Insulin Autoantibody

INAB

36178

1 mL serum

0.2 mL

Plastic screw-cap vial

Room temperature

Room temperature: 28 days
Refrigerated: 28 days
Frozen: 90 days

Set up: Sun, Tues, Thurs; Report available: 3-6 days

In diabetic children <14 years of age (identified by urine screening), the frequency of insulin antibodies (IAA) and islet cell antibodies (ICA) are 43-56% and 84%, respectively; the frequency of both is 40%, and the frequency of one or both is 88%.4 In the same study, cohorts using ICA, GAD-65 antibodies and IAA, sensitivities and specificities are 93% and 93% for any positive, respectively, and 39% and >99%, respectively, for all positives. IAA are found at onset of diabetes in only 4% of adults, but are universally present in diabetic children <4 years old at onset. The predictive value of both tests (ICA and IAA) is 60-77% in first-degree relatives of patients with IDDM for the development of IDDM in 5-10 years.

 <0.4 U/mL

In patients who have not yet been treated with insulin but have symptoms suggestive of diabetes or a genetic predisposition based on family history, this test can be used to 1) distinguish among type 1 diabetes mellitus (autoimmune), type 2 diabetes mellitus, and atypical forms of diabetes, such as latent autoimmune diabetes in adults (LADA); or 2) to evaluate risk of future type 1 diabetes. This test may also be useful when evaluating patients for very rare autoimmune hypoglycemic syndrome [1-3].

In patients who have already been treated with insulin, insulin autoantibodies are usually of no clinical significance. Therefore, insulin antibody testing is generally not indicated for these patients. However, in rare cases, patients with suspected type 2 diabetes who have failed hypoglycemic treatment are tested and subsequently diagnosed with type 1 diabetes [3]. This test is generally used along with other diabetes-related autoantibody tests such as GAD-65 Antibody (test code 34878) and IA-2 Antibody (test code 36177); all 3 antibodies can be ordered together as test code 10584. ZnT8 Antibody (test code 93022) may also be a useful additional test.

Testing for multiple diabetes-related antibodies may be helpful in diagnosis, because some forms of type 2 diabetes may initially resemble type 1 or have a positive result on testing for one of these autoantibodies [4]. The higher the number of autoantibodies that are positive, the higher the likelihood of an autoimmune cause (type 1 or LADA) for diabetes mellitus.

For patients who do not yet have clinically apparent diabetes, a higher number of positive autoantibody tests predicts a higher risk of developing type 1 diabetes in the future [1]. Rarely, insulin antibodies can take on a shape that resembles insulin closely enough to stimulate the insulin receptor, leading to hypoglycemia. The presence of insulin antibody in a hypoglycemic patient who has not previously been treated with insulin is suggestive of, but not definitive for, this rare syndrome [2].

Test results should be interpreted in the context of pertinent clinical and family history and physical examination findings.

References
1. Winter WE, et al. Clin Chem. 2011;57:168-175.
2. Censi S, et al. Ann Transl Med. 2018;6:335. doi: 10.21037/atm.2018.07.32
3. Pihoker C, et al. Diabetes. 2005;54(Suppl 2):S52-S61.
4. Wentworth JM, et al. Nat Rev Endocrinol. 2009;5:483-489.