Lab Case 79 Interpretation

72 year old with painful monoarthritis and signs of inflammation. Infection must be excluded.

  1. Causes:

Inflammation – septic (viral, bacterial, gonococcal), gout, pseudogout, RA (monoarticular), systemic rheumatic disorders ( SLE, still, reactive arthritis, Behcets, bacterial endocarditis, Rheumatic fever etc)

Non Inflammatory – OA, trauma, haemarthrosis, osteonecrosis

2. Pseudogout without superimposed infection

3. Normal synovial fluid contains < 60 to 180 cells per ml, most of which should be mononuclear. Fluid is considered to be “noninflammatory” if it contains < 2000 cells / ml. Finding of > 90% PMNs despite relatively low total leukocyte count should prompt concern about infection or crystal-induced disease. Using a 50000 cutof for leucocytes lacks the sensitivity required to be clinically useful in ruling out infectious arthritis.


  Gout Pseudogout
History/ Co morbidities Malignancy


Myeloproliferative disorders

Medication – diuretics

Previous attacks


HyperPTH, Hypothyroidism

HypoMg, HypoPO4


Usually no previous attacks


Examination Painful, swollen, inflamed joint

Monoarticular (<5 joints)


Painful, swollen, inflamed joint

Gouty tophi

Monoarticular is usual

Bloods High Ca

Low Mg, PO4

Low T3/ high PTH

Uric acid high/ normal
Synovial fluid Uric acid crystals

-ve birefringent – polarised light

Larger, needle shaped crystals

Blue if parallel to light

Yellow if perpendicular

CapyroPO4 crystals

+ve birefringent

Smaller, rhomboid/ needle shaped crystals

Yellow if parallel

Blue if perpendicular

Radiology Calcifications may be visible No calcifications

Gouty erosions

Sclerotic margins


Treatment Analgesia

Gout treatment

Look for cause

Aspirate joint +/- steroid injection


Look for cause