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ABC of Diabetes
by Peter J. Watkins
What is diabetes?
Diabetes once diagnosed is
for life. The perseverance and self discipline needed over a
lifetime can often tax even the most robust of people to the
limit. Those caring for them also require perseverance and
an understanding of humanity combined with a cautious
optimism, to guide those with diabetes through the peaks and
troughs of their lives.
Definition
Diabetes occurs either because of a lack of insulin or
because of the presence of factors that oppose the action of
insulin. The result of insufficient action of insulin is an
increase in blood glucose concentration (hyperglycaemia).
Many other metabolic abnormalities occur, notably an
increase in ketone bodies in the blood when there is a
severe lack of insulin.
Diagnosis
The diagnosis of diabetes must always be established by a
blood
glucose measurement made in an accredited laboratory.
Glucose tolerance test
The glucose tolerance test is not normally needed in routine
clinical practice, and then only if uncertainty exists in
younger patients, or to establish an exact diagnosis in
pregnancy. For reliable results, glucose tolerance tests
should be performed in the morning after an overnight fast,
with the patient sitting quietly and not smoking; it is also
important that the patient should have normal meals for the
previous three days and should not have been dieting. False
results may also occur if the patient has been ill recently
or has had prolonged bed rest. Blood glucose concentrations
are measured fasting and then one and two hours after a
drink of 75 g of glucose in 250-350 ml water (in children
1·75 g/kg to a maximum of 75 g), preferably flavoured, for
example, with pure lemon juice. Urine tests should be
performed before the glucose drink and at one and two hours.
Interpretation of blood glucose values according to WHO
criteria is shown in the table.
Gestational diabetes
This term embraces the criteria for both diabetes and
impaired glucose tolerance when discovered during pregnancy
(see page 80).
Glucose tolerance tests may also show:
Renal glycosuria - this occurs when there is
glycosuria but normal blood glucose concentrations; this is
a benign condition, only rarely indicating unusual forms of
renal disease. It is worth issuing these patients with a
certificate to prevent them from being subjected to repeated
glucose tolerance tests at every medical examination.
Steeple or lag curve - this is described when fasting
and two hour concentrations are normal, but those between
are high, causing glycosuria; this is also a benign
condition, which most commonly occurs after gastrectomy but
may occur in healthy people.
Impaired glucose tolerance
This is defined in the table. Patients are managed at the
discretion of the physician. In general, no treatment is
given to elderly people, but diet, exercise and weight
reduction are advisable in younger subjects. Over 10 years,
approximately half of those with impaired glucose tolerance
will develop diabetes, one-quarter will persist with
impaired glucose tolerance, and one-quarter will revert to
normal. Pregnant women with “impaired glucose tolerance”
must be treated as if they were diabetic; for interpretation
of the test in pregnancy seen page 80.
Types of diabetes
Type 1 diabetes (previously insulin dependent diabetes) is
due to B-cell destruction, usually leading to absolute
insulin deficiency). It can be immune mediated or
idiopathic.
Type 2 diabetes (previously non-insulin dependent diabetes)
ranges from those with predominant insulin resistance
associated with relative insulin deficiency, to those with a
predominantly insulin secretory defect with insulin
resistance.
Type 1 and Type 2 diabetes are the commonest forms of
primary diabetes mellitus. The division is important both
clinically in assessing the need for treatment, and also in
understanding the causes of diabetes which are entirely
different in the two groups.
Note: The rest of the chapter
is omitted.
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