Joint size influence on the leucocyte count of inflammatory synovial fluids

The mean leucocyte count (LC) of the synovial fluid (SF) obtained from 22 elbow joints of patients with chronic inflammatory polyarthritides was 23.4 +/- 17.8 x 10(9)/l while the mean LC of the SF from their paired larger knee joints with similar degree of clinically detectable inflammation was 10.9 +/- 9.9 x 10(9)/l (p less than 0.001). The mean of the ratios between the LC of the paired joints (LC elbow/LC knee) was 2.92 +/- 2.07, above the ratio 1.0 (p less than 0.001) which would be expected if the LCs of both joints were similar. Different sizes of the paired joints presumably explained the phenomenon, which may be due to dilution factors. The size of the joint should be considered when interpreting the leucocyte counts of synovial fluid.