Synovial Fluid Analysis

Cell Counts x 106/L

 

Done by a grid system per HPF

- x40

- averaged over 10 fields

 

Normal

- 0-200

 

Non Inflamm (Trauma / OA)

- 50 - 500

 

Inflamm (RA / Crystals)

- 1500 - 50 000

 

Infection

- > 50 000

- exception is gonococcal arthritis

 

Different Units

 

Standard now SI Units 10 x 106/ L  

= 10 cells / mm3

= 10  x  103 /ml 

= 10  x  103 /cc

= 10  x  105 /dl

= 10  x  105 /100ml

= 10  x  106 / L

 

Cell Differential

 

Polymorph % 

- normal 0-25 %

- non inflammatory = 0- 25 %

- inflammatory = 30- 70 %

- infection  > 75 %

 

Viscosity

- will decrease as inflamation increases

- effect of hyluronate lost

- hence sepsis = Low viscosity

 

Additional

 

Glucose < BSL

 

± Crystals as acid Ph decreases solubility

- presence of crystals does not exclude infection

 

Gram stain positive 30%

Culture positive 60%

 

Weinstein

 

WCC > 50,000 + > 90% PMN leukocytes

- should be considered infectious regardless of the culture results 

 

Fink Clin Rheum Dis 1986;12:423. 

- large series of culture-proven cases of bacterial septic arthritis

- only 44% had cell counts > 100,000 per mm3

- 34% of cases having counts of < 25,000 per mL