Not measurable...way off the charts maybe? Not sure as I am not a medical professional.
A 210 blood sugar reading is too high a reading two hours after a meal. It should be 140 or under.
I, for one, need to reduce my intake of carbs drastically. My body is "allergic" to carbs, any kind of carbs. We are all different, but some of us react to any kind of carb we eat with a higher blood sugar.
Your husband's A1C is way off the charts, as you said. An A1C of 18 averages about 470 blood glucose reading daily for three months. That is dangerous. He needs to get it down as fast as possible.
He needs to see an endocrinologist. The emergency room is not in order at the moment unless his blood sugar rises to around 500. Then he needs to get it down immediately.
My A1C was 13.2. The dietician suggested 35-45 carbs per meal. I stick to the lower number and even then I only eat 20 or so carbs per meal. For many of us, 150 grams of carbs per day is too much. That averages to 50 per meal, which can be too much for someone like your husband. Seeing you husband's numbers, I believe he should cut down his carb intake further. This may help until he sees the dietician.
When he sees the dietician, it should be mentioned that his numbers are always high.
It does take awhile for the body to adjust to lower numbers, especially since his have been running high.
Metformin takes awhile to kick in before you see any reduction in numbers. To the right of this forum you will see an expert column written by Dr. Dansinger. Have your husband take a look. It is very informative.
I use two insulins to keep my diabetes under control. My doctor did not think oral medications would be beneficial. My last A1C was taken this past Thursday - 5.8, a far cry from my very first one.
I don't know what type of insulin was administered to your husband. There are many types in which actions start immediately, such as Humalog (10 minutes after injection.) Others take longer to make its effects known.
I think it best your husband start to lower his intake of carbs. If he can, exercise should be done at least 7 1/2 hours per week (Dr. Dansinger's suggestion.) Drink plenty of water. Take his medication at the same time every day. If none of this works, it is time to re-evaluate his therabpy.
I was labeled an "uncontrolled diabetic." When insulin therapy was begun, I was to journal the food I ate at every meal, the amount of carbs in that food. I was to take my blood sugar before eating and then two hours after. This was for every meal. Anything I put in my mouth needed to be documented. I did this for two weeks and then I was re-evaluated. It was extremely helpful to see everything in black and white.
As I stated before, there is not need for the ER unless his sugars are extremely high. I know he's feeling badly at the moment. Did he eat something high in carbs that would cause his sugar to rise rapidly and then fall rapidly? Sometimes that can happen.
This is the weekend. It tends to be slow on the forums. Hopefully, others will come along with more advice.