Asian Journal of Transfusion Science
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LETTER TO THE EDITOR Table of Contents   
Year : 2015  |  Volume : 9  |  Issue : 1  |  Page : 109
Rapid plasma reagin test: High false positivity or important marker of high risk behavior


Department of Blood Bank, Dr. Ram Manohar Lohia Hospital, New Delhi, India

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Date of Web Publication6-Feb-2015
 

How to cite this article:
Arora S, Doda V, Rani S, Kotwal U. Rapid plasma reagin test: High false positivity or important marker of high risk behavior. Asian J Transfus Sci 2015;9:109

How to cite this URL:
Arora S, Doda V, Rani S, Kotwal U. Rapid plasma reagin test: High false positivity or important marker of high risk behavior. Asian J Transfus Sci [serial online] 2015 [cited 2019 Oct 14];9:109. Available from: http://www.ajts.org/text.asp?2015/9/1/109/150979


Sir,

As per the national guidelines, all the donated blood should be mandatorily tested for HIV I and II virus, hepatitis B virus, hepatitis C virus, malaria, and syphilis. Screening of the donated blood for syphilis is carried out either by rapid plasma reagin (RPR) or venereal disease research laboratory in the blood banks. During the period from January to August 2013, a total of 9100 donors were screened for syphilis by RPR (Span Diagnostics Ltd.) at our blood bank. Initial RPR reactive samples were further titrated by doubling dilutions of the samples with physiological saline (0.9%), as per the manufacturer's instructions for semi quantitative RPR. Confirmatory testing by treponema pallidum hemagglutination assay (TPHA) for all initially RPR reactive undiluted samples was done to ascertain the true positivity.

Among 9100 donors screened for syphilis, 20 donors were found to be reactive by RPR. Of 20 reactive donor samples, only 8 were confirmed on the supplementary testing (TPHA) indicating overall 40% true positivity of the initial RPR reactive samples. [Table 1] Of these 12 TPHA nonreactive but RPR reactive, hepatitis B virus (HBV) DNA was incidentally detected in two samples. One of them was both enzyme-linked immunosorbent assay [ELISA] and ID-nucleic acid test [NAT] reactive) while the other was NAT yield of HBV (ELISA-nonreactive, ID-NAT- reactive).
Table 1: Details of semi quantitative analysis (titration) done on initial RPR reactive samples

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Nontreponemal antigen tests (RPR), are designed to test serum for reagin, a heterogeneous group of antibodies, which combine with a cardiolipin-lecithin antigen. This antigen, usually derived from beef heart and is a normal component of human tissue. Because cardiolipin (which mimics treponemal antigens) is used, approximately two-thirds of "reactive" samples during testing can have cross-reactivity and are"biological false-positives." [1] These BFP can be either due to other type of pathogenic treponemal infections or a strong immunological stimulus [2],[3] e.g., acute bacterial or viral infection, vaccination, etc.

One of the study [4] from western region of our country showed 56.4% false positivity of RPR in blood donors as compared with 60% in our study further indicating impact of RPR on the discard rate of the blood bank.

Treponemal tests (TPHA) detect an antibody that is directed toward pathogenic members of the genus treponema. For diagnostic purposes thereby, TPHA is used as the gold standard. In USA, nontreponemal tests such as RPR are recommended for screening and then confirmed with standard treponemal tests such as fluorescent treponemal antibody absorption test or TPHA.

High risk behaviors', sexually promiscuity, men having sex with men as well as having multiple sexual partners are the risk factors associated with an increased incidence of syphilis infection among the blood donors. Hence, screening for syphilis is a good marker for a high risk activity among the donor population.

Our experience with RPR testing re-emphases the high false positivity of the test and raises the question of retaining or cessation of syphilis donor screening by nontreponemal tests in our setting. Detection of HBV DNA also indicates the importance of screening of syphilis as a surrogate marker for the high risk behavior of a donor.

 
   References Top

1.
Egglestone SI, Turner AJ. Serological diagnosis of syphilis. PHLS Syphilis Serology Working Group. Commun Dis Public Health 2000;3:158-62.  Back to cited text no. 1
    
2.
Nandwani R, Evans DT. Are you sure it's syphilis? A review of false positive serology. Int J STD AIDS 1995;6:241-8.  Back to cited text no. 2
    
3.
Augenbraun MH, DeHovitz JA, Feldman J, Clarke L, Landesman S, Minkoff HM. Biological false-positive syphilis test results for women infected with human immunodeficiency virus. Clin Infect Dis 1994;19:1040-4.  Back to cited text no. 3
    
4.
Naidu NK, Bharucha ZS, Sonawane V, Ahmed I. Comparative study of Treponemal and non-Treponemal test for screening of blood donated at a blood center. Asian J Transfus Sci 2012;6:32-5.  Back to cited text no. 4
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Correspondence Address:
Satyam Arora
Blood Bank, Dr. Ram Manohar Lohia Hospital, New Delhi - 110 001
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0973-6247.150979

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2006 - Asian Journal of Transfusion Science | Published by Wolters Kluwer - Medknow
Online since 10th November, 2006