VDRL Test and its Interpretation

Abstract

Sir, We read with great interest the CME article titled “VDRL ttest and its interpretation,” which was published in March 2012 (2012; 57(1): 3-8) issue of Indian Journal of Dermatology.[1] The article very clearly and rightly conveyed the facts and misconceptions about this test and its interpretations in pregnant women and in cases of congenital syphilis, neurosyphilis and HIV infection. Interpretation of the VDRL test in congenital syphilis was specially excellent as it suggested that all infants born to mothers who have reactive non-treponemal and treponemal tests results should be evaluated with a quantitative RPR/VDRL test performed on infant's serum and not on cord blood. Infection in the infant is indicated when the infant's antibody titer is higher than that of the mother and it is shown to rise. Testing of IgM treponemal antibody is not sufficiently reliable to diagnose congenital syphilis.[2] However as microbiologists we would also like to clarify the following points:- The three basic methods (dark ground microscopy, non-treponemal and treponemal serological tests) are in use for diagnosis of syphilis and not in screening for syphilis. However, the testing strategy for syphilis varies depending on whether the aim is to detect all stages of syphilis or only infectious syphilis. In the United States (US), some European countries and India, only non-treponemal tests are used for screening.[3] The non-treponemal tests - VDRL/RPR - are both flocculation tests but are not modification of original Wasserman reaction. Wasserman reaction is a complement fixation reaction and not a flocculation test. The result of the VDRL/RPR is read as reactive or non-reactive and not as positive/negative. Although this has been made clear by the authors themselves but at number of places in the interpretation part of the article, the test results have been mentioned as positive or negative. If the test is reactive, it is quantified and the lowest dilution (last dilution i.e., titer) at which the test result is reactive is given as final result. Quantitative tests establish a baseline of reactivity from which change can be measured. Recent infection can be demonstrative as a four-fold rise in titer and re-infection and relapse as persistently reactive (serofast) test result.[3] In “conclusions” in the article, it has been mentioned that Treponema pallidum is not easily cultured and cannot be grow on artificial media. In fact, T. pallidum has never been cultured continuously on artificial media or in fertile eggs or tissue cultures. Of the various animals, rabbits can be infected in the skin, testes and eye, although no progressive disease is produced.[4]