Be active, not passive, with how you screen for type 2 diabetes

Type 2 diabetes mellitus (DM) is a major health problem, affecting approximately 8% of women in the United States. Furthermore, approximately 25% of people who have diabetes have not been given the diagnosis.¹ From 19 years of age upward, type 2 DM is one of the top 10 causes of death in women.²

Early diagnosis and treatment of type 2 DM can prevent vascular disease and might help reduce premature morbidity and death, but active screening for diabetes has not been emphasized routinely in ObGyn training and care, except during pregnancy. Because the prevalence of diabetes is increasing rapidly—doubling over the past 30 years, in fact³—ObGyns play a central role in effective population screening for diabetes.

Active and passive screening for type 2 DM—what’s the distinction?

There are many recommended approaches to screening for type 2 DM:

• The United States Preventive Services Task Force (USPSTF) advocates a passive approach. The USPSTF concluded that there is insufficient evidence to recommend for or against screening for diabetes except for screening pregnant women and those who are hypertensive.⁴ Simulations of cohorts of patients conclude, however, that passive screening alone would fail to diagnose 38% of cases of diabetes among adults in the United States.⁵
• An active approach to screening, on the other hand, will result in fewer than 5% of cases of type 2 DM being missed.

An approach to active screening. Consistent with guidelines of the American Diabetes Association (ADA)¹ and the American College of Obstetricians and Gynecologists,² one active approach to screening for diabetes is to test, every 3 years:

• all people aged 45 years and older
• all adult women who have a body mass index >25 kg/m² and at least one risk factor for diabetes.

The list of risk factors for diabetes is long. It includes:

• a family history of type 2 DM in a first-degree relative
• a history of gestational DM
• a history of having delivered a baby who weighs more than 9 lb
• a history of polycystic ovary syndrome
• a history of hypertension (blood pressure ≥140/90 mm Hg)
• membership in a high-risk ethnic or racial group (African-American, Hispanic, Native American, Asian-American, and Pacific Islander women)
• dyslipidemia, including a serum high-density lipoprotein level <35 mg/dL or a serum triglyceride concentration >250 mg/dL
• a history of vascular disease.

Active screening by measurement of hemoglobin A_1c

There are three approaches to screening for DM:

• measurement of hemoglobin A_1c (HbA_1c), or glycated hemoglobin, an indicator of blood glucose control over preceding weeks or months (cutoff for a diagnosis of type 2 DM, ≥6.5% on two occasions)
• measurement of the fasting glucose level (cutoff for diagnosis, ≥126 mg/dL on two occasions)
• measurement of serum glucose 2 hours after a 75-g oral glucose load (cutoff, ≥200 mg/dL).

The diagnosis also can be made with one HbA_1c measurement ≥6.5% plus one fasting glucose ≥126 mg/dL.

My preferences and practice. I use the HbA_1c test to diagnose type 2 DM in nonpregnant women because it can be performed at any time of day. I prefer not to use the oral glucose test because it is particularly burden-some—requiring the patient to fast before the test, ingest the glucose load, and return 2 hours later to have the blood glucose level measured.

When my patient’s HbA_1c level is abnormal, I order a second confirmatory HbA_1cor prescribe a home glucose meter and test strips and instruct her to begin measuring the fasting glucose level three to seven times a week. If the home testing regimen shows the fasting glucose level to be consistently ≥126 mg/dL over several weeks, the patient has diabetes.

(*A technical note: HbA_1c testing should be performed in a laboratory that uses a certified and standardized method.)

A word about HbA_1c cutoff values. An HbA_1c concentration <5.7% is normal.* An HbA_1c between 6.0% and 6.4% signals a prediabetic state and a high risk of diabetes; women in this category have a 25% to 50% likelihood of developing type 2 DM within 5 years.⁶

An HbA_1c between 5.7% and 5.9% represents a risk of diabetes—but not as high a risk as does a value between 6.0% and 6.4%. Women whose values fall in this mid-range have a 10% to 25% risk of developing type 2 DM within 5 years. ⁶

Concern about reliability. Red blood cell (RBC) turnover and, therefore, the HbA_1c normal range, are influenced by ethnic and racial background; hemoglobinopathies; thalassemia syndromes; uremia; iron deficiency; and hyperbilirubinemia. Some authorities have concluded that the influence of these variables significantly limits the utility of the test.⁷