Finger Sticks — Your Real-Time Blood Sugars

By Wil Dubois

A super-quick review for those of you who snuck into this article from the back door: we dFolk are bombarded with numbers, goals, and targets. We're frequently told where we should be, but not how high our risk is when we can't reach our targets. In this series of discussions we look at all of our important numbers and break them down into a simple green light, yellow light, red light format to put all of your critical numbers into a useful context. To give you perspective on when and how much to worry. When to relax, when to call your doc, and when to call 911.

Green light finger stick reading

If you're fasting, which is to say you haven't eaten for quite a while, your blood sugar ought to be somewhere between 76 and 139 mg/dL (4.22 and 7.22 mmol/l). Many doctors are a lot happier if you're between 95 and 115 (5.28 and 6.39 mmol/l). If you're not fasting, of course your numbers are going to be higher. Non-fasting numbers are called "random" readings. Your random green light is below 180 (10 mmol/l).

Yellow light finger stick reading

When it comes to blood sugar, put on the brakes when you see a yellow light. You're on your way to trouble. Yellow lights on the higher end of the blood sugar range are those that are between 131 and 248 mg/dL (7.28 and 13.83 mmol/l) if you are fasting, and between 181 and 249 mg/dL (10.06 and 13.83 mmol/l) for randoms. On the low end, a yellow light is between 76 and 50 mg/dL. (Taking on some sugar will raise your blood glucose back into the green.) But remember that traffic laws are different in every city. Context, type of diabetes, and type of therapy all play a role here. I personally start getting nervous any time I'm below 85 mg/dL (4.72 mmol/l). But I'm a type 1 on an insulin pump, so my therapy is fast-acting insulin only. I'm at greater risk of a dangerous low than a type 2 on oral medications. Also, for me, an 85 first thing in the morning doesn't upset me as much as an 85 a couple hours after eating.

Red light finger stick reading

It really doesn't matter what time of day it is, or if you're fasting or if you just ate — if your blood sugar is over 250 (13.89 mmol/l), you just ran a red light. Why? Because at 250, your blood is changing. It's becoming sluggish, the cells rigid. The sugar in your blood is making it corrosive, like a mild battery acid. It won't kill you. Not right away. But staying at this level for any period of time is...dangerous. On the other end of the scale, any blood sugar below 49 (2.72 mmol/l) is also a big-time red light. Once you are below 49, the risk of a "blackout" becomes very real.


The fasting finger stick green light is between 76 and 130 mg/dL (4.22 mmol/l and 7.22 mmol/l).
The random finger stick green light is below 180 mg/dL (10 mmol/l)

The high finger stick yellow light is between 131 and 249 mg/dL (7.28 and 13.83 mmol/l)
The low blood sugar finger stick yellow light is between 76 and 50 mg/dL (4.22 and 2.78 mmol/l)

The high blood sugar finger stick red light is more than 250 mg/dL (13.89 mmol/l).
The low finger stick red light is below 46 mg/dL (2.72 mmol/l).


Read Diabetes by the Numbers in full

Last Modified Date: November 28, 2012

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