Equis ISSN 2398-2977

Synovial fluid: cell count

Synonym(s): Joint fluid

Contributor(s): Prof Derek Knottenbelt

Overview

  • Synovial fluid   Synovial fluid: normal finger test  is a dialysate of blood and normally has a low white cell count (0.2-0.9 x 10*9/l) predominantly mononuclear cells, minimal erythrocytes and high viscosity due to glycosaminoglycan content.
  • Inflammation and to a lesser extent degenerative or traumatic conditions decrease the viscosity of synovial fluid.
  • A differential white cell count will help distinguish inflammatory from non-inflammatory conditions.
  • See also:

Sampling

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Tests

Methodologies

Viscosity
  • Normal synovial fluid forms a small globule on slide or in tube.
  • Subjective assessment of the length of string formed by allowing fluid to drop from the needle tip.
    Cell count
  • By electronic or hemocytometer chamber methods.
  • Use isotonic saline as dilution fluid.
    Glacial acetic acid, often contained in white cell dilution fluid, can cause synovial fluid to clot and confuse the count
  • Can estimate white cell count by comparing the average number of white cells per field with that of a blood specimen with a known count.
  • An estimate of normal, mildly, moderately or greatly elevated may be satisfactory. Normally 2 cells per 40x magnification field in body of smear.
  • Differential cell count compares polymorphonuclear with mononuclear counts.

Availability

  • Can be performed in practice laboratory.

Technique (intrinsic) limitations

  • When counts are moderately elevated and differentials unremarkable, may not be able definitively to separate degenerative from immune-mediated conditions.
  • Contamination with blood may obscure true white cell count.

Result Data

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Further Reading

Publications

Refereed papers

Other sources of information

  • McIlwraith C W & Trotter G W (1996) Eds. Joint Disease in the Horse. W B Saunders, USA.


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