Evaluation and Determination of the Sensitivity and Specificity of a Treponema Pallidum Dried Blood Spot Method for Serologic Diagnosis of Syphilis

EVALUATION AND DETERMINATION OF THE SENSITIVITY AND SPECIFICITY OF A Treponema pallidum DRIED BLOOD SPOT (DBS) METHOD FOR SEROLOGIC DIAGNOSIS OF SYPHILIS Background: Syphilis is a sexually transmitted infection (STI) caused by Treponema pallidum subspecies pallidum. Syphilis is known as the “great imitator" due to the similarity of clinical signs and symptoms to other infectious diseases. The primary diagnosis of syphilis relies on clinical findings, including the examination of treponemal lesions, and/or serologic tests. Serologic tests are divided into nontreponemal and treponemal tests. Nontreponemal tests are useful for screening, while treponemal tests are used as confirmatory tests. Methods: A total of 200 serum and DBS specimens collected from patients at the Los Angeles Municipal Sexually Transmitted Disease Clinics were tested by the DBS and enzyme immunoassay (EIA) methods. These samples were sent to the Syphilis Diagnostics Laboratory, Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia for testing. Samples were blindly evaluated by the TREP-SPOT TM DBS and the TREPSURE TM EIA methods for the detection of anti-treponemal IgGand IgM-class antibodies. Results: The sensitivity of the DBS method was 83% (95% CI, 73.89 89.50) and specificity was 100% (95% CI, 95.39 100)). The positive predictive value and negative predictive values were 100% (95% CI, 94.48 100) and 85% (95% CI, 77.43 91.0), respectively. The efficiency of the DBS method was 91.5%. The kappa value for the agreement between the DBS method and EIA assay was 0.83 (95% CI, 0.754 0.906). The correlation coefficient (r 2 ) between the antitreponemal antibody assay results obtained from DBS and serum samples was 0.94. Conclusion: DBS is an optimal choice to be used as a screening tool for the detection of anti-treponemal antibodies for the diagnosis of syphilis. The detection of anti-treponemal antibodies (TREP-SPOT TM DBS EIA) compared favorably to the results of serum-base assay (TREP-SURE TM EIA), with an overall concordance of 91.5%. Dried blood spots are technically easier to obtain and are suitable blood samples for primary health care centers.