Sunday, August 23, 2015

Leukocyte esterase does not help in the diagnosis of shoulder periprosthetic joint infection

These authors proposed that leukocyte esterase (LE) would be useful in the diagnosis of shoulder periprosthetic joint infections. They evaluated: 45 primary and 40 revision shoulder arthroplasties. Synovial fluid and soft tissue cultures were obtained at surgery. Synovial fluid was evaluated with LE test strips.

At least 3 sets of intraoperative cultures were collected. Anaerobic, aerobic, acid-fast bacilli, and fungal cultures were performed, although the specimen collection and culturing protocols were somewhat variable especially for the primary arthroplasties.

The culture results for the 40 revision arthroplasties were as shown below

Of 5 primaries with positive tissue cultures (11%), only 1 was positive for LE. 
Of 16 revisions with positive cultures (40%), 4 had positive LE results. 

Among all patients with bacterial isolates, 6 aspirates were not interpretable (29%), despite centrifugation. 

LE had sensitivity of 25% and specificity of 75% to predict positive cultures in revisions.

The authors concluded that leukocyte esterase is an unreliable diagnostic measure in shoulder PJI. The presence of erythrocytes within aspirates further decreased its accuracy.

Comment: The authors are to be congratulated in presenting a negative result! Prior posts have shown that synovial interleukin-6 (IL-6) and alpha defensin are of marginal benefit in making the diagnosis of perioprosthetic shoulder infection. Once more it is of interest that 40% of the revisions were culture positive and that Propionibacterium was the most common bacteria cultured.

This result is not unexpected in that infections with Propionibacterium do not stimulate a neutrophilic response: histology rarely shows an increase in the number of white cells per high power field.

The takeaway is that revision arthroplasties should be considered to contain bacteria until the results of properly done cultures prove that this is not the case.


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