Centrifugation May Change the Results of Leukocyte Esterase Strip Testing in the Diagnosis of Periprosthetic Joint Infection.

BACKGROUND

Centrifugation is used to remove the color interference by erythrocytes in blood-synovial fluid samples before leukocyte esterase (LE) strip testing. However, the impact of centrifugation requires further study.

METHODS

From April 2016 to October 2017, 133 (53 infected and 80 noninfected) patients were included in this study. One drop of synovial fluid was applied to LE strips before and after centrifugation in 110 cases. The other 23 cases could not be read without centrifugation due to the color disturbance caused by blood contamination. The results were recorded after approximately 3 minutes according to different color grades on a color chart, including grade 3 (++), grade 2 (+), and grade 1 (others).

RESULTS

After centrifugation, almost every sample was lighter in color than before. Although most results changed inconspicuously and remained in the same grade, 18.6% (8/43) and 17.9% (12/67) of cases were downgraded in the periprosthetic joint infection and non-periprosthetic joint infection groups, respectively. Before centrifugation, when grade 3 (++) was used as the positive threshold, the sensitivity and specificity were 97.7% (86.2%-99.9%) and 100% (94.3%-100%), respectively. After centrifugation, when grades 2 and 3 (+ and ++, respectively) were used as the positive threshold, the sensitivity and specificity were 92.5% (80.9%-97.6%) and 100% (94.3%-100%), respectively.

CONCLUSIONS

The influence of centrifugation should be considered when interpreting the LE strip test results. For cases without centrifugation, we recommended using ++ as the positive threshold, while for cases using centrifugation, the threshold should be reduced to both ++ and +.