GAD-65 autoantibodies
The single most useful autoantibody to distinguish autoimmune (type 1, LADA) from non-autoimmune (type 2, MODY) diabetes. Positive titres + low C-peptide is the textbook adult-LADA signature.
What it measures
Glutamic acid decarboxylase 65 (GAD-65) is an enzyme found inside pancreatic beta cells. In autoimmune diabetes, the immune system mistakenly produces antibodies against it — a fingerprint of the same process that's destroying the beta cells themselves. GAD-65 antibodies are present in ~80% of adult-onset type 1 diabetes (often diagnosed as 'LADA' — latent autoimmune diabetes of adults), ~70% of classical childhood-onset type 1, and only a few percent of true type 2 diabetes. The test is ordered when the type of diabetes is clinically ambiguous, when a lean adult presents with high glucose but doesn't behave like type 2, or when family screening is requested.
What a high value can mean
- Type 1 diabetes (classical, childhood-onset) — ~70% positive.
- LADA (adult-onset autoimmune diabetes) — ~80% positive; presents like type 2 but progresses to insulin requirement within months to years.
- Stiff person syndrome — rare neurological disease with very high titres (>2000 IU/mL).
- Cerebellar ataxia, limbic encephalitis — neurological GAD-associated syndromes (also very high titres).
- Autoimmune polyendocrine syndrome — co-clusters with Hashimoto's, Addison's, vitiligo.
What a low value can mean
- Type 2 diabetes — typical pattern: negative GAD + preserved C-peptide.
- MODY (monogenic diabetes) — negative GAD; genetic testing required.
- Steroid- or drug-induced hyperglycaemia.
When to discuss with a doctor
Order GAD-65 when the diabetes type is unclear — lean adult with new hyperglycaemia, family history of autoimmunity, atypical response to oral agents, or paediatric presentation. A positive result + low C-peptide changes the treatment plan to insulin earlier rather than later, and triggers screening for other autoimmune conditions (thyroid, adrenal). Very high titres (>2000) flag the rare neurological GAD syndromes — refer neurology. Mediora.AI shows GAD-65 alongside C-peptide so the autoimmune-vs-insulin-resistant pattern is visible at a glance; the diabetes-type decision is endocrinology.