Basal Testing

Basal testing is one of those things that you are not going to learn from a doctor.  I first learned how to do it because of reading message boards.  It seems like some people think it is only for pumpers, but it is beneficial for people on MDI to do also.  I did it when I was on Levemir and by doing basal testing, I knew that I had my levels set correctly.  More importantly, I knew that Levemir was starting to wear off at 7 hours for me, so taking it twice a day would not work.  I never did basal testing when I was using Lantus, and even though I am very glad that I switched to Levemir, I do have to wonder if I could have gotten Lantus to work better by having better basal rates. 

I believe that having your basal rates set correctly is a very important piece of being able to be in good control.  It is like having a good foundation for your house.  You can build a nice big, well constructed house, but if you put it on a faulty foundation, it will come tumbling down.  If your basal rates are not set correctly, your carb ratios or correction rates won’t work either. 

In the book Using Insulin, John Walsh recommends doing the basal test in 8 hour shifts, with the overnight period being the most important.  Not too many people do what I do, but when I do mine, I do it for a full 24 hours.  I figure if I am testing to check and see how long insulin lasts, doing it for 8 hours will not work.  Even though I am now on a pump and I know I have basal insulin pumping into my system that is not going to run out, I still try to do my basal test for the full 24 hours.  Since I have gastroparesis, I know for sure that I don’t have food lingering in my stomach.

The idea behind basal testing is to have your basal insulin stay fairly stable.  I had always read that your blood sugar should not go up or down by more than 30 points from your starting blood sugar.  If you started at 100, you should not drop lower than 70 or go higher than 130.  When I read Using Insulin, John Walsh actually recommends that it drop no more than 30 points, but should not rise more than 15 points.  That is a little bit of a tighter spread than what I had originally learned.  Gary Scheiner recommends 30 points both directions. 

When you start the test, you want to make sure that any fast acting insulin is out of your system.  You always want to wait a few hours after your last meal to make sure any food you ate is digested.  You should not drink any caffeinated beverages because caffeine can raise your blood sugar.  Although you should continue to do regular activities, you also don’t want to do very strenuous things that you know will cause your blood sugar to drop. 

You should test your blood sugar every 1-2 hours.  I prefer to check every hour because if I go two hours and my blood sugar changed by more than 30 points, I would like to know if it changed closer to that 1 hour or 2 hours.  But that is just my personal preference!  If your starting blood sugar is too high or two low, then you would want to do the test at a different time.  If you start at a good range and need to treat for a high or low, then you will have to stop the test.

If your blood sugar starts dropping low, you know that you are taking too much basal insulin and should adjust your basal rates accordingly.  If you start to go high and need a correction bolus, then you should also increase the amount of basal testing.

The past week, I have been having some whacky blood sugars so I wanted to see if I needed to adjust my basal rates.   Yesterday morning, was my second attempt at “wanting” to do basal testing, but my blood sugar crashed both yesterday and Tuesday mornings. When my blood sugar crashed yesterday, I dropped to 39.  I obviously over treated because one hour later, I was 290.  That is not exactly what I had in mind for doing a basal test!

By about 10:30, my blood sugar was hanging out in the 90s.  I had a dentist appointment around noon, so checked my blood sugar after I was done with that.  My correction bolus for the 290 was at 8:29.  I use Apidra and that gets out of my system fairly fast so I knew I would be good to go.  At 12:56 PM, I was 108 so I used 108 as my starting number.  If I use the 30 point spread, I should not drop lower than 78 or go higher than 138.  If I wanted to use the 15 points for the high number, then I should not go over 123. 

I always like to drop my results onto a spreadsheet have a formula to let me know the difference from my beginning number – I wasn’t dubbed the spreadsheet queen for nothing!  The areas shaded in blue are where I have the formulas.


On the line that says “high,” I have a formula that if the difference in the numbers is greater than 30, the formula will show High as the result.  If the number is not greater than 30, then the result will put a period (so the space looks blank).  On the line that says “low,” the formula is if the number is less than negative 30 and the result will show Low.  I also added the High 15 line to show if my blood sugar went up by more than 15 points. 

As you can see, I went above the 15 point spread about 8 PM and above the 30 point spread at 10 PM.  Because I have a basal rate change at 7 PM, I need to bump by basal rate up a little.  You really should change your rates a couple hours before they need to kick in.  Changing it at 7 PM won’t do anything for it being over the 15 point spread at 8 PM, but I would like to see what my change does before I decide whether or not I will move the time back an hour.  I have only been pumping for six months, but so far, having it change at 7 PM has worked.  

You should always wait 2-3 days in between making changes to give things a chance to level out before changing things again.  I will wait a couple days and then try the test again.  Since I now know that my afternoon levels work really good, for the next basal test, I will have an easy to digest lunch (Boost Glucose Control) and start the test late afternoon. 

I am hoping to get a nice flatline picture that looks similar to this on my Dexcom except for 24 hours and not 6 hours.

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