Hypoglycemia is divided into three levels of severity, depending on the symptoms and how difficult it is to get the patient to take some treatment (I discuss treatment in more detail later in this chapter):
i Mild hypoglycemia, which is marked by a blood glucose of about 75 mg/dl, is easily treated by the patient (or caretaker if the patient is a child). Glucose levels come back to normal with small amounts of carbohydrate. Mild hypoglycemia is usually well-tolerated, and the person can go on with his day after he's raised the blood glucose to normal. The diagnosis is usually made during routine testing of the blood glucose rather than by symptoms.
i Moderate hypoglycemia, which is marked by a blood glucose of about 65 mg/dl, is treated by the caretaker by giving two to three glucose tablets, waiting 20 minutes, and testing to make sure the glucose is back to normal. If it isn't normal, more glucose is given. It's recognized as the patient begins to feel the adrenergic symptoms, including rapid heartbeat and anxiety. Moderate hypoglycemia leaves the person unable to function; he doesn't recognize the need for glucose and must be helped.
i Severe hypoglycemia, which is marked by a blood glucose of less than 55 mg/dl, requires the help of someone else to restore the patient's blood glucose. Someone with severe hypoglycemia may be unconscious. It can leave the person with a severe headache and unable to function for lack of glucose in the brain. A shot of glucagon is in order in this situation.
Most people with T1DM have severe hypoglycemia no more than once a year and moderate hypoglycemia no more than twice a week. Mild hypoglycemia occurs about 10 percent of the time as people with T1DM try to keep their blood glucose down.
To interpret a reading accurately, you need to know whether the meter you use to measure blood glucose measures capillary whole blood (the entire blood specimen including the liquid and solid parts like the red blood cells) or plasma (the fluid left when the solid parts are removed). A plasma reading is 11 percent higher than a capillary whole blood reading. My patients use meters that read capillary whole blood, and that's what I use for glucose levels. If your meter reads plasma glucose, add 11 percent to my numbers. For example, a capillary whole blood reading of 80 mg/dl is equal to a plasma reading of 88.8 mg/dl. You can find the information necessary to understand your reading on the meter box or in the instruction manual; if it's not there, call the manufacturer. (Chapter 7 has full details on measuring your blood glucose.)
If moderate or severe hypoglycemia occurs while the person is driving a car or using complex machinery, the result can be devastating. Check your blood glucose before driving, especially if you're driving more than an hour, and stop and check your levels again every few hours. Keep glucose tablets handy in the car (see the later section "Trying other helpful tips" for more about these tablets). If your child has T1DM and is of driving age, make sure that he follows these recommendations.
Studying the effects of severe hypoglycemia on the brain
A major concern with severe hypoglycemia is the possibility of long-term damage to the brain, especially the brain of a developing child who suffers seizures related to hypoglycemia. Numerous studies have looked at this question of long-term damage, and their results differ. One difficulty is determining whether the decline in brain function, if there is any, is due to low blood glucose or episodes of high blood glucose. Here's a roundup of some prominent studies:
I A study from the Journal of Diabetes and Its Complications from January 1999 looked at children diagnosed with diabetes before age 10. Eighteen of 55 patients had a history of severe hypoglycemia with seizures. The children were given tests for memory, academic achievement, and fine motor speed/coordination. Their siblings without diabetes were tested for comparison. In most cases, there was no difference in the test performances of the diabetic children and their nondiabetic siblings; their test results were the same and were normal. The exceptions were children with a history of severe hypoglycemia with seizures, who did more poorly on tests of memory skills, short-term memory, and memory of words. The children with severe hypoglycemia without seizures didn't show this abnormality.
I A study from Diabetologia from January 2002 looked at 64 diabetic children between the ages of 7 and 16 years. They were tested four different times in areas similar to the preceding study. The findings showed a decline in intellectual performance in boys who were diagnosed before age 6 but not in those diagnosed later and not in diabetic girls. However, the decreased intellectual performance wasn't correlated with severe hypoglycemia but rather with poor control of the blood glucose and high glucose readings. The study's authors recommended tighter control of the blood glucose, especially for the younger boys.
I A recent, long-term study in The New England Journal of Medicine in May 2007 compared tight diabetic control with the much looser control that was the standard of care when another study, called the Diabetes Control and Complications Trial (DCCT), took place between 1983 and 1993. The recent study continued to follow these patients for the next decade. In the original DCCT trial, the patients were between the ages of 18 and 34 and had diabetes from 1 to 14 years. Forty percent of the patients reported having at least one coma or seizure due to hypoglycemia. There was no decline in memory or learning function in either the tightly controlled or loosely controlled groups. After following the DCCT patients for an average of 18 years, "no evidence of substantial long-term declines in cognitive function was found . . . despite relatively high rates of recurrent severe hypoglycemia." This is very good news.
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