Common Sense Pathology

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Initial laboratory investigation

Careful clinical assessment.  Clinical manifestations of arthritis are seldom sufficiently specific to permit a precise diagnosis without the aid of diagnostic imaging and laboratory tests. These contribute to diagnosis, assessment of severity and complications, monitoring of disease activity and drug therapy. FBC, CRP or ESR Protein electrophoresis.  ANF and rheumatoid factor Joint aspiration may be indicated, especially  those with monoarthritis: synovial  fluid examination with tests as  appropriate to the clinical context and includes:

  • Gross appearance
  • Performing a cell count and Gram's stain
  • Examination for crystals 
  • KOH preparation and stains for AFBs especially in chronic monoarthitis
  • Culture
  • Gonococcal PCR, in culture negative infective arthitis

Synovial biopsy, if indicated.



Infectious  Bacterial  Septic arthritis Bacterial endocarditis  Lyme disease Fungal and mycobacterial Viral

Blood and synovial fluid for microscopy and  culture  Blood culture  Lyme serology  Synovial fluid for fungal / mycobacterial culture Synovial biopsy for culture and histology  Coxsackie B serology Rubella serology HbsAg serology  EBV serology Parvovirus B19 serology HIV serology


In the acute phase, microbiological studies may be useful to identify the precipitating infection Faeces - microscopy, culture and antigen detection (Salmonella, Shigella,  Campylobacter, Yersinia spp.) Genital (urethral or cervical) swab for MCS Urine for chlamydia PCR and/or gonococcal  PCR Chlamydia trachomatis antibodies

Rheumatic fever

ASO titres Throat swab for culture of Streptococcus  pyogenes FBC, ESR, CRP

Reiter's syndrome


Inflammatory bowel disease


Rheumatoid arthritis; Still's disease

Rheumatoid factor Synovial biopsy, if indicated FBC, ESR, CRP

Systemic rheumatic disorders (Connective tissue diseases)

Rheumatoid factor Antinuclear (ANF) and extractable nuclear antigen (ENA) antibodies

Rheumatoid arthritis SLE

Complement C3 and C4. Synovial biopsy, if indicated

Crystal induced  Gout  Pseudogout

Examination of joint fluid for crystals Serum uric acid 

Others Seronegative arthritis 

Rheumatoid factor-negative spondylo- arthropathies associated with HLA-B27.

Ankylosing spondylitis  Psoriatic arthritis

Serum HLA-B27

Trauma Degenerative joint disease

Synovial fluid examination



  1. Harrison 's Principles of Internal Medicine. 12th edition. pp 544 - 548, and pp 1453 - 1455
  2. Baker DG, Schumacher HR. Acute monoarthritis. NEJM 1993; 329: 1013 - 1020
  3. Pinals RS. Polyarthiris and fever. NEJM 1994; 330: 769 - 775
  4. Ward MM. Laboratory testing for systemic rheumatic diseases. Postgrad Med 1998; 103: 93 - 100
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