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Chapter 8: Clinical 353

Investigations and procedures of patients with rheumatoid arthritis have IgM rheuma-
toid factor; however, it may also be detected in a number
Laboratory investigations of other conditions. Seropositivity allows prediction of
severity and the need for earlier aggressive therapy and
Although some of the available tests used in diagnosis
increases the likelihood of extra-articular features.
of rheumatological conditions are diagnostic, most have
Antinuclear and anticytoplasmic antibodies: Antibod-
limited value as they may be present in multiple condi-
ies against multiple cellular components have been char-
tions (non-specific), or they may only be present in some
acterised and may be detected.
ofthepatientswiththedisease(non-sensitive).Combin-
ing tests may allow a clinical diagnosis to be confimed Joint aspiration
(see Table 8.1).
Rheumatoid factor: These are antibodies of any class Unexplained joint swelling may require aspiration to
directed against the Fc portion of immunoglobulins. aid diagnosis. The aspiration itself may be of therapeu-
The routine laboratory test detects only IgM antibodies, tic value lowering the pressure and relieving pain. It is
which agglutinate latex particles or red cells opsonised often coupled with intra-articular washout or instilla-
with IgG. It is the presence of these IgM rheumatoid tion of steroid or antibiotic as appropriate. Examina-
factor antibodies that is used to describe a patient as tion of the synovial fluid may be of diagnostic value (see
seropositive or seronegative. Seventy to eighty per cent Table 8.2).

Table 8.1 Antibodies detectable in rheumatological conditions
Antibody type Antigens Condition associations
Antinuclear antibodies Double stranded DNA SLE highly specific
Centromere Systemic sclerosis
High titre speckled pattern Suggests antibodies to extractable nuclear antigens
Extractable nuclear Ro (SSa) Sj ¨ogren’s syndrome
antibodies Systemic lupus erythematosus
La (SSb) Sj ¨ogren’s syndrome
Systemic lupus erythematosus
Sm Systemic lupus erythematosus
Ribonuclear protein High in various connective tissue disease and overlap syndromes

Others Jo-1 (histidyl tRNA synthetase) Polymyositis with pulmonary fibrosis
Scl 70 Scleroderma
Antineutrophil cytoplasmic cANCA (proteinase 3) Wegener’s granulomatosis
antibodies pANCA (myeloperoxidase) General vasculitis, inflammatory bowel disease

Table 8.2 Synovial fluid analysis

Fluid Normal Non-inflammatory Inflammatory Septic
Colour Straw Straw yellow Off white Variable
Clarity Clear Clear Opaque Opaque
Viscosity High High Low Variable
WCC number <200 200–2000 3000–75,000 >50,000
% PMN <25 <25 >50 >90