ADA screening recommendations: when to screen to repeat screens based on
findings
Recommendations
Screening for type 2 diabetes with an informal
... [Show More] assessment of risk factors or validated
tools should be considered in asymptomatic adults. B
Testing for type 2 diabetes in asymptomatic people should be considered in adults of
any age who are over- weight or obese (BMI >25 kg/m2 or $23 kg/m2 in Asian
Americans) and who have one or more additional risk factors for diabetes. B
For all people, testing should be- gin at age 45 years. B
If tests are normal, repeat testing carried out at a minimum of 3-year intervals is
reasonable. C
To test for type 2 diabetes, fasting plasma glucose, 2-h plasma glucose after 75-g oral
glucose tolerance test, and A1C are equally appropriate. B
In patients with diabetes, identify and treat other cardiovascular disease risk factors.
Updated recommendations emphasize that testing for prediabetes and type 2 diabetes
should be considered in children and adolescents younger than 18 years of age who are
overweight or obese (BMI >85th percentile for age and sex, weight for height >85th
percentile, or weight >120% of ideal for height), and have one or more additional risk
factors for diabetes such as (1) maternal history of diabetes or gestational diabetes
during the child’s gestation; (2) family history of type 2 diabetes in first- or seconddegree
relative; (3) race/ethnicity (Native American, African American, Latino, Asian
American, Pacific Islander; and/or (4) signs of insulin resistance or conditions
associated with insulin resistance (acanthosis nigricans, hypertension, dyslipidemia,
polycystic ovary syndrome, or small-
DIAGNOSTIC TESTS FOR DIABETES
Diabetes may be diagnosed based on plasma glucose criteria, either the fasting plasma
glucose (FPG) or the 2-h plasma glucose (2-h PG) value after a 75-g oral glucose
tolerance test (OGTT) or A1C criteria (1,6) (Table 2.2).
FPG, 2-h PG after 75-g OGTT, and A1C are equally appropriate for diagnostic testing. It
should be noted that the tests do not necessarily detect diabetes in the same individuals.
The efficacy of
interventions for primary prevention of type 2 diabetes (7,8) has primarily been
demonstrated among individuals with impaired glucose tolerance (IGT), not for
individuals with isolated impaired fasting glucose (IFG) or for those with prediabetes
defined by A1C criteria.
The same tests may be used to screen for and diagnose diabetes and to detect
individuals with prediabetes. Diabetes may be identified anywhere along the spectrum
of clinical scenarios: in seemingly low-risk individuals who happen to have glucose
testing, in individuals tested based on diabetes risk assessment, and in symptomatic
patients.
Fasting and 2-Hour Plasma Glucose
The FPG and 2-h PG may be used to diagnose diabetes (Table 2.2). The concordance
between the FPG and 2-h PG tests is imperfect, as is the concordance be- tween A1C
and either glucose-based test. Numerous studies have confirmed that, compared with
FPG and A1C cut points, the 2-h PG value diagnoses more people with diabetes.
A1C
The A1C test should be performed using a method that is certified by the NGSP
(www.ngsp.org) and standardized or traceable to the Diabetes Control and
Complications Trial (DCCT) reference as- say. Although point-of-care A1C assays may
be NGSP certified, proficiency testing is not mandated for performing the test, so use of
point-of-care assays for diagnostic purposes is not recommended but may be
considered in the future if proficiency testing is performed and documented.
The A1C has several advantages com- pared with the FPG and OGTT, including greater
convenience (fasting not required), greater preanalytical stability, and less day-to-day
perturbations during stress and illness. However, these
advantages may be offset by the lower sensitivity of A1C at the designated cut point,
greater cost, limited availability of A1C testing in certain regions of the developing
world, and the imperfect correlation between A1C and average glucose in certain
individuals. National Health and Nutrition Examination Survey (NHANES) data
indicate that an A1C cut point of $6.5% (48 mmol/mol) identifies one-third fewer cases
of undiagnosed diabetes than a fasting glucose cut point of $126 mg/dL (7.0 mmol/L)
(9).
When using A1C to diagnose diabetes, it is important to recognize that A1C is an
indirect measure of average blood glucose levels and to take other factors into
consideration that may impact hemoglobin glycation independently of glycemia
including age, race/ethnicity, and anemia/ hemoglobinopathies.
Confirming the Diagnosis
Unless there is a clear clinical diagnosis (e.g., patient in a hyperglycemic crisis or with
classic symptoms of hyperglycemia and a random plasma glucose $200 mg/dL [11.1
mmol/L]), a second test is required for confirmation. It is recommended that the same
test be repeated without delay using a new blood sample for confirmation because there
will be a greater likelihood of concurrence. For ex- ample, if the A1C is 7.0% (53
mmol/mol) and a repeat result is 6.8% (51 mmol/mol), the diagnosis of diabetes is
confirmed. If two different tests (such as A1C and FPG) are both above the diagnostic
threshold, this also confirms the diagnosis. On the other hand, if a patient has
discordant results from two different tests, then the test result that is above the
diagnostic cut point should be repeated. The diagnosis is made on the basis of the
confirmed test. For example, if a patient meets the diabetes criterion of the A1C (two
results $6.5% [48 mmol/mol]) but not
FPG (,126 mg/dL [7.0 mmol/L]), that person should nevertheless be considered to have
diabetes.
Since all the tests have preanalytic and analytic variability, it is possible that an
abnormal result (i.e., above the diagnostic threshold), when repeated, will produce a
value below the diagnostic cut point. This scenario is likely for FPG and 2-h PG if the
glucose samples remain at room temperature and are not centrifuged promptly.
Because of the potential for preanalytic variability, it is critical that samples for plasma
glucose be spun and separated immediately after they are drawn. If patients have test
results near the margins of the diagnostic threshold, the health care professional should
follow the patient closely and repeat the test in 3–6 months.
Description
In 1997 and 2003, the Expert Committee on the Diagnosis and Classification of Diabetes
Mellitus (17,18) recognized a group of individuals whose glucose levels did not meet
the criteria for diabetes but were too high to be considered nor- mal. “Prediabetes” is
the term used for individuals with IFG and/or IGT and/or A1C 5.7–6.4% (39–47
mmol/mol). Pre- diabetes should not be viewed as a clinical entity in its own right but
rather as an increased risk for diabetes (Table 2.3) and cardiovascular disease (CVD).
Prediabetes is associated with obesity (especially abdominal or visceral obesity),
dyslipidemia with high triglycerides and/or low HDL cholesterol, and hypertension.
Diagnosis
The Expert Committee on the Diagnosis and Classification of Diabetes Mellitus (17,18)
defined IFG as FPG levels be- tween 100 and 125 mg/dL (between 5.6 and 6.9 mmol/L)
and [Show Less]