Biology Reference
In-Depth Information
BG level will be generally high after eating and low when he or she
wakes up in the morning (fasting BG). In diabetes, the timing and
amount of insulin or oral medication additionally disturb these
fluctuations. It has also been shown that the average of several readings
made during the day do not give a good measure of the average BG
level, except under very tightly controlled conditions, because of the
significant irregularity of the BG fluctuations. For example,
Figure 5-2 presents the BG fluctuations of a person with T1DM recorded
over 17 days. Notice the extreme excursions from the target range in
both hypoglycemia and hyperglycemia. (The target BG range for a
person with diabetes was established by the DCCT in 1993: the normal
range is 4.5-5.5 mmol/L, except during the two to three hours after a
meal). This observation also confirms the imperfection of external insulin
replacement discussed in the previous section.
There is a substantial difference in the clinical effects caused by
excursions into the hyper- and the hypoglycemic ranges. Deviations of
the BG into the hyperglycemic range are undesirable, but sharp peaks in
the BG profiles are not immediately dangerous. In contrast, sharp nadirs
could be extremely dangerous and potentially life threatening, because
they indicate hazardously low levels of BG that may cause glucose (fuel)
deprivation of the brain and seizures that preclude self-treatment. For
example, such episodes could be particularly dangerous while operating
a vehicle.
The classic marker of average glycemic status is HbA
1c
, introduced 22
years ago by Aaby Svendsen (Svendsen et al. [1982]). While HbA
1c
has
been linked to long-term complications in both T1DM and T2DM, in
1993, it was also confirmed that the mean BG level for the previous four
to six weeks can be determined by a test of glycosylated hemoglobin,
BG (mmol/L)
21
19
17
15
Hyper-
glycemia
13
11
9
Target
Blood
Glucose
Range
7
5
3
Hypo-
glycemia
1
0
24
48
72
96
120
144
168
192
216
240
264
288
312
336
360
384
408
Time (hours)
FIGURE 5-2.
BG fluctuations of a patient with T1DM. Note the excursions both above and below the target
BG range.
