Basal testing

Are you taking too much basal insulin?

Doing a basal test is the best way to test if the basal insulin dose is right. It involves testing the glucose levels for a set period of time where the patient fasts and when only the basal insulin is working.

How does it help?

If the basal insulin dose is right, diabetes is much easier to manage. If the dose is too high, your patient will be having hypos and eating a lot more. If it is too low, your patient will be having high glucose levels and adding extra doses of rapid insulin to keep the glucose levels in range.

How is a basal test performed?

Doing a basal test involves fasting for a section of the day when only the basal insulin is working. After a meal, it takes 4 hours for the rapid-acting insulin (or a bolus in the pump) to wear off, so the basal test starts then. Your patient needs to check their glucose levels every 1 or 2 hours for the period (4 – 6 hours) and then decide if the basal insulin dose needs to be changed. If your glucose levels drop by more than 2 mmol/L, you know that the basal insulin dose is too high and needs to be decreased.

The different sections are:

Overnight: 10pm – 6am.
Morning: 6am – 12pm.
Afternoon: 12pm – 6pm.
Evening: 6pm – 12am.

It’s best to test one section per day and consider doing two tests before you decide to change the insulin dose. After you’ve made any change to the insulin dose, it’s a good idea to re-test each section of the day to make sure the changes to the dose improved the glucose levels.

How to prepare for the test

Start the test with a blood glucose of 4 – 10 mmol/L.
Make sure the last meal and dose of rapid insulin was at least 4 hours ago.
Cancel the test if your patient:
- Had a hypo (glucose less than 4) in the past 6 hours.
- Did some vigorous exercise in the past 12 hours.
- Drank alcohol in the past 12 hours.
- Have a significant stress or illness during the test.
If your patient is using an insulin pump, they should not do the basal test on the first or last day of the infusion set.

Patient Instructions for performing a basal test

Step 1: Eat your “last meal” and give your usual rapid insulin dose for it.
Step 2: Wait four (4) hours so that the rapid-insulin dose has worn off:
- Don’t eat anything after the time given – this is the start of your fast.
- Drink plenty of water, tea (without milk or sugar) or sugar-free fluids eg. soda water.
Step 3: Check your glucose level at the beginning of the testing interval:
- If it is 4.0 – 13.9mmol/L, continue the test.
- If it is below 4.0mmol/L, treat the hypo and cancel the test.
- If it is 14.0 or above, give a correction dose of rapid-acting insulin, and cancel the test.
Step 4: Check your glucose levels every 2 hours during the testing period:
- If your glucose level drops to below 4: Treat this and cancel the test. You have proven that your basal insulin dose is too high.
Step 5: You can eat your meal at the end-of-testing period. Yes, give your rapid insulin dose with it.
Step 6: Decide what to do with your basal insulin dose.

Step 7: Decide what to do with the dose of basal insulin:

Basal testing worksheet

(PDF for download and printing) see Appendix.

		Day 1	Day 2
	Date:
Finish eating	6pm
Last bolus dose or rapid-acting insulin	6pm
Blood glucose test	10pm
	12am
	2am
	4am
	6am
Difference between glucose levels at 10pm and 6am
Insulin dose plan

Glucose level	Interpretation	Suggested insulin dose change
? glucose within 2 mmol/L	Basal dose is perfect	No change to basal dose
? by more than 2 mmol/L	Basal insulin dose is too low	Increase dose by 10%
? by more than 2 mmol/L or glucose is below 4 mmol/L	Basal insulin dose is too high	Reduce dose by 10 - 20%

		Day 1	Day 2
	Date:
No more food after	2am
No bolus dose or rapid-acting insulin after this time	2am
Blood glucose test	6am
	7am
	8am
	9am
	10am
	11am
	12pm(noon)
Difference between glucose levels at 6am and 12pm (noon)
Plan for Basal Insulin Dose

Glucose level	Interpretation	Suggested insulin dose change
? glucose within 2 mmol/L	Basal dose is perfect	No change to basal dose
? by more than 2 mmol/L	Basal insulin dose is too low	Increase dose by 10%
? by more than 2 mmol/L	Basal insulin dose is too high	Reduce dose by 10 - 20%

		Day 1	Day 2
	Date:
No more food after	8am
No bolus dose or rapid-acting insulin after this time	8am
Blood glucose test	12pm
	1pm
	2pm
	3pm
	4pm
	5pm
	6pm
Difference between glucose levels at 12pm and 6pm
Plan for Basal Insulin Dose

Info for Medical Professionals

Basal testing

Patient Instructions for performing a basal test

Basal insulin test period

Glucose levels during the test

Basal testing worksheet