A comparative analysis of VDRL, RPR, Immutrep TPHA and Instachk TP

INTRODUCTION Syphilis is a systemic infectious disease caused by Treponema pallidum which can lead to irreversible lifelong sequelae if left untreated. Diagnosis of syphilis today mainly depends on serological assays each of which have their own pitfalls. Hence it is essential to evaluate the present day serological diagnosis of syphilis and to compare their effectiveness in diagnosis. AIM To compare RPR, VDRL, Immutrep TPHA and Instachk TP MATERIALS AND METHODS This prospective cohort study was done during the period of Dec 2010 to June 2011. Serum samples from four hundred and fifty patients were obtained from STD department and antenatal clinic and they were subjected to RPR, VDRL, Immutrep TPHA and Instachk TP. RESULTS Overall positivity rate of serological tests in the detection of syphilis was VDRL (90.56), RPR (79.25), TPHA (100) and Instachk TP (100). VDRL was able to detect 6 cases of low titres more frequently than RPR. RPR was one titre less than VDRL in eight cases. Instachk TP was as specific as TPHA but the results can be interpreted within 15 minutes and can be done at field level. CONCLUSION VDRL detects low titres more frequently than RPR.VDRL and RPR should not be interchanged during follow up of patients and in external quality assessment. Among the specific tests, the Instachk test is a rapid test that can be interpreted within minutes. This can open up new avenues for early, rapid and accurate detection of syphilis at a field level. So the present day serological tests of syphilis can thus be limited to the specific tests to exclude syphilis and the nonspecific tests to judge the need or effectiveness of antisyphilitic treatment.