Investigations : Following investigations are useful:1) Radiological examination: X-rays of the affected joints and X-rays of both hands ➨Reduced joint space
➨Erosion of articular margins
➨ Subchondral cysts➨Juxta-articular rarefaction
➨ Soft tissue shadow at the level of the joint because of joint effusion or synovial hypertrophy ➨Deformities of the hand and fingers2) Blood: It shows the following changes:• Elevated ESR • Low haemoglobin value 
• Rheumatoid factor (RF): This is an auto antibody directed against the Fc fragment of immunoglobulin G (IgG). RF can belong to any class of immunoglobulins i.e., IgG-RF, IgM-RF, IgA-RF, or IgE-RF, but commonly done tests detect only the IgM type of RF. It can be detected in the serum of the patient by the following tests:
• LATEX FIXATION TEST: This is an agglutination test where the antibodies are coated to latex particles. Positivity in titres more than 1/20 is significant. Sensitivity is 80 per cent.
ROSE-WAALER TEST: In this agglutination test sheep red blood cells are used as a carrier.Sensitivity is 60 per cent.All patients with positive rheumatoid factor do not have rheumatoid arthritis.Conversely, all patients with rheumatoid arthritis do not have a positive rheumatoid factor. It is the cluster of signs and symptoms, concentration  in which the RF is positive, presence or absence of other positive tests, etc, which determine whether the patient has rheumatoid arthritis or not.
Synovial fluid examination–
Synovial biopsy: open methods this can be obtained arthroscopically .

➽DIFFERENTIAL DIAGNOSIS
Rheumatoid arthritis must be differentiated from the following diseases:a) Systemic lupus erythematosus (SLE): In SLE, the joint involvement is not symmetrical, nor are ankylosis and erosions common. (ANF) Absence of anti-nuclear antibody factor is in favour of rheumatoid arthritis, although its presence does not confirm Systemic lupus erythematosus. It is present in 25%  cases of rheumatoid arthritis, though in low titres.
b)Osteoarthritis: This occurs in older patients.There is complete lack of the systemic features of rheumatoid arthritis such as,weight loss, fatigue  fever etc. DIP joint are often involved.Time of  joint swelling, ESR ,morning stiffnessetc., are less compared to rheumatoid arthritis.
c) Psoriatic arthropathy: Characteristic nail and skin lesions may be present. Distal inter phalangeal joints are usually involved.Rheumatoid factor is negative.

Prognosis: Following factors decide the outcome of a patient diagnosed to have rheumatoid arthritis

➼Natural history of the disease: It is well known that rheumatoid arthritis is a disease with variable natural history. It may be fulminant ie., damaging joints quickly and producing deformities in spite of best care, or more usually a disease with persistent course punctuated with remissions and exacerbations.
➼Sex and age at onset: Women of child bearing age with predominant upper extremity involvement have a progressively severe disease. Males, with sparing of upper extremity, where onset of disease is under the age of 30 years, show less severe disease.
➼ Type of onset: It is generally believed that insidious onset disease progresses to have more severe disease.
➼Anaemia: Anaemia is associated with progressive rheumatoid arthritis. Also, it is believed that unresponsiveness of anaemia to oral iron therapy is a bad prognostic indicators.
➼ ESR and C-reactive protein: High levels are associated with more erosive arthritis.

➼ Rheumatoid factor: A positive rheumatoid factor is associated with more progressive disease. High consentration of rheumatoid factor, appearing early in the disease, hold a bad prognosis
➼Radiological erosions: Presence of erosions within 2 years of onset of the disease, is a bad prognostic indicator
➼Histopathological changes: A case with synovial proliferation, with increased number of synovial cells with DR antigen, carries bad prognosis.