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Deciding How Much Insulin to Take?



I`m a type 2 diabetic. I take novalog 3 times a day and lantus at bedtime. My a1c test is 5.2. What I want to know is how much insulin to take befor meals and at bedtime. Right now I`m guessing at how much insulin to take. My Dr. said I`m doing fine with what I`m doing. Sometimes I take to much insulin or not enough. Is there a guide line you can kind of follow to determine how much insulin to take?


First of all, congratulations on achieving a HbA1c of 5.2! You must be working hard on your diabetes care. It is great that you want to control your blood glucose levels, and are seeking information to learn more about it. 

Some people need only a basal insulin and some need only a “bolus” insulin taken with meals.  It sounds like your doctor felt that you needed both.  Lantus (insulin glargine) is one example of a basal or “base” insulin, others being NPH insulin or Levemir (insulin detemir).   Everyone with type 1 diabetes and some people with type 2 diabetes need basal insulin, 24 hours a day, regardless of eating. The dose of basal insulin does not usually change often, and the dose is not related to the amount of food you eat. The dose of basal insulin is adjusted by studying blood glucose readings, in particular watching what happens from the time you go to bed until the time you get up in the morning. Your doctor or diabetes educator should help you to learn how to adjust your basal insulin dose.

There are several forms of rapid acting insulin:  Humalog (insulin lispro), Novolog (insulin aspart), and Apidra (insulin glulisine) are considered ultra-short acting insulins while regular insulin (available as Humulin and Novolin in the United States) is considered short acting but not as short as the ultra-short insulins.  A rapid-acting insulin is taken to match carbohydrates and to correct high blood glucose levels. First you need to learn how to count carbohydrates in your diet. Careful carbohydrate counting is essential in maintaining steady blood glucose levels.

The dose of rapid-acting insulin taken to match the carbohydrates eaten will vary from dose to dose. For example, if you eat 60 grams of carbohydrate you would take more rapid-acting insulin than if you ate only 30 grams of carbohydrate. Your diabetes care provider should give you a “carbohydrate ratio” to help you calculate the dose of insulin. For example, if your carbohydrate ratio is 12 – then you would take one unit of insulin for every 12 grams of carbohydrate eaten. If you ate 60 grams of carbohydrate, you would take 60 divided by 12 = 5 units of insulin.

Rapid-acting insulin is also taken to lower high blood glucose levels. You can calculate how much insulin you need to take to lower a high blood glucose level if you know your “correction target” and “sensitivity factor”.

The correction target is the top end of your blood glucose goal. For example, if your blood glucose goal is 70-140 mg/dl, then your correction target is 140 mg/dl.

Your sensitivity factor is equal to how far one unit of rapid-acting insulin will drop your blood glucose level. For example, if one unit of insulin drops your blood glucose by 40 mg/dl – then your sensitivity factor = 40.

To calculate your correction dose, you start with figuring out how much you need your blood glucose to drop to reach your target. For example: if your blood glucose is 228 – the first thing you do is take 228 minus your target of 140 = 88. Therefore you want your blood glucose to drop 88 mg/dl to reach the target.

Next you need to calculate how much insulin is needed to lower your blood glucose 88 mg/dl. To continue our example – if you want your blood glucose to drop 88 mg/dl, and for example your sensitivity factor is 40 – then you take 88 divided by 40 = 2.2 units of insulin. If you take 2.2 units of insulin (most people would round this to 2 units unless on an insulin pump), the 228 mg/dl glucose should drop close to your target of 140 mg/dl.

VERY IMPORTANTThe examples used above are only examples – you need to talk to your diabetes care provider to obtain the correct basal insulin dose, carbohydrate ratio, correction target, and sensitivity factor for you. Every person is different – so each person needs their own instructions for calculating insulin doses. Once you are comfortable with the calculations, your diabetes care provider should teach you how to adjust your plan so you can make changes when needed.  This is considered the up to date approach to calculating insulin dose.  Some people use approaches which are not so mathematical.  The advantage of these approaches is that they give you more flexibility to take care of your own diabetes than if you are advised to take the same fixed dose under all circumstances.  For some people, there may be a reason to use a simpler approach.  This can be individualized be providers experienced in the care of diabetes.

You can find additional information on the American Diabetes Association website (see link below). Look under “Type 2 diabetes” and “insulin therapy”. In addition, they publish a booklet titled “Complete Guide to Carb Counting, 2nd edition” that has more detailed information. On the website, you can find the closest local chapter of the American Diabetes Association – they usually keep copies of their publications, and you could stop by and look at them to see if they are helpful, before purchasing them.

If you have not already seen a diabetes nurse educator and/or a diabetes dietitian – ask your diabetes care provider for a referral.  When making the appointment, be sure to specify you want to meet with someone to learn more about carbohydrate counting and taking insulin based on carbohydrates and blood glucose levels.

It is important that you work with your diabetes care provider to reach your diabetes health goals. But “self-management” is the key to good diabetes care. So keep asking questions and learning as much as you can about diabetes treatment. Good luck!

Related Resources:

American Diabetes Association

For more information:

Go to the Diabetes health topic.