800
U N I T 9
Endocrine System
classes
8
(Table 33-2). Included are the categories of
type 1 diabetes (i.e., diabetes resulting from beta cell
destruction and an absolute insulin deficiency); type 2
diabetes (i.e., diabetes due to insulin resistance and a
relative insulin deficiency); gestational diabetes mellitus
(i.e., glucose intolerance that develops during pregnancy
that is not clearly overt diabetes [either type 1 or type
2]); and other specific types of diabetes, many of which
occur secondary to other conditions (e.g., Cushing syn-
drome, acromegaly, and pancreatitis).
Categories of Risk for Diabetes
The revised classification system also includes a system
for diagnosing diabetes according to stages of glucose
intolerance.
8–11
The system relies on two tests: (1) a fast-
ing plasma glucose (FPG) test, which measures plasma
glucose levels after food has been withheld for at least
8 hours, and (2) an oral glucose tolerance test (OGTT),
which measures the body’s ability to remove glucose
from the blood within 2 hours of consuming 75 g of
glucose in 300 mL of water.
A FGP below 100 mg/dL or an OGTT less than
140 mg/dL is considered normal (Table 33-3). Persons
whose glucose levels, although not meeting the crite-
ria for diabetes, are too high to be considered normal
are classified as having
impaired fasting plasma glu-
cose
(IFG) and/or
impaired glucose tolerance
(IGT).
Impaired fasting glucose is defined by an elevated FPG
of 100 to 125 mg/dL and IGT as plasma glucose levels
of 140 to 199 mg/dL with an OGTT (see Table 33-3).
Persons with IFG and/or IGT are often referred to as
having
prediabetes
, meaning they are at relatively high
risk for the future development of diabetes as well as
cardiovascular disease.
10,11
Thus, calorie restriction and
weight reduction (even 5% to 10%) are important in
overweight people with prediabetes.
Person with a FPG greater than or equal to
126 mg/dL (7.0 mmol/L) or an OGTT 2-hour glucose
level greater than or equal to 200 mg/dL (11.1 mmol/L)
are considered to have provisional diabetes.
10,11
The cri-
teria in Table 33-3 are used to confirm the diagnosis.
Glycosylated hemoglobin (i.e., HbA
1c
[A1C]) is a widely
used marker for chronic hyperglycemia, reflecting aver-
age blood glucose levels over a 2- to 3-month period of
time (to be discussed). The A1C, which plays a critical
role in the management of persons with diabetes, is now
recommended for use in the diagnosis of diabetes, with
a threshold of greater than 6.5%.
10,11
The test can also
be used to identify persons at higher risk for developing
diabetes (see Table 33-3).
Type 1 Diabetes Mellitus
Type 1 diabetes mellitus, which is characterized by
destruction of the pancreatic beta cells and accounts for
5% to 10% of those with diabetes, is subdivided into
type 1A immune-mediated diabetes and type 1B idio-
pathic (non–immune-related) diabetes.
10
In the United
States and Europe, approximately 90% to 95% of peo-
ple with type 1 diabetes mellitus have type 1A immune-
mediated diabetes. The rate of beta cell destruction is
TABLE 33-2
Etiologic Classification of Diabetes Mellitus
Type
Subtypes
Etiology of Glucose Intolerance
I.Type 1*
Beta cell destruction usually leading to
absolute insulin deficiency
A. Immune mediated
Autoimmune destruction of beta cells
B. Idiopathic
Unknown
II.Type 2*
May range from predominantly insulin
resistance with relative insulin deficiency
to a predominantly secretory defect with
insulin resistance
III. Other specific types
A. Genetic defects in beta cell function
(e.g., glucokinase)
Dysregulation insulin secretion due to a
defect in glucokinase generation
B. Genetic defects in insulin action
(e.g., leprechaunism, Rabson-Mendenhall
syndrome)
Pediatric syndromes that have mutations in
insulin receptors
C. Diseases of exocrine pancreas
(e.g., pancreatitis, neoplasms, cystic
fibrosis)
Loss or destruction of insulin-producing
beta cells
D. Endocrine disorders (e.g., acromegaly,
Cushing syndrome)
Diabetogenic effects of excess hormone
levels
IV. Gestational diabetes
mellitus (GDM)
Any degree of glucose intolerance that
develops during pregnancy that is not clearly
diabetes (either type 1 or type 2)
Combination of insulin resistance and
impaired insulin secretion
*Patients with any form of diabetes may require insulin treatment at some stage of the disease. Such use of
insulin does not, in itself, classify the patient.
Adapted fromThe Expert Committee on the Diagnosis and Classification of Diabetes Mellitus. Report of the
Expert Committee on the Diagnosis and Classification of Diabetes Mellitus. Diabetes Care. 2004;27:S5–S10.
Reprinted with permission from the American Diabetes Association. Copyright © 2004 American Diabetes
Association.
