Focus on Type 2 Diabetes

Because the majority of diabetic patients have type 2 diabetes, the rest of this web module will focus on diagnosis and management of this population.

The Development of Type 2 Diabetes

In type 2 diabetes, it is important to remember that insulin resistance and beta cell dysfunction are closely linked.

ADA Short Film: “What Happens in Type 2 Diabetes” (1 min 11 secs.)

Before type 2 diabetes fully develops (“pre-diabetes” period), insulin resistance may already be present. During this time, insulin secretion is usually increased, but fasting and post-parandial glucose blood levels may still be normal.

At some point, type 2 diabetics can no longer increase or maintain insulin secretion levels to compensate for increasing insulin resistance. Initially, mild to moderate glucose intolerance will develop. Over several years, insulin secretion can no longer meet insulin needs and eventually fasting hyperglycemia develops. Once fasting glucose exceeds 126 mg/dL, diabetes is present (point C on the graph).

Development of Type 2 Diabetes

Development of Type 2 Diabetes Graph

The natural history of the disease suggests prevention and early treatment is paramount. It also suggests that combination therapy for type 2 diabetes will likely play a role in most patients in order to address the insulin resistance and deficiency.

Diagnosis of Pre-diabetes and Type 2 Diabetes

Question 1:

 A patient can also be diagnosed with diabetes mellitus based on an elevated Hemoglobin A1C.
(Choose the one best answer)

  1. True
  2. False
Show answer >>

The correct answer is B - FALSE. The use of HgA1C for the diagnosis of diabetes is NOT recommended at this time.

The diagnosis of impaired glucose tolerance or pre-diabetes is included in the table below.

Normoglycemia

Impaired Glucose Tolerance
(Pre-diabetes)

Diabetes*
FPG <100 mg/dL
FPG 100-125 mg/dL (Impaired Fasting Glucose = IFG)
FPG ≥126 mg/dL
2 hr OGTT < 140 mg/dL
2 hr OGTT 140-199 mg/dL (Impaired Glucose Tolerance = IGT)
2 hr OGTT ≥ 200 mg/dL
   
Symptoms of diabetes and casual plasma glucose concentration ≥ 200 mg/dL
  • Diagnosis of diabetes must be confirmed on a subsequent day unless unequivocal symptoms of diabetes are present.
  • FPG = Fasting Plasma Glucose
  • OGTT = Oral Glucose Tolerance Test
 

 

Diagnosing Diabetes

The fasting plasma glucose (FPG) is the preferred test to diagnose diabetes in children and non-pregnant adults. It is easier to administer, convenient, acceptable to patients, and costs less. Fasting is defined as no caloric intake for at least 8 hours. An FPG equal or greater than 126 mg/dL will diagnose a patient with diabetes. A diagnosis of diabetes must be confirmed on a subsequent day unless unequivocal symptoms of diabetes are present.
The 75-gram oral glucose tolerance test (OGTT) is more sensitive and slightly more specific than the FPG. It is poorly reproducible, more expensive, and inconvenient for patients, and rarely used in clinical practice. A plasma glucose equal to or greater than 200 mg/dL drawn 2 hours after an OGTT is diabetes. Once again, a diagnosis of diabetes must be confirmed on a subsequent day unless unequivocal symptoms of diabetes are present.
A casual (any time of day regardless of last meal) plasma glucose greater than 200mg/dL and classic symptoms of diabetes (polyuria, polydypsia, unexplained weight loss) makes the diagnosis and does not need to be repeated on a subsequent day.

Diagnosing Pre-diabetes: IFG and IGT

The diagnosis of pre-diabetes can be categorized as “impaired fasting glucose” (IFG) or “impaired glucose tolerance” (IGT). IFG is defined by an elevated fasting plasma glucose (FPG) concentration (≥100 and <126 mg/dL). IGT is defined by an elevated 2-hour plasma glucose concentration (≥140 and <200 mg/dL) after a 75-g glucose load on the oral glucose tolerance test (OGTT) in the presence of an FPG concentration <126 mg/dL. Screening for IFG/IGT pre-diabetes is identical to screening for diabetes. Because IFG/IGT and diabetes have the same risk factors, screening for IFG/IGT and diabetes should occur in the same patient population. Currently, FPG and 2-hour OGTT are the recommended tests for detecting all states of hyperglycemia. According to the Panel, the most efficient testing sequence is an FPG (the preferred test to detect diabetes) followed by the 2-hour OGTT on a subsequent day to identify combined IFG/IGT.

Screening for Diabetes

One third of adults with diabetes in the United States remain undiagnosed. 50% of undiagnosed patients are eventually diagnosed after complications of diabetes develop especially cardiovascular complications. Screening for diabetes allows for both diagnosis and intervention at earlier stages and may even prevent diabetes from developing.  The fasting plasma glucose test (FPG) is the preferred test to diagnose diabetes in children and non-pregnant adults.

Criteria for testing for diabetes in asymptomatic adult individuals as per the American Diabetes Association

1. Testing for diabetes should be considered in all individuals at age 45 years and above, particularly in those with a BMI 25* and, if normal, should be repeated at 3-year intervals.

2. Testing should be considered at a younger age or be carried out more frequently in individuals who are overweight (BMI 25*) and have additional risk factors, as follows:

*May not be correct for all ethnic groups. PCOS, polycystic ovary syndrome.

Testing for type 2 diabetes in children as per the American Diabetes Association

The incidence of type 2 diabetes in children and adolescents has dramatically increased in the past 10 years. Only children at increased risk for the presence of the development of type 2 diabetes should be tested.

Criteria:

Plus any two of the following risk factors:

Age of initiation: age 10 years or at onset of puberty, if puberty occurs at a younger age

Frequency: every 2 years

Test: FPG preferred

Clinical judgment should be used to test for for diabetes in high-risk patients who do not meet these criteria. PCOS, polycystic ovary syndrome.

Testing for type 2 diabetes in postpartum women with gestational diabetes as per the American Diabetes Association

Question 2:

When should women with gestational diabetes (GDM) and no pre-pregnancy history of diabetes be screened initially for diabetes mellitus? (Choose the one best answer.)

  1. 24 to 48 hours postpartum
  2. 2 weeks to 4 weeks postpartum
  3. 6 weeks to 12 weeks postpartum
  4. 6 months
  5. They do not need to be screened.
Show answer >>
The correct answer is C. Women with GDM should be screened for diabetes 6 – 12 weeks postpartum and should be followed up with a subsequent screening for the development of diabetes or pre-diabetes.

Move on to Next Section...