Objective: To determine the usefulness of reagent test strips for screening inflammatory synovial fluid (SF).
Methods: Consecutive patients undergoing diagnostic arthrocentesis, attending the Department of Rheumatology of a large tertiary care hospital were evaluated. All SF specimens obtained were tested using two techniques: (i) white blood cell (WBC) count with the differential according to standard practice (which is considered the gold standard) (an inflammatory SF was defined as a WBC count > or =2000 cells/mm3); and (ii) reagent strips used to test urine (Multistix 8 SG, Bayer Diagnostics) for the presence of leucocytes (a positive test was defined as a strip showing more than a trace for leucocytes). Sensitivity, specificity, predictive values and likelihood ratio (LR) of the reagent strip in diagnosing inflammatory SF were determined.
Results: Two hundred and eight samples of SF were tested. The results of using the reagent strip were: sensitivity 76.9% (95% CI, 66.0-85.7%), specificity 86.9% (95% CI, 79.9-92.2%); positive LR, 5.88 (95% CI, 3.71-9.31) and negative LR, 0.27 (95% CI, 0.18-0.40). In 13 of the 19 false negative results, the differential cell count showed a predominance (> or =50%) of lymphocytes.
Conclusion: This study suggests that, in daily practice, the evaluation of SF by reagent strips could be of use to discriminate between inflammatory and non-inflammatory SF.