Abstract
Although there is still no absolute diagnostic test for infection of the prosthetic joint, the synovial fluid leukocyte count and neutrophil percentage have been reported as having high sensitivity and specificity but to date the cut off values for these tests are not agreed upon. We investigated whether leukocyte count and differential of aspirated joint fluid are valuable tools in the diagnosis of suspected prosthetic joint infection.
In 39 patients who underwent revision arthroplasty the cell count and differential of joint aspirates were cross-referenced with culture results and histology to confirm that these were valid tests and to determine cut off values. Cases were identified via the microbiology service of two district general hospitals: 17 patients in whom infection was identified via culture and/or histology results and 19 who were uninfected.
Receiver operator characteristic curves were used to determine the correlation between the results of the two tests and to identify a suitable threshold level. For absolute leukocyte count the area under the curve was 0.997 indicating excellent agreement between the tests. A cut off value of 2000 gave a sensitivity of 100% and a specificity of 94%. Differential count had an area under the curve of 0.94. A threshold of 50% had a sensitivity of 100% and a specificity of 77%.
Despite the low number of patients this study shows that the leukocyte count and differential of aspirated joint fluid are valuable tools in the diagnosis of suspected prosthetic joint infection.
