 126 mg/dL (7.0 mm/L) is consistent with the diagnosis.
Two-Hour Oral Glucose Tolerance Test (OGTT)
In this test, the plasma glucose level is measured before and 2 hours after the ingestion of 75 gm of glucose. DM is diagnosed if the plasma glucose (PG) level in the 2-hour sample is more than 200 mg/dL (11.1 mmol/L). It is also a standard test but is inconvenient and more costly than FPG and has major variability issues. Patients need to consume a diet with at least 150 g per day of carbohydrates for 3 to 5 days and not take any medications that can impact glucose tolerance, such as steroids and thiazide diuretics.
Glycated Hemoglobin (Hb) A1C
This test gives an average of blood glucose over the last 2 to 3 months. Patients with a Hb A1C greater than 6.5% (48 mmol/mol) are diagnosed as having DM. Hb A1C is a convenient, rapid, standardized test and shows less variation due to pre-analytical variables. It is not much affected by acute illness or stress.
Hb A1C is costly and has many issues, as discussed below, including lower sensitivity. Hb A1C should be measured using the National Glycohemoglobin Standardization Program (NGSP) certified method standardized to Diabetes Control and Complications Trial (DCCT) assay. It is affected by numerous conditions such as sickle cell disease, pregnancy, hemodialysis, blood loss or transfusion, or erythropoietin therapy. It has not been well validated in non-white populations.
Anemia due to deficiency of iron or vitamin B12 leads to spurious elevation of Hb A1C, limiting its use in countries with a high prevalence of anemia. Also, in children and the elderly, the relation between Hb A1C and FPG is suboptimal.
For all of the above tests, if the person is asymptomatic, testing should be repeated later to make a diagnosis of diabetes mellitus.
In patients with classic symptoms of hyperglycemia (increased thirst, increased hunger, increased urination), random plasma glucose more than 200 mg/dL is also sufficient to diagnose DM.
FPG, 2-hour PG during 75-g GTT, and Hb A1C are equally appropriate for the diagnosis of DM. There is no concordance between the results of these tests.
Diagnosis of Gestational Diabetes Mellitus
Pregnant women not previously known to have diabetes should be tested for GDM at 24 to 28 weeks of gestation. ADA and American College of Obstetrics and Gynecology (ACOG) recommend using either a 1-step or 2-step approach for diagnosing GDM.
75 gm OGTT is performed after an overnight fast. Blood samples are collected at fasting for 1 hour and 2 hours. GDM is diagnosed if fasting glucose meet or exceed 92 mg/dl (5.1 mmol/l), 1-hour serum glucose of 180 mg/dl (10.0 mmol/l) or 2-hour serum glucose of 153 mg/dl (8.5 mmol/l).
- Step one: Perform a 50-gram glucose challenge test irrespective of the last meal. If PG at 1-hour after the load is greater than or equal to 140mg/dl (7.8 mmol/l), proceed to step 2.
- Step 2: 100 g glucose OGTT is performed after overnight fasting. Cut off values are fasting PG 95 or 105 mg/dl (5.5/5.8 mmol/l), 1-hour PG of 180 or 190 mg/dl (10.0/10.6 mmol/l), 2-hour PG of 155 or 165 mg/dl (8.6/9.2 mmol/l) or 3-hour PG of 140 or 145 mg/dl (7.8/8.0 mmol/l). GDM is diagnosed if two or more PG levels equal to or exceed these cutoffs.
Treatment / Management
For both T1DM and T2DM, the cornerstone of therapy is diet and exercise.
A diet low in saturated fat, refined carbohydrates, high fructose corn syrup, and high in fiber and monounsaturated fats needs to be encouraged. Aerobic exercise for a duration of 90 to 150 minutes per week is also beneficial. The major target in T2DM patients, who are obese, is weight loss.
If adequate glycemia cannot be achieved, metformin is the first-line therapy. Following metformin, many other therapies such as oral sulfonylureas, dipeptidyl peptidase-4 (DPP-4) inhibitors. Glucagon-like peptide-1 (GLP-I) receptor agonists, Sodium-glucose co-transporter-2 (SGLT2) inhibitors, pioglitazone, especially if the patient has fatty liver disease, alpha-glucosidase inhibitors, and insulin, are available. Recent studies have shown that th