One type of testing that may be done is autoantibody testing. When Type 1 diabetes or latent autoimmune diabetes in adults (LADA) is suspected, a blood test that screens for autoantibodies to islet cells, insulin, and glutamic acid decarboxylase (and possibly some others) may be done. The presence of such autoantibodies indicates that the body is engaged in a destructive immune response against its insulin-producing cells.
Another test that may be done if a doctor suspects Type 1 diabetes or LADA is a C-peptide test. C-peptide is a by-product of insulin formation in the pancreas. The pancreas first creates proinsulin, a large protein that breaks down into three chains of amino acids, two of which recombine to become insulin, and one of which, known as C-peptide, is secreted into the bloodstream along with insulin. While the function of C-peptide is currently not known, a person’s C-peptide level gives an indication of how much insulin his pancreas is producing.
Infants who develop diabetes within the first six months of life may undergo genetic testing to see whether they have a rare form of diabetes called neonatal diabetes, which occurs because of a genetic defect. Neonatal diabetes may be mistaken for Type 1 diabetes, but infants who have it may do better when treated with sulfonylureas (a type of oral drug) than with insulin.
Another type of diabetes that is caused by a genetic defect is Maturity Onset Diabetes of Youth (MODY). In fact, there are several varieties of MODY, each caused by a different gene abnormality. Some forms of MODY can be treated well with pills, while others require insulin therapy. Because genetic testing for MODY is expensive, it is not done frequently. However, if a parent has a form of MODY, his children have a 50% chance of also having it. Detecting it early in children allows for early treatment and possibly prevention of long-term complications.
When to screen
Currently, the ADA recommends testing for diabetes when a person has symptoms of diabetes such as frequently passing large volumes of urine, excessive thirst, weight loss, and sometimes increased hunger and blurred vision.
The ADA states that health-care providers should consider screening for Type 2 diabetes in adults of any age who are overweight or obese and who have one or more additional risk factors for Type 2 diabetes. Those risk factors include the following:
- Physical inactivity
- Having a first-degree relative with diabetes
- Being a member of an ethnic population with a high prevalence of diabetes (African-American, Latino, Native American, Asian American, Pacific Islander)
- Having delivered a baby weighing more than 9 pounds or having been diagnosed with gestational diabetes
- Having high blood pressure (equal to or higher than 140/90 mm Hg) or being treated for high blood pressure
- Having an HDL cholesterol level lower than 35 mg/dl and/or a triglyceride level higher than 250 mg/dl
- Having polycystic ovary syndrome
- Having an A1C equal to or greater than 5.7% or having been diagnosed with impaired glucose tolerance or impaired fasting glucose on a previous occasion
- Having other conditions associated with insulin resistance such as severe obesity or acanthosis nigricans (a darkening of the skin that commonly occurs in the folds of the armpits, neck, or groin)
- Having a history of cardiovascular disease
In adults without these risk factors, the ADA states that diabetes screening should begin at age 45. If tests do not show elevated blood glucose, testing should be repeated at least every three years.