U.S. Department of Health and Human Services

Principle 1: Identify Undiagnosed Diabetes & Prediabetes

Why Test for Diabetes and Prediabetes

Glucose and cardiovascular disease risk factor control improves outcomes for people with diabetes, and diabetes is an important cardiovascular disease risk factor. Individuals with prediabetes can prevent or delay onset of type 2 diabetes with weight loss, increased activity, and/or metformin therapy. Detection of individuals with diabetes and prediabetes is essential for identification of individuals who can benefit from evidence-based therapies that can mitigate risk for progression to diabetes as well as modify micro- and macrovascular disease risk.1, 2​​

Whom to test for diabetes and prediabetes, and how often

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Because risk for type 2 diabetes increases substantially with age, and early in the disease’s course most people do not have symptoms (polydipsia, polyuria, unexplained weight loss), screening should be considered in asymptomatic persons over 45 years old. Screening should be considered in adults of any age who are overweight or obese and have one or more additional risk factors listed in Table 1.3 Testing may be repeated at intervals of 1​ to 3 years with the frequency determined by the degree of risk as assessed by risk factors and results of previous tests. For example, people with an A1C closer to 6.5 percent could be tested more frequently than those with an A1C in the normal or near-normal range.

About half of women with a history of gestational diabetes (GDM) will develop type 2 diabetes 2 to 3 decades after pregnancy.4 Because of this significant risk, testing should be done 6 to 12 weeks postpartum and every year thereafter if prediabetes is diagnosed, or every 3 years if the postpartum test is normal.3 Testing is particularly important for women prior to subsequent pregnancy because the risk of fetal abnormalities is higher in women with undetected preconception diabetes.

Generally, people with type 1 diabetes present with acute symptoms of diabetes and markedly elevated blood glucose levels, and some cases are diagnosed with life-threatening diabetic ketoacidosis (DKA). About one-third of children diagnosed with type 1 diabetes present with DKA.5 Participation in observational research is associated with lower risk of DKA in individuals at risk for type 1 diabetes.6 Consider informing people with type 1 diabetes that their first-degree relatives are eligible for clinical research projects that include islet antibody testing to determine risk for type 1 diabetes and test approaches for prevention (e.g., Type 1 Diabetes TrialNet). Such testing and follow-up may alert people to the onset of type 1 diabetes and lower risk for DKA.6, 7

Risk Factors for Type 2 Diabetes

  1. Age ≥ 45 years
  2. Overweight or obese — body mass index (BMI) ≥ 25 kg/m 2 (≥ 23 kg/m 2 for Asian Americans) 8 or waist circumference in men > 40 inches (102 cm) or in women > 35 inches (88 cm) 9
  3. Family history of diabetes (i.e., parent or sibling)
  4. Member of high-risk population: African American, Hispanic/Latino, American Indian, Alaska Native, Asian American, Pacific Islander
  5. History of gestational diabetes mellitus (GDM) or giving birth to a baby weighing ≥ 9 lbs
  6. Physical inactivity
  7. Hypertension
  8. High-density lipoprotein cholesterol (HDL-C) level ≤ 35mg/dL (0.90 mmol/L)
  9. Fasting triglyceride (TG) level ≥ 250 mg/dL (2.82 mmol/L)
  10. Acanthosis nigricans, nonalcoholic steatohepatitis, polycystic ovary syndrome, and other conditions associated with insulin resistance)
  11. Atherosclerotic cardiovascular disease
  12. Depression
  13. Treatment with atypical antipsychotics, glucocorticoids
  14. Obstructive sleep apnea and chronic sleep deprivation (< 6 hours/day) are emerging risk factors.

How to test for diabetes and prediabetes

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A1C and fasting glucose testing are less burdensome than the oral glucose challenge. A1C does not require fasting but is more costly than fasting blood glucose and may be unreliable in certain conditions. People in the early stages of diabetes or with prediabetes may be identified by one test but not the other. Therefore, confirmation with the same test that is above the diagnostic threshold for diabetes should be considered.

The threshold for diagnosis of diabetes, defined by the cut points referenced in Table 2, reflects levels at which risk of microvascular disease increases. There is some variation among guidelines on the cut point for diagnosis of prediabetes and the preferred test. All agree, however, that the risk of diabetes is continuous, extending below the lower limit of the range and becoming disproportionately greater at the higher end of the range.

If health care professionals choose A1C testing for diagnostic purposes, it should be performed in a laboratory using a method that is NGSP certified. Point-of-care A1C tests and finger-stick blood glucose testing should not be used for diagnosis. The A1C test may not be accurate in people with anemia, kidney failure, or liver disease and should not be used for diagnosis of GDM or cystic fibrosis–related diabetes. Some A1C tests give false results in people with hemoglobin variants (e.g., sickle cell trait), but most are free from such interference.

How to test for gestational diabetes

There are two approaches for GDM screening, as outlined in Table 2. GDM screening is recommended for all women, usually between 24 and 28 weeks gestation, who are not previously diagnosed with overt diabetes. Use of the one-step screening approach results in increased diagnosis of GDM.

Test Criteria for Prediabetes, Diabetes, and Gestational Diabetes

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Prediabetes

1. A1C 5.7 percent–6.4 percent or

2. Fasting plasma glucose (FPG) 100–125 mg/dL [impaired fasting glucose (IFG)] or

3. Two hours after 75 g oral glucose challenge, plasma glucose 140–199 mg/dL [impaired glucose tolerance (IGT)]

For the three tests, the risk of diabetes is continuous, extending below the lower limit of the range and becoming disproportionately greater at higher end of the range.

Diabetes

1. A1C ≥ 6.5 percent* or

2. FPG ≥ 126 mg/dL or

3. Two-hour plasma glucose ≥ 200 mg/dL after 75 g oral glucose challenge or

4. Random plasma glucose ≥ 200 mg/dL with symptoms (such as polyuria, polydipsia, and unexplained weight loss)

For criteria 1–3: Repeat test to confirm unless symptoms are present. It is preferable to repeat the same test for confirmation. If two different tests are used (e.g., FPG and A1C), and both indicate diabetes, consider the diagnosis confirmed. If the two different tests are discordant, repeat the test above the diagnostic cut point. 3

* This A1C recommendation is for type 2 diabetes. Use of A1C for diagnosis of type 1 diabetes is not recommended. 10

Gestational Diabetes

Two GDM screening approaches are presented below. GDM screening is recommended for all women, usually between 24 and 28 weeks gestation, who are not previously diagnosed with overt diabetes. Use professional judgment to select the most appropriate test for each woman.

A. A two-step approach endorsed by the American College of Obstetricians and Gynecologists and a consensus panel convened by the National Institutes of Health 11

1. Start with a 1-hour plasma glucose test after 50 g oral glucose challenge. Choose a cutoff of either ≥ 135 mg/dL or ≥ 140 mg/dL and ensure that this cutoff remains consistent.

2. For individuals who meet or exceed the screening threshold, administer a 3-hour 100 g oral glucose tolerance test. Diagnose GDM when two or more of the plasma glucose values are exceeded on the 3-hour test. Choose either of two methods: (1) National Diabetes Data Group cutoff values of Fasting ≥ 105 mg/dL, 1-hour ≥ 190 mg/dL, 2-hour ≥ 165 mg/dL, or 3-hour ≥ 145 mg/dL, or (2) Carpenter and Coustan cutoff values of Fasting ≥ 95 mg/dL, 1-hour ≥ 180 mg/dL, 2-hour ≥ 155 mg/dL, or 3-hour ≥ 140 mg/dL.

B. A one-step approach endorsed by the International Association of Diabetes and Pregnancy Study Groups 12

1. Perform a 75 g oral glucose tolerance test. Diagnose GDM when one or more of the following plasma glucose values are exceeded: Fasting ≥ 92 mg/dL, 1-hour ≥ 180 mg/dL, or 2-hour ≥ 153 mg/dL.

References

1. Cefalu WT. Steps toward the meaningful translation of prevention strategies for type 2 diabetes. Diabetes Care. 2012;35(4):663–5.

2. Fradkin JE, Roberts BT, Rodgers GP. What’s preventing us from preventing type 2 diabetes? N Engl J Med. 2012;367(13):1177–9.

3. American Diabetes Association. Standards of medical care in diabetes—2014. Diabetes Care. 2014;37(Suppl 1):S14–80.

4. American College of Obstetricians and Gynecologists. Practice bulletin no. 137: gestational diabetes mellitus. Obstet Gynecol. 2013;122(2 Pt 1):406–16.

5. Dabelea D, Rewers A, Stafford JM, et al. Trends in the prevalence of ketoacidosis at diabetes diagnosis: the SEARCH for diabetes in youth study. Pediatrics. 2014;133(4):e938–45. doi: 10.1542/peds.2013–2795.

6. Barker JM, Goehrig SH, Barriga K, et al. Clinical characteristics of children diagnosed with type 1 diabetes through intensive screening and follow-up. Diabetes Care. 2004;27(6):1399–404.

7. Diabetes Prevention Trial–Type 1 Diabetes Study Group. Effects of insulin in relatives of patients with type 1 diabetes mellitus. N Engl J Med. 2002;346(22):1685–91.

8. Hsu WC, Araneta MRG, Kanaya AM, et al. BMI cut points to identify at-risk Asian Americans for type 2 diabetes screening. Diabetes Care. 2015;38(1):150–8.

9. Klein S, Allison DB, Heymsfield SB, et al. Waist circumference and cardiometabolic risk: a consensus statement from Shaping America’s Health: Association for Weight Management and Obesity Prevention; NAASO, the Obesity Society; the American Society for Nutrition; and the American Diabetes Association. Diabetes Care. 2007;30(6):1647–52.

10. Vehik K, Cuthbertson D, Boulware D, et al. Performance of HbA1c as an early diagnostic indicator of type 1 diabetes in children and youth. Diabetes Care. 2012;35(9):1821–5.

11. Vandorsten JP, Dodson WC, Espeland MA, et al. NIH consensus development conference: diagnosing gestational diabetes mellitus. NIH Consens State Sci Statements. 2013;29(1):1–30.

12. Metzger BE, Gabbe SG, Persson B, et al. International association of diabetes and pregnancy study groups recommendations on the diagnosis and classification of hyperglycemia in pregnancy. Diabetes Care. 2010;33(3):676–82.