Diagnosis reported as exclusion criteria and baseline investigations undertaken prior to inclusion as UPIA (ordered by the frequency of reporting in the retrieved literature), both in studies including patients exclusively with UPIA as well as in selected mixed populations that included a well-defined subset of patients with UPIA
| A. Reported differential diagnosis prior to establishing the operational diagnosis of UPIA | |
| - Rheumatoid arthritis | - Polymyalgia rheumatica |
| - Osteoarthritis | - Lyme disease |
| - Spondyloarthritis (reactive arthritis, psoriatic arthritis, ankylosing spondylitis and undifferentiated spondyloarthritis) | - Vasculitis |
| - Crystal-related arthritis | - Juvenile inflammatory arthritis |
| - Trauma | - Palindromic rheumatism |
| - Connective tissue diseases (systemic lupus erythematosus, Sjögren syndrome and myositis) | - Fibromyalgia |
| - Septic arthritis | - Endocrinological origin |
| - Sarcoidosis | - Malignancy-related arthritis |
| - Soft tissue disorders | - Viral aetiology |
| B. Reported investigations prior to establishing the operational diagnosis of UPIA | |
| - History | - Microbiological assessment |
| - Tender and swollen joint count | - Anti-citrullinated protein/peptide antibodies |
| - Rheumatoid factor | - Radiography of the chest and/or of other affected joints |
| - C reactive protein | - Urinalysis |
| - Physical examination | - Thyroid function tests |
| - Hands and feet x-rays | - C3, C4 |
| - Full blood count | - Immunoglobulins |
| - Antinuclear antibodies | - Antibodies to extractable nuclear antigens |
| - Erythrocyte sedimentation rate | - Antibodies to double-stranded DNA |
| - Biochemistry (liver function tests, glucose, urate and renal function) | - Specific serological assessment |
| - HLA typing (HLA-B27 and HLA-DR) | |
UPIA, undifferentiated peripheral inflammatory arthritis.