Lab case 417 interpretation


Volume = 15 ml. Still significant, Normal amount of synovial fluid in a knee joint is 0.5 to 4 mls. Knee joint can accommodate volume to about 100 ml.

Colour is transparent yellow. Normal synovial fluid colour is clear and transparent. It turns yellow in non-inflammatory and inflammatory joints effusion. In gout arthritis the colour is usually milky yellow, in Rheumatoid arthritis the colour is yellow to green. While is septic arthritis the colour is described as dirty yellow (Closer to grey than yellow). As discussed in last week case.

Cell count 18700, that is high. However, not high enough for septic arthritis. Normal cell count in synovial fluids is less than 200 cells per cubic mm. This number will go up to less than 2000 in non-inflammatory joint effusions. Levels more than 2000 are usually inflammatory and for septic arthritis, usually WBC count is more than 50,000 per cubic mm.

However, this patient had 2 courses of antibiotics and that might alter these results.

Polymorphs ratio = 78%, that is very significant and it fits within the range of septic arthritis. (>75%).

Based on the symptoms and theses synovial fluid results, this patient has either:

  • Reactive arthritis
  • Partially treated gonorrhoeal arthritis.

Treatment starts with urethral swabs (To check for chlamydia and gonorrhoea). Then treat as gonorrhoea until the swab results are back.