The GAD Antibody Test
Reviewed by CDE Mehandi Sharma · Updated
The GAD antibody test is the single most important test in diagnosing LADA. It is an ordinary blood sample, sent to a laboratory.
GAD stands for glutamic acid decarboxylase, a protein found inside your beta cells. If your immune system has targeted those cells, it usually produces antibodies against GAD, and those antibodies can be measured in your blood.
A positive result means the damage to your insulin-making cells is autoimmune. That is the finding that separates LADA from Type 2 diabetes.
GAD antibodies are the most commonly found marker, but they are not the only one. Others sometimes tested are IA-2, ZnT8, insulin autoantibodies and islet cell antibodies. Testing positive for more than one usually means insulin-making capacity will decline faster.
The level matters too, not just the yes or no. Broadly, people with high antibody levels tend to be leaner, to have less insulin left, and to need insulin sooner. Those with low levels often look more like Type 2 diabetes and progress more slowly.
If GAD is positive, the next question is how much insulin you are still making — which is what the C-peptide test answers.