At a Glance

Type I diabetes is a disease typically diagnosed in children and young adults and accounts for only 5-10% of those with diabetes. Patients with type I diabetes fail to produce insulin, resulting in excess blood glucose levels. Symptoms of type 1 diabetes include:

  • increased thirst

  • frequent urination

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  • extreme hunger

  • weight loss

  • fatigue

  • ketoacidosis

  • blurred vision

Patients with a parent or sibling with type I diabetes are at increased risk of developing the condition.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

Current diagnostic criteria for diabetes include one of the four following tests: a fasting plasma glucose (FPG) level greater than or equal to 126 milligrams/deciliter (mg/dL) (7 millimoles/liter) (mmol/L), where fasting is defined as no caloric intake for more than 8 hours; elevated 2 hour plasma glucose greater than or equal to 200 mg/dL (11.1 mmol/L) following a glucose load containing 75-grams (g) anhydrous glucose dissolved in water during an oral glucose tolerance test (OGTT) an elevated random plasma glucose greater than or equal to 200 mg/dL (11.1 mmol/L) in a patient exhibiting classic symptoms of hyperglycemia or hyperglycemic crisis; or a glycated hemoglobin (A1C) test of 6.5% or higher using a method certified by the National Glycohemoglobin Standardization Program (NGSP).

If any of these criteria are met, testing should be repeated on a subsequent day to establish the diagnosis, except in cases of unequivocal hyperglycemia (
≥200 mg/dL [11.1 mmol/L], accompanied by symptoms consistent with overt hyperglycemia), whereby the existence of one criteria would fulfill the diagnosis.

Diabetes-related autoantibody testing may be used to distinguish between type I and type II diabetes. The four most common autoantibody tests include Islet cell Cytoplasmic Autoantibodies (ICA), which is used to identify a variety of islet cell proteins detected in approximately 70-80% of newly diagnosed type I diabetes; Glutamic Acid Decarboxylase Autoantibodies (GADA), which test for autoantibodies directed against beta cell protein commonly detected in 70-80% of new diagnoses; Insulinoma-Associated-2 Autoantibodies (IA-2A), which are also a nonspecific test for autoantibodies against beta cell antigens present in approximately 60% of type I diabetes; and Insulin Autoantibodies (IAA), which are present in about 50% of type I diabetic children.

Because the autoantibodies detected in children differ from those detected in adults, IAA is typically ordered for diagnosing children, whereas ICA, GADA, and IA-2A are used for diagnosing adolescent and adult type I diabetes.(Table 1)

Table 1.
FPG ≥126 mg/dL (7 mmol/L)
2 h plasma glucose (OGTT, 75 g) ≥200 mg/dL (11.1 mmol/L)
Random plasma glucose ≥200 mg/dL (11.1 mmol/L), accompanied by classic symptoms of hyperglycemia
A1C ≥6.5%

Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications – OTC drugs or Herbals – that might affect the lab results?

Given inherent variability in all laboratory testing (both preanalytical and analytical), it is possible that patients with a lab result over the threshold for diabetes will have a repeated value near the margins but below the diagnostic criteria for diabetes. It is recommended that such patients be monitored closely and their testing be repeated in approximately 3-6 months.

A drop in glucose levels may occur if the specimen is not taken to the lab immediately, leading to inaccurate reporting of blood glucose levels. It is recommended that blood be drawn in a gray-top tube containing sodium fluoride, which will inhibit glycolysis within 1 hour. Blood samples drawn in a red-top tube for serum glucose or in a green-top tube for plasma glucose will demonstrate a 2-3% decrease in glucose concentration per hour. In addition, patients suffering from sepsis or conditions that result in high white blood cell counts, such as chronic lymphocytic leukemia, may have artificially low glucose concentrations because of an increased rate of glucose metabolism as a consequence of leukocytosis and activated neutrophils.

Mean FPGs tend to be higher earlier in the day, thus, it is recommended that blood for this test be drawn in the morning. In addition, plasma glucose levels typically vary from day to day and can be affected by other factors, such as acute stress.

Although the A1C test can overcome many of the mentioned issues, caution in interpreting results from this test must be used as hemoglobinopathies. Patient age and other medical illnesses that affect red blood cell survival make interpreting the results difficult. Thus, use of this test may result in an over-diagnosis of the elderly, African-Americans, patients with an iron deficiency, or patients genetically predisposed to increased levels of hemoglobin concentration. A correlation between decreased A1C levels and pregnancy has also been well documented. Likewise, use of the A1C test alone may not be adequate in the diagnosis of diabetes in patients with anemia, hemoglobinopathies, or kidney disease.

What Lab Results Are Absolutely Confirmatory?

Laboratory tests used for diagnosis are also used for confirmation. Typically, if a lab test results in the diagnosis of diabetes, the same test is repeated on a subsequent day for confirmation. If results are simultaneously available for two separate tests and both indicate diabetes, additional testing is not required for confirmation. If, however, the results are discordant, the test with results above the diagnostic threshold for diabetes should be repeated. Diagnosis is then based on the results of the repeated test.

Additional Issues of Clinical Importance

Failure to diagnose type I diabetes can result in disabling and/or life-threatening complications, such as heart and blood vessel disease, nerve damage (neuropathy), kidney damage (nephropathy), eye damage, foot damage, skin and mouth conditions, osteoporosis, pregnancy complications, and hearing problems. In addition, type I diabetics are also at increased risk for other autoimmune Graves’ disease, Hashimoto’s thyroiditis, Addison’s disease, vitiligo, celiac sprue, autoimmune hepatitis, myasthenia gravis, and pernicious anemia.

Following a diagnosis of diabetes, patients should seek care from a medical team comprised of physicians, nurse practitioners, physician’s assistants, nurses, dietitians, pharmacists, and mental health professionals to implement a management plan for their disease.

In nonpregnant adults, the American Diabetes Association (ADA) recommends an A1C goal of less than 7.0%, a preprandial capillary plasma glucose of 70-130 mg/dL (3.9-7.2 mmol/L), and a peak post prandial capillary plasma glucose (2 hours after eating) greater than 180 mg/dL (<10 mmol/L). For women with type I or type II diabetes who become pregnant, the optimal glycemic goals set by the ADA include a premeal, bedtime, and overnight glucose of 60-99 mg/dL (3.3-5.4 mmol/L), a peak postprandial glucose of 100-129 mg/dL (5.4-7.1 mmol/L), and an A1C greater than 6.0%. Alternatively, the American Association of Clinical Endocrinologists recommends blood glucose goals of 110 mg/dL (6.2 mmol/L) preprandial, 140 mg/dL (7.8 mmol/L) peak postprandial, and an A1C of 6.5%.

When establishing a treatment plan for achieving glycemic goals, it is important to consider patient age, duration of diabetes, and presence of cardiovascular disease to reduce the risk of hypoglycemic events.

Self-monitoring of blood glucose (SMBG) should be performed by all insulin-treated patients with diabetes. Although SMBG may benefit type II diabetics treated with diet and oral agents, the data are currently insufficient to claim improved health outcomes. A1C testing is recommended biannually in all diabetic patients and quarterly for patients whose therapy has changed or who are not meeting treatment goals.(
Table 2) (Table 3)

Table 2.
Plasma glucose goal mg/dL (mmol/L)
Patient Category (years of age) Preprandial Bedtime Peak Postprandial A1C (%)
0-6 100-180 (5.6-10.0) 110-200 (6.2-11.1) <8.5
6-12 90-180 (5.0-10.0) 100-180 (5.6-10.0) <8.0
13-19 90-130 (5.0-7.2) 90-150 (5.0-8.3) <7.5
>19, nonpregnant 70-130 (3.9-7.2) 100-140 (5.6-7.8) <180 (<10.0) <7.0
>19, pregnant with pre-existing diabetes 60-99 (3.3-5.5) 100-129 (5.6-7.2) <6.0
Table 3.
Parameter ADA Recommendation
Blood pressure <130/80 mmHg
Low density lipoprotein <100 mg/dL (2.6 mmol/L)
Triglycerides <150 mg/dL (<1.7 mmol/L)
High density lipoprotein >40 mg/dL (>1.1 mmol/L)

Errors in Test Selection for Type 1 Diabetes

Point of care testing is currently not accurate enough to be used for the diagnosis of diabetes.

A1C testing is recommended for the diagnosis of diabetes in nonpregnant adults only.

In cases of rapidly evolving diabetes, it is possible to find an A1C not significantly elevated despite overt diabetes. In these cases, the established glucose criteria should be used for diagnosis.