Certain HLA alleles are used as diagnostic aids to help determine if individuals will be more susceptible/predisposed in their lifetime of developing certain conditions or are used in correlation with other clinical findings and tests to determine if someone is to be diagnosed with a certain disease. Table 3 provides several examples.
Table 3. HLA Alleles and Predisposition to Diseases.| Disease | Characteristics | Associated HLA Allele(s) |
| Ankylosing Spondylitis (AS) | Rare disease that causes arthritis in the lower spinal column and vertebrae to fuse, forming a rigid spine | B27 |
| Celiac disease (CD) | Autoimmune disease where the individual has a sensitivity to gluten | DQA1 and DQB1 95% of CD patients have DQ2 (DQA1*05 and DQB1*02) |
| Diabetes Mellitus (DM) | Disease in which the body fails to respond to the hormone insulin, which is produced by the pancreas | DRB1, DQA1, DQB1: DRB1*03:01 (DR3) w/ DQA1*05:01, DQB1*02:01 (DQ2) AND DRB1* 04:01 (DR4) with DQA103:01, DQB1*03:02 (DQ8) |
| Narcolepsy | Neurological disorder characterized by the inability to control sleep and wakefulness | DQA*01:02, DQB1* 06:02, and DR15 |
| Psoriasis | Immunological disorder that is brought on by illness, stress, or infection and is characterized by rashes on the skin and nails | Cw6 |
| Drug reactions | Certain HLA alleles have been correlated to an increased risk of hypersensitivity with certain drugs | Reactions and hypersensitivities exist between carbamazepine and abacavir with HLA alleles B*15:02 and B*57:01 |
