might happen in the next few hours.
One of the big things happening in the UK at the moment is freestyle libre starting to become available on the nhs. It's still very much a postcode lottery at the moment. Some areas are very liberal with it, but most are not - google your area's health authority and there will likely be a policy statement on it. Strips just give you a snapshot in time, which is of limited use when you're dealing with a constantly moving target. But then you've got cgm - continuous glucose monitoring. It makes it a much fairer game when you can actually see what you're dealing with. Formal nhs education is not keeping up . It's based on strips. Official carb counting courses like DAFNE will say things like don't test between meals unless you feel hypo and save corrections until meals. Sorry, f*ck that. With cgm, if I see my graph starting to inflect up or down, I can decide on the fly whether I need a small 5g or 1 or 2u correction to tweak it back imto line before it gets anywhere near out of range. It removes a lot of the uncertainty and erraticness. Plus your phone will ring if you go below a set point, so you can avoid hypos.
Cgm is hugely liberating and I'd strongly encourage you to look into it. There's dexcom, officially costs £200 per month, but there's ways of using it unofficially which bring it down to about £100 per month. Libre is £100 per month, and there's a small add on transmitter called blucon for £96 one off cost which turns it into cgm. If you live in an area which does libre on the nhs, all the better - cgm for free.
Some good books:
Think Like a Pancreas - Gary Scheiner
Sugar Surfing - Stephen Ponder
Beyond Fingersticks - William Lee Dubois
Breakthrough... - Thea Cooper
The middle two are about cgm. The last one won't teach you much about the management of T1, but it's still worth a read. Well researched book about the history of the discovery of insulin. The stories about parents queuing up around the block in the desperate hope of getting some of the limited supplies are harrowing. We're not lucky to be T1, but we've got it relatively easy compared to back then.
Good luck, mate, this is often not an easy ride, but it's do-able. Once you get the basic rules under your belt, you'll be surprised how much latitude there is. And if it all goes wrong, there's nothing a bag of jelly babies won't sort!