Rapid diagnosis of inflammatory synovial fluid with reagent strips

Abstract

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 ≥ 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 (≥ 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.