Blood tests in Inflammatory Arthritis

Blood tests in Inflammatory Arthritis

·        Gout and seronegative arthritis are not normally positive for rheumatoid factor and auto-antibodies

·        Rheumatoid Factor: IgM against Fc portion of IgG. Can be tested with the Rose-Waaler titre. Positive in:

o   70-80% of RA

o   < 40% of SLE

o   100% of Sjogren‟s

o   30% of PSS

·        ANA: Autonuclear Antigens

o   Screening test of SLE: present in > 95% at titre > 1:200 – but not specific

o   Present in RA (30%), Sjogren‟s (68%), PSS (64%), and normal (0 – 2%)

o   Also ­ with age, other autoimmune diseases, drugs, infections

o   Patterns:

§  Diffuse ANA suggests dsDNA may be +ive

§  Speckled ANA suggests ENA may be +ive

§  Anti-DNA histone: suggests active SLE.  Also in 95% of drug SLE

§  Anti-centromere: suggests systemic sclerosis

·        dsDNA: 70% of SLE. Specific (ssDNA is not). Titres correspond to clinical activity and risk of nephritis

·        ENA: Extractable Nuclear Antigens (not all speckled ANA results are due to ENAs):

o   Anti-Ro (SSA): Sjogren‟s, SLE (30%)

o   Anti-La (SSB): Sjogren‟s.  Always associated with SSA.  Found in only 10% of SLE

o   Anti-Sm: 30% of SLE.  Specific

o   Anti-RNP: SLE (40%), polymyositis, scleroderma, mixed disorders

o   Anti Jo-1: polymyositis and dermatomyositis

·        Anti-phospholipid antibodies (attacks phospholipid on platelets)

o   Occurs in 50% of SLE.  Do Lupus anti-coagulopathy test

o   3 types:

§  Lupus anticoagulant:  Causes ­APTT, but causes thrombosis in vivo

§  Anti-cardiolipin

§  False positive VRDL test

§  1 and 2 associated with fetal loss, clotting, thrombocytopenia, valvular heart disease 

o   Antiphospholipid Syndrome: recurrent miscarriages, thrombocytopenia and recurrent arterial or venous thrombosis

·        ANCA: Associated with some small vessel vasculitis. Can divide arteritis into ANCA +ive and –ive (although pANCA may also be found in 20% of polyarteritis nordosa): 

o   Cytoplasmic anti-neutrophil cytoplasmic antibody (cANCA): Specific but not sensitive for

o   Wegener‟s disease > 90% +ive 

o   Perinuclear anti-neutrophil cytoplasmic antibody (pANCA): Microscopic polyangitis ~ 75% (vasculitis in kidney and lung) and PAN

o   ANCA negative small vessel vasculitises include Henoch-Schonlein Purpura

·        CD4+:CD8+ ratio (normally ~3) ­ in Polymyalgia Rheumatica