Driving and Hypoglycemia

Driving and Hypoglycemia

Author: Judy Kohn, RN, BSN, CDE

Last Updated: Friday, March 31, 2006

Q: "How low can your blood sugar go before you go unconscious? I have had several episodes where I passed out due to low blood sugar. I even once wrecked my truck because I blacked out and ran off the road after driving 4 miles. Luckily I was the only car involved. When the paramedics came, they checked my blood sugar and it was 23. How low can it go before you can’t come out of it?:

A: Naturally I am very concerned because the situation you described is serious and one that needs immediate attention so that you can prevent future occurrences. I can't tell from your message if this was a recent occurrence or not, and you did not describe your insulin regimen. While I have already responded to you individually urging you to contact your doctor immediately, I wanted to post this message for the benefit of others in your situation.

Level of Glucose to Cause Loss of Consciousness:

• Although I have extensive references on hypoglycemia, it is very difficult to find a definite answer to your question for a variety of reasons:
• Until only recently, many glucose meters did not read below 40 mg/dl, and even if they did, their accuracy was not as reliable at low levels.
• When you are in severe hypoglycemia, your body attempts to correct/reverse the problem by releasing counter-regulatory hormones that stimulate the liver to release glucose. Thus, sometimes the glucose is already rising at the time the blood glucose is tested by the paramedics.
• Most references explain that you begin to develop impaired thinking when the glucose gets below 50, but it depends somewhat on how rapid your glucose falls, as well as whether you have hypoglycemia unawareness. In the link I provide below on hypoglycemia unawareness, I explain the role of the hormones that attempt to protect you.
• A JDF Countdown article (no date available) provided these approximate numbers: Coma can occur at glucose levels around 30, convulsions at 20, and permanent brain damage at 10. However it is very important to note that these numbers are simply not true or exact for everyone. Research has shown that you can develop memory loss and other impairments from repeated low blood glucose, even if it doesn’t get all the way down to 10.
• It is important to note that other factors can interfere with your ability to recover from hypoglycemia—most importantly: how much insulin is in your system, recent alcohol ingestion (which prevents the liver from being able to release glucose and can cause low glucose up to 12 hours later), how much food is in your system, and how long since you exercised, among other factors. For example, exercise can affect your blood glucose from 12-72 hours later, causing a delayed hypoglycemia

Hypoglycemia Unawareness:

Another concern is whether or not you have hypoglycemia unawareness, a condition in which you have lost your ability to recognize symptoms of low glucose. This is obviously a serious problem, but interestingly, sometimes it is reversible with careful management of your diabetes.

Driving Dangers:

Studies have shown that many people with diabetes cannot accurately judge their blood glucose or their ability to safely drive when their glucose is low. Even if they perceived they were low, they often thought they could drive safely. Yet, while a study showed that driving was impaired at blood glucose levels below 70 mg/dL, the subjects didn’t treat their hypoglycemia until they were below 50 mg/dL.

What might have been occurring in your situation is that you could have had several severe lows, but not low enough to require medical attention. These repeated lows could contribute to your developing hypoglycemia unawareness. In addition, if you were stopped by the highway patrol or treated by the paramedics but were not taken to the hospital, it is possible that no one notified your doctor. State laws vary, but in some states, if you are treated at a healthcare facility for being unconscious, the doctor is required to notify the DMV, and sometimes you may temporarily lose your driving privileges.

Contact Your Doctor Immediately:

Regardless, what concerns me most is that it seems that you might not be communicating this situation to your doctor.

Please note that in almost all cases, the situation you described should be preventable with proper education as well as using the appropriate insulin regimen, and testing frequently. For people with severe extremes in blood glucose, generally the best options are either a multiple shot regimen using a rapid-acting insulin with each meal, and a long-acting at bed, or an insulin pump.

So as I have repeatedly said in this message, it is very important that you get help as soon as possible for this situation, and take action to prevent having any further lows.

Related Questions

Insulin Pumps
Q: "I was wondering what the pros / cons were of using a pump. I currently take 5-6 shots per day, and my doctor suggested I switch to the pump, but I'm having some misgivings about being "plugged in" all..."

Hypoglycemia Unawareness
Q: "I never feel myself going low until I'm there so I need to remember to take a snack before I exercise. Why don't I get a warning? I used to but don't anymore and I'm insulin resistant too."

Hypoglycemic Reaction
Q: "I've been diagnosed as type 2 since March of this year with a BG of 547 (I had infections). I take one 10 mg Glucotrol in the morning and one 500 mg Metformin in the morning and one in the afternoon. ..."

Brittle Diabetes
Q: "Can you please explain the concept of "brittle" diabetes vs. the theory it is just not controlled? Also, does the length of the disease make a difference in one's ability to control it?"

Using Lantus® (Glargine)
Q: "I am currently taking Ultralente® 2x daily (breakfast 10U, dinner 13U). If I switched to a once daily injection of Lantus®, how would my dosage change? What time do you t..."

DOC09389-Rev-A 01/07