Islet cell antibody, IgG antibodies (ICA, method IFT)
Why this test?
For early diagnosis of autoimmune diabetes (type 1 diabetes),
For the differential diagnosis of adult autoimmune diabetes (LADA) and type 2 diabetes,
For the diagnosis of pre-diabetes,
To identify the predisposition and assess the risk of developing type 1 diabetes,
To predict the need for insulin therapy in patients with diabetes.
In what cases is it prescribed?
When examining children and adults with a high risk of developing diabetes (whose close relatives have type 1 diabetes),
When examining people with hyperglycemia or impaired glucose tolerance.
Type 1 diabetes mellitus (DM-1, insulin-dependent) is a chronic endocrine disease caused by the autoimmune destruction of beta cells of the islet tissue of the pancreas, which leads to an absolute deficiency of insulin and an increase in blood sugar. Violations of carbohydrate metabolism and clinical manifestations of diabetes occur when more than 80% of beta cells are destroyed. The disease usually appears in childhood and adolescence.
Type 1 diabetes is characterized by the presence of autoantibodies, which have direct pathogenetic significance in the destruction of insulin-producing cells and the development of the disease. A similar mechanism of development and spectrum of antibodies is found in autoimmune diabetes of adults (LADA), which has recently been considered a variant of type 1 diabetes, which occurred later, but is often diagnosed as type 2 diabetes due to age-related features .
Manifestations of diabetes for several years are preceded by an increase in the level of autoantibodies in the blood, which is an early sign of the autoimmune activity of the disease. These antibodies include autoantibodies to glutamate decarboxylase (GAD), protein tyrosine phosphatase (IA2), insulin, and cytoplasmic components of islet cells.
Glutamate decarboxylase (GDK, GAD) is a protein with a molecular weight of 65 kDa, which is involved in the synthesis of the inhibitory neurotransmitter of the central nervous system - gamma-aminobutyric acid (GABA). GAD is expressed in the central and peripheral nervous systems, in the islets of the pancreas, testicles, ovaries, thymus gland and stomach. The sera of 70-80% of people with pre-diabetes and newly diagnosed type 1 diabetes react with this antigen.
Tyrosine phosphatase (IA-2) is an autoantigen of islet cells localized in dense granules of pancreatic beta cells. Antibodies to it are found in 50-75% of patients with type 1 diabetes, even before the first clinical manifestations. According to some reports, IA-2 together with insulin antibodies are more common in children than in adult patients and indicate aggressive destruction of beta cells.
With the course of the disease, the level of autoantibodies in the blood gradually decreases, which is associated with the destruction of the antigenic substrate. In this regard, in patients who have been suffering from type 1 diabetes for a long time, the determination of autoantibodies may have a low diagnostic value.
The level of antibodies to GAD, IA-2, insulin (IAA) and islet cell cytoplasmic component antigens (ISA) is of great importance for the diagnosis and prognosis of type 1 diabetes in close relatives of diabetic patients. The very fact of detection of antibodies can be considered as a predictor of TDM-1, rather than the determination of some particular type of them. Some studies have shown that it is the presence of autoantibodies to GAD and IA-2, rather than phenotypic characteristics, that determine to a greater extent the likelihood of needing insulin therapy. The presence of several autoantibodies significantly increases the risk of developing the disease in the future compared to an isolated increase in one type of antibody.
Test systems have been developed both for the complex determination of autoantibodies and for the detection of their individual types. The sensitivity of the joint measurement of anti-GAD / IA-2 levels for the diagnosis of type 1 diabetes is 96%, the specificity is 98%. Antibodies are detected on average in 73% of patients with newly diagnosed T1DM, in 95% of people with diabetes for less than 5 years, and in 84% of people with diabetes for more than 5 years.
Detection of the predisposition to the development of diabetes and early diagnosis of the disease allow to apply preventive measures in a timely manner, prescribe adequate treatment and prevent the progression of the disease and the development of complications.