Lab case 416 interpretation


Volume of 25 ml is large, normal amount of synovial fluid in a knee joint is 0.5 to 4 ml. This indicates effusion. The knee joint is one of the largest joints in the body and it can accommodate around 100 ml of synovial fluids in cases of massive severe effusion.

That tells us that there is abnormal amount of fluid in the joint but it doesn’t help in detecting the cause.

Colour: Turbid 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).

In this case, the colour might be indicative of gout or early septic arthritis.

Leukocyte count: 45890, This number is far from non-inflammatory causes. (Usually less than 2000).

Inflammatory causes include:

  •  Rheumatoid arthritis
  • SLE
  • Reactive arthritis
  • Gout
  • TB
  • Fungal

In these cases WBC count is between 2000 and 50.000  (In some resources it is up to 75.000).

While in septic arthritis, WBC count is usually more than 50.000 (In some resources is more than 60.000).

However, gouty arthritis can show count more than 60000.

Polymorph count of 94% (Ratio of 94 to 6), That is very suggestive of septic arthritis. In almost all the resources, they agree that PMN cells ratio of more than 75% should be considered as septic.

Even if this patient’s synovial fluid showed crystals, the condition should be treated as septic arthritis.

Patient’s with gout arthritis has increase tendency for septic arthritis.