Recommendations for Screening, Testing, and Management of Blood Donors and Blood and Blood Components Based on Screening Tests for Syphilis: Guidance for Industry

Administrative guidance, not enacted legislation. This captured publisher edition preserves the listed document and attachments; later developments are not independently consolidated.

Recommendations for Screening,
Testing and Management of Blood
Donors and Blood and Blood
Components Based on Screening Tests
for Syphilis
Guidance for Industry
Additional copies of this guidance are available from the Office of Communication, Outreach
and Development (OCOD), 10903 New Hampshire Ave., Bldg. 71, Rm. 3128, Silver Spring,
MD 20993-0002, or by calling 1-800-835-4709 or 240-402-8010, or email ocod@fda.hhs.gov, or
from the Internet at https://www.fda.gov/vaccines-blood-biologics/guidance-compliance-
regulatory-information-biologics/biologics-guidances.
For questions on the content of this guidance, contact OCOD at the phone numbers or email
address listed above.
U.S. Department of Health and Human Services
Food and Drug Administration
Center for Biologics Evaluation and Research
September 2014
Updated December 2020

Contains Nonbinding Recommendations
Recommendations for Screening,
Testing and Management of Blood
Donors and Blood and Blood
Components Based on Screening Tests
for Syphilis
_________________________________________________
Guidance for Industry
Note: Changes have been made to update the guidance of the same title dated September 2014,
including:
• 	Revised the recommended deferral period following treatment for syphilis or gonorrhea
to 3 months;
• 	Added a recommendation for reentry of donors with false positive screening test results
who are subsequently determined to have never had a diagnosis of syphilis;
• 	Removed the recommendation for donors to provide written evidence of completion of
syphilis treatment prior to reentry;
• 	Updated Code of Federal Regulation citations to reflect current requirements; and
• 	Made editorial or formatting changes.

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Table of Contents
I. 	INTRODUCTION............................................................................................................. 1
II. 	BACKGROUND ............................................................................................................... 2
A. 	Transfusion-Transmission of Syphilis................................................................. 2
B. 	Testing of Blood and Blood Components for Syphilis ....................................... 3
III. 	CHARACTERISTICS OF SEROLOGIC ASSAYS FOR SYPHILIS ........................ 4
IV. 	RECOMMENDATIONS FOR DONOR TESTING AND MANAGEMENT AND
PRODUCT DISPOSITION WHEN USING TESTS FOR SYPHILIS........................ 5
A. 	Identification of Donors with a History of Syphilis ........................................... 5
B. 	Donor Testing and Management When Using a Nontreponemal Screening
Test as the Test of Record for the Detection of Syphilis (See Figure 1) ........... 6
C. 	Donor Testing and Management When Using a Treponemal Screening Test
as the Test of Record for the Detection of Syphilis (See Figure 2) ................... 9
V. 	REFERENCES ................................................................................................................ 12

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Recommendations for Screening, Testing and Management of Blood
Donors and Blood and Blood Components Based on Screening Tests
for Syphilis
Guidance for Industry
This guidance represents the current thinking of the Food and Drug Administration (FDA or
Agency) on this topic. It does not establish any rights for any person and is not binding on FDA
or the public. You can use an alternative approach if it satisfies the requirements of the
applicable statutes and regulations. To discuss an alternative approach, contact the FDA staff
responsible for this guidance as listed on the title page.
I. 	INTRODUCTION
We, FDA, are providing you, blood establishments that collect Whole Blood or blood
components, including Source Plasma, with recommendations for screening and testing of
donors and management of donations based on screening tests for syphilis. Syphilis is a relevant
transfusion-transmitted infection (Title 21 Code of Federal Regulations (CFR) 630.3 (h)(1)(v)).
Licensed blood establishments must report the implementation of the recommendations
contained in this guidance in accordance with 21 CFR 601.12.1
This guidance updates the guidance of the same title dated September 2014. The September
2014 guidance finalized the draft guidance of the same title dated March 2013, and superseded
the memorandum dated December 12, 1991, entitled “Clarification of FDA Recommendations
for Donor Deferral and Product Distribution Based on the Results of Syphilis Testing.”
In general, FDA’s guidance documents, including this guidance, do not establish legally
enforceable responsibilities. Instead, guidances describe FDA’s current thinking on a topic and
should be viewed only as recommendations, unless specific regulatory or statutory requirements
are cited. The use of the word should in FDA’s guidances means that something is suggested or
recommended, but not required.
1 Licensed blood establishments that implement the revised recommendations for donor deferral and reentry
provided in this updated guidance document, dated December 2020, must report the changes to FDA in an annual
report under 21 CFR 601.12(d), noting the date the process was implemented.

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II. 	BACKGROUND
A. 	Transfusion-Transmission of Syphilis
Syphilis, caused by the spirochete Treponema pallidum (T. pallidum), is most often
acquired after sexual contact with an infected individual. Syphilis can also be transmitted
from mother to child or, rarely, transmitted by transfusion of blood or blood components
from donors with active syphilis (Ref. 1). The last reported case of transfusion-
transmitted syphilis in the United States (U.S.) occurred in 1966 (Ref. 2). Universal
testing of blood donors may have played a role in the disappearance of transfusion-
transmitted syphilis. Other possible explanations for the decline in transfusion-
transmitted syphilis include: that direct donor-to-recipient transfusions no longer take
place; inactivation of T. pallidum (a cold-sensitive microorganism) in refrigerated blood
components; the decline in rates of syphilis in the general population, which in turn is
reflected in the donor population; self-deferral of blood donors who are ill during
spirochetemia (presence of spirochetes—the causative agent of syphilis infection—in the
circulating blood); screening and deferral of potential donors who report high risk
behavior for acquiring syphilis infection (e.g., persons who received money, drugs, or
other payment for sex); wide use of antibiotics among transfusion recipients; and
difficulties in diagnosing transfusion-transmitted syphilis in recipients (Ref. 3).
However, none of these explanations has been quantified or adequately validated.
Information from the American Red Cross on serological testing of donors revealed that
there were 324 cases of syphilis infections among American Red Cross repeat allogeneic
donors in 2007-2008, a figure several times higher than the numbers of repeat allogeneic
donors identified with human immunodeficiency virus (HIV), hepatitis B virus (HBV),
hepatitis C virus (HCV), and human T-cell lymphotropic virus (HTLV) infections, which
were 92, 47, 127 and 9, respectively, during the same time period (Ref. 4). Several
published studies (Refs. 5 through 9) that investigated the presence or absence of T.
pallidum nucleic acid in blood samples from individuals with confirmed or possible
syphilis detected spirochete nucleic acid in blood samples from persons with syphilis,
some of whom had a latent infection with no symptoms. Another study failed to confirm
that finding (Ref. 10). This suggests that some asymptomatic blood donors might have
spirochetemia. Donations from such blood donors might have the potential to transmit
syphilis to recipients. Although syphilis testing has a low sensitivity and positive
predictive value as a surrogate marker for detecting known transfusion-transmitted
viruses, in 2009, the American Red Cross published data (Ref. 11) indicating that there
were significantly higher rates of HIV-, HCV-, HBV-, HBsAg (hepatitis B surface
antigen)-, and HTLV-positive donations among donors with positive syphilis test results
compared to donors with negative syphilis test results.

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B. 	Testing of Blood and Blood Components for Syphilis
Current testing requirements for syphilis are found in 21 CFR 610.40(a)(2). Individuals
who test reactive 2 with a screening test for syphilis must be deferred (21 CFR 610.41(a))
and notified of their deferral (21 CFR 630.40). You must further test each donation
found to be reactive by a donor screening test, except you are not required to perform
further testing of a donation found to be reactive by a treponemal screening test for
syphilis (21 CFR 610.40 (e)). Additional testing to requalify the donor in accordance
with (21 CFR 610.41(b)) is recommended in sections IV.B and C of this document. In
accordance with (21 CFR 610.40(h)(2)(vi)), FDA allows use of blood and blood
components, excluding Source Plasma, that test reactive by a screening test for syphilis,
if the donation is further tested by an adequate and appropriate test which demonstrates
that the reactive screening test is a biological false-positive and the blood or blood
component is labeled with both test results. Under 21 CFR 610.40(h)(2)(vii), you may
use Source Plasma from a donor who tests reactive by a screening test for syphilis, if the
donor meets the requirements of 21 CFR 640.65(b)(2).
FDA requirements regarding syphilis testing specific to Source Plasma are as follows:
1. 	Current collection, testing and labeling requirements related to results of
serologic tests are found in 21 CFR 640.65 (b) and 606.121.
2. 	A sample of blood must be drawn from Source Plasma donors on the day of
the first medical examination or plasmapheresis, whichever comes first, and at
least every 4 months thereafter, and these samples must be tested for syphilis
(21 CFR 640.65(b)(1)(i)).
3. 	A donor with a reactive test result for syphilis must not be plasmapheresed
again until the donor tests nonreactive, except as stated in points 4 and 5,
below (21 CFR 640.65(b)(2)(ii)).
4. 	A donor with a reactive biologic false-positive syphilis test result may be
plasmapheresed, provided that the donor’s file: (a) identifies the reactive
serologic test and the results used to confirm the biologic false-positive
results; and (b) indicates that the physician on the premises has determined the
false-positive reaction is not the result of an underlying disorder that would
disqualify the donor from participating in the plasmapheresis program
(21 CFR 640.65(b)(2)(iii)).
5. 	A donor with a reactive syphilis test result may be plasmapheresed only to
obtain plasma to be used for further manufacturing into control serum for the
serologic test for syphilis, provided that: (a) the physician on the premises
2 The term “reactive” includes “repeatedly reactive” results. You should follow the instructions in the package
insert of the assay you are using.

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approves the donation; and (b) the donor’s file contains a signed statement
from a physician or clinic establishing that treatment for syphilis has
commenced and that continuance in the plasmapheresis program will not
interfere with or jeopardize the syphilitic donor’s treatment
(21 CFR 640.65(b)(2)(iv)).
6. 	Plasma collected from a donor with a reactive test result for syphilis must be
appropriately labeled, as stated in 21 CFR 606.121(e)(5)(iv).
III. 	CHARACTERISTICS OF SEROLOGIC ASSAYS FOR SYPHILIS
There are two different types of serologic assays for syphilis: (A) nontreponemal assays; and (B)
treponemal assays.
(A) Nontreponemal assays, such as the rapid plasma reagin (RPR) test, the venereal
disease research laboratory (VDRL) test, and the automated reagin test (ART), are non-
specific tests that detect “reagin” antibodies directed against an antigen called cardiolipin
that is present in a variety of tissues. Antibodies to cardiolipin appear in the serum of
persons with active syphilis or with other medical conditions. However, some
individuals who were previously infected with syphilis but successfully treated maintain
low levels of antibody to cardiolipin for a long time.
Sera and plasma from individuals previously infected with syphilis who were
successfully treated do not generally remain reactive in nontreponemal tests for more
than one to two years after successful treatment. Therefore, persons with active or
recently treated syphilis infections generally have reactive results with nontreponemal
tests, while uninfected persons or persons successfully treated years earlier usually have
nonreactive nontreponemal test results. Nontreponemal assays are useful in identifying
recent syphilis infection, and to monitor the progression of syphilis and response to
antibiotic therapy.
(B) Treponemal assays include enzyme immunoassays (EIA), fluorescent treponemal
antibody “absorbed” assays (FTA-ABS), Treponema pallidum microhemagglutination
assays (MHA-TPA) and Treponema pallidum particle agglutination assays (TP-PA).
Treponemal assays test for antibodies to antigens that are specific to treponemes.
Treponemal assays are most useful in identifying recent and past syphilis infections.
They are not generally useful in monitoring the response to antibiotic therapy. With
some exceptions, positive results of tests for specific treponemal antibodies remain
positive throughout an individual’s life regardless of whether the individual is currently
infected or has been cured following successful treatment (Ref. 12). Retesting sera that
are reactive in nontreponemal assays using a specific treponemal test is valuable in
distinguishing true-positive results that indicate active syphilis infection from biological
false-positive results due to other conditions.

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Since both the nontreponemal and treponemal assays detect antibodies rather than the infectious
treponemes themselves, neither assay reliably identifies patients in the “window period” of very
early syphilis, after infection has been acquired but before antibodies to either treponemal
antigens or to cardiolipin have appeared.
Many blood establishments use automated treponemal assays with high throughput that have
been cleared by FDA for purposes of screening donors for syphilis, such as the treponemal
assays EIA, MHA-TPA and TP-PA (Ref. 13). However, some blood establishments might be
using a nontreponemal assay as a screening test for syphilis. Therefore, we are providing
recommendations for management of donors and blood and blood components for situations in
which a blood establishment would use either a nontreponemal screening test or a treponemal
screening test.
To distinguish the results of screening tests for syphilis from the results of additional syphilis
tests, we use the terms “reactive” and “nonreactive” for results of screening tests (both
nontreponemal and treponemal) and reserve the terms “positive” and “negative” for results of
further testing using treponemal tests (used for donor counseling and requalification) on samples
of the same blood specimen previously used for screening. A test result that is read as
“indeterminate,” “questionable,” or equivocal” according to the package insert should be
considered as equivalent to a reactive test result (for screening tests) or positive test result (for
subsequent treponemal tests) for purposes of this guidance document.
Establishments that screen donors using a nontreponemal assay as the test of record may use a
treponemal diagnostic test for the purposes of further testing under 21 CFR 610.40(e), donor
reentry under 21 CFR 610.41(b), and also for demonstrating that a reactive screening test result
is a biological false-positive (21 CFR 610.40(h)(2)(vi)).
IV. 	RECOMMENDATIONS FOR DONOR TESTING AND MANAGEMENT AND
PRODUCT DISPOSITION WHEN USING TESTS FOR SYPHILIS
A. 	Identification of Donors with a History of Syphilis
1. 	To assess the eligibility of the donor as required in 21 CFR 630.10(e), we
recommend that you assess donors for a history of syphilis or gonorrhea or
treatment for syphilis or gonorrhea in the past 3 months.
2. 	We recommend that you defer for 3 months after completion of treatment, an
individual with a history of syphilis or gonorrhea or treatment for syphilis or
gonorrhea in the past 3 months. After this 3 -month period, the individual
may be eligible to donate provided the individual meets all donor eligibility
criteria.

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B. 	Donor Testing and Management When Using a Nontreponemal Screening
Test as the Test of Record for the Detection of Syphilis (See Figure 1)
You must test each donation of blood and blood components for syphilis using a
serological test (21 CFR 610.40 (a)(2)). You must test a donor of Source Plasma for
syphilis at least every 4 months (21 CFR 640.65(b)(1)(i)). You must use a serological
screening test for syphilis cleared by FDA for such use (21 CFR 640.10(b)).
1. 	If the nontreponemal screening test is nonreactive, the donor is considered to
be negative for syphilis infection. You may release the donation, provided it
meets all donation suitability requirements, and retain the donor.
2. 	If the nontreponemal screening test is reactive, you must defer the donor
indefinitely (21 CFR 610.41(a)), unless evaluated for reentry, following the
method described below. However, Source Plasma donors may be allowed to
donate plasma for further manufacture into noninjectable products (21 CFR
640.65(b)(2)(ii) through (iv)).
You must perform further testing as required in 21 CFR 640.10(e) to provide
additional information concerning the reactive donor’s infection status.
You must not ship or use the donation, unless an exception for shipment or
use is applicable (21 CFR 610.40(h)). As provided in 21 CFR 610.40
(h)(2)(vi) and (vii), you may use the donation when a negative treponemal test
result is obtained using the method described below.
Product Management and Reentry under 21 CFR 610.41(b) of Deferred Donors
3. 	If the nontreponemal test is reactive, you may perform a treponemal test 3
using either a sample from the index donation or a follow-up sample from the
donor collected at a later date.
a. 	If the treponemal test result is negative (suggesting that the reactive
nontreponemal test result is a biological false-positive result), you may
reenter the donor under 21 CFR 610.41(b).
If the sample tested was from the index donation, the donation, excluding
Source Plasma, may be released (21 CFR 610.40(h)(2)(vi)), provided the
donation meets all other suitability requirements, and must be
appropriately labeled under 21 CFR 610.40(h)(2)(vi) and 21 CFR 606.121.
Under 21 CFR 610.40(h)(2)(vii), you may use Source Plasma from a
3 Establishments may use a treponemal diagnostic test for further testing (21 CFR 610.40(e)), donor reentry (21
CFR 610.41(b)) or for demonstrating that the reactive screening test is a biological false-positive (21 CFR
610.40(h)(2)(vi)).

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donor who tests reactive by a screening test for syphilis, if the donor meets
the requirements of 21 CFR 640.65(b)(2)(ii)-(iv).
You may consider counseling the donor about the potential medical
significance of a biological false-positive screening test.
b. 	If the treponemal test result is positive, you must continue to defer the
donor indefinitely (21 CFR 610.41(a)) unless evaluated for reentry.
You must discard the donation unless an exception for shipment or use is
applicable (21 CFR 610.40(h)).
You may reenter the donor under 21 CFR 610.41(b) if the donor
subsequently reports being treated for syphilis, provided that the treatment
was successful and completed at least 3 months before the next donation;
and the donor meets all donor eligibility criteria.
Alternatively, the donor may be reentered without treatment if your
responsible physician determines that the donor never had syphilis based
on subsequent medical evaluation and diagnostic testing for syphilis (i.e.,
the screening results were falsely positive), and the donor meets all donor
eligibility criteria.
You may use either an FDA-cleared nontreponemal screening test or an
FDA-cleared treponemal screening test to test the reentered donor’s
subsequent donations.
The donor remains indefinitely deferred if the donor was not treated for
syphilis or was not medically evaluated for reentry.

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Figure 1: Donor Testing and Management When Using a Nontreponemal Screening Test as the
Test of Record for the Detection of Syphilis
1 The term “reactive” includes “repeatedly reactive” results. You should follow the instructions in the package insert
of the assay you are using.
2Source Plasma donations with these test results may be used under some circumstances, but the donor must be
deferred unless certain conditions apply (21 CFR 610.40(h)(2)(vii)) and 21 CFR 640.65(b)(2)(ii) through (iv)).
Other donations must not be used unless a negative treponemal test result is obtained or another exemption under
(21 CFR 610.40(h)(2)) applies.
3 You may use a treponemal diagnostic test for further testing (21 CFR 610.40(e)), donor reentry (21 CFR
610.41(b)) and for demonstrating that the reactive screening test is a biological false-positive (21 CFR
610.40(h)(2)(vi)).
4 Consider counseling the donor about the possible medical significance of a biological false-positive result.
5
Sample tested must be from the index donation. Excluding Source Plasma, you must label such donations as
reactive by a screening test for syphilis and negative by a treponemal test (21 CFR 610.40(h)(2)(vi)). Under 21
CFR 610.40(h)(2)(vii), you may use Source Plasma from a donor who tests reactive by a screening test for
syphilis, if the donor meets the requirements of 21 CFR 640.65(b)(2)(ii)-(iv).

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C. 	Donor Testing and Management When Using a Treponemal Screening Test
as the Test of Record for the Detection of Syphilis (See Figure 2)
You must test each donation of blood and blood components for syphilis using a
serological test (21 CFR 610.40(a)(2)). You must test a donor of Source Plasma for
syphilis at least every 4 months (21 CFR 640.65(b)(1)(i)). You must use a serological
screening test for syphilis cleared by FDA for such use (21 CFR 640.10(b)).
1. 	If the treponemal screening test is nonreactive, the donor is considered to be
negative for syphilis infection. You may release the donation, provided it
meets all donation suitability requirements, and retain the donor.
2. 	If the treponemal screening test is reactive, further testing is not required, and
you must defer the donor indefinitely (21 CFR 610.41(a)) unless evaluated for
reentry following the method described below. However, Source Plasma
donors may be allowed to donate plasma for manufacture into non-injectable
products (21 CFR 640.65(b)(2)(iv)).
In addition, you must not ship or use the donation, unless an exception for
shipment or use is applicable (21 CFR 610.40(h)).
Reentry under 21 CFR 610.41(b) of Deferred Donors
3. 	Because the possibility exists that a treponemal test might be false-positive for
reasons unrelated to the analyte (e.g., failure to remove excess conjugate
during the performance of the test), the donor may be eligible for reentry.
You may perform another treponemal screening test that is different from the
initial treponemal screening test used as the test of record, using either a
sample from the index donation or a follow-up sample from the donor
collected at a later date. 4
a. 	If the additional treponemal screening test result is negative, you may
reenter the donor.
b. 	If the additional treponemal screening test result is positive, the donor
remains deferred indefinitely (21 CFR 610.41(a)) unless evaluated for
reentry, as described below.
4 When treponemal screening test results are reactive, we do not consider negative results on an additional
treponemal test to be indicative of biological false-positives on the screening test under 21 CFR 610.40(h)(2)(vi).
Regardless of the result from the additional treponemal screening test, you must not release the index donation
unless an exception applies (21 CFR 610.40(h)). Source Plasma donations with these test results may be used under
some circumstances, provided that the requirements under 21 CFR 610.40(h)(2)(vii) and 21 CFR 640.65(b)(2)(ii)
through (iv) are met.

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For reentry purposes, you may test the sample from the donor which was
positive on the additional treponemal screening test using a nontreponemal
screening test to assess whether the donor has an active infection. 5 If the
nontreponemal screening test result is negative, the results are consistent
with recovery or cure from a previous syphilis infection. If the
nontreponemal screening test is positive, the results are consistent with an
active or recently treated syphilis infection.
In either case, you may reenter the donor under 21 CFR 610.41(b) if the
donor subsequently reports being treated for syphilis, provided the
treatment was successful and completed at least 3 months before the next
donation; and the donor meets all donor eligibility criteria.
Alternatively, the donor may be reentered if your responsible physician
determines that the donor never had syphilis based on subsequent medical
evaluation and diagnostic testing for syphilis (i.e., previous test results
were falsely positive), and the donor meets all donor eligibility criteria.
You may use either a nontreponemal screening test or a treponemal
screening test that has been cleared by FDA for such intended use to test
the reentered donor’s subsequent donations.
The donor remains indefinitely deferred if the donor was not treated for
syphilis or was not medically evaluated for reentry.
5 Further testing under 21 CFR 610.40(e) is not required; however, performing a nontreponemal test after positive
treponemal test results are obtained can assist in determining a donor’s status in regard to syphilis infection and in
determining eligibility of the donor.

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Figure 2: Donor Testing and Management When Using a Treponemal Screening Test as
the Test of Record for the Detection of Syphilis
1The term “reactive” includes “repeatedly reactive” results. You should follow the instructions in the package insert
of the assay you are using.
2 Source Plasma donations with reactive test results for syphilis may be used under some circumstances, but the
donor must be deferred, unless certain conditions apply (21 CFR 610.40(h)(2)(vii)) and 21 CFR 640.65(b)(2)(ii)
through (iv)). Other donations must not be used unless another exemption under 21 CFR 610.40(h)(2) applies.
3 Further testing is not required; however, performing a nontreponemal test after positive treponemal test results are
obtained can assist in determining a donor’s status in regard to syphilis infection and in determining future eligibility
of the donor.

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V. 	REFERENCES
1. 	Turner TB and Diseker TH. Duration of infectivity of Treponema pallidum in citrated
blood stored under conditions obtaining in blood banks. Bull Johns Hopkins Hosp 1941;
68:269-279.
2. 	Chambers, RW, Foley, HT, Schmidt, PJ. Transmission of syphilis by fresh blood
components. Transfusion 1969; 9:32-34.
3. 	Katz, LM. A test that won’t die: the serological test for syphilis. Transfusion 2009;
49:617-619.
4. 	Zou, S, Stramer, SL, Dodd, RY. Donor testing and Risk: current prevalence, incidence,
and residual risk of transfusion-transmitted agents in US allogeneic donations.
Transfusion Medicine Reviews 2012; 26(2):119-128.
5. 	Marfin, AA, et al. Amplification of DNA polymerase I gene of Treponema pallidum
from whole blood of persons with syphilis. Diagnostic Microbiology and Infectious
Disease 2001; 40:163-166.
6. 	Kouznetzov, AV, et al. Detection of the 47-kilodalton membrane immunogen gene of
Treponema pallidum in various tissue sources of patients with syphilis. Diagnostic
Microbiology and Infectious Disease 2005; 51:143-145.
7. 	Castro, R, et al. Detection of Treponema pallidum sp pallidum DNA in latent syphilis.
International Journal of STD & AIDS 2007; 18:842-845.
8. 	Flasarova, M, et al. (Abstract) Molecular detection and subtyping of Treponema
pallidum subsp. Pallidum in clinical specimens. Epidemiol. Mikrobiol. Immunol. 2006;
3:105-111.
9. 	Rodionova, EN, et al. Detection of Treponema pallidum DNA and RNA in clinical
material from patients with syphilis at different stages. Zh. Mikrobiol Epidemiol.
Immunobiol. 2003; 3:43-50.
10. 	Orton, SL, et al. Prevalence of Treponema pallidum DNA and RNA in blood donors
with confirmed-positive syphilis tests. Transfusion 2002; 42:94-99.
11. 	Zou, S, Notari, EP, Fang, CT, Stramer, SL, Dodd, RK. Current value of serologic test for
syphilis as a surrogate marker for blood-borne viral infections among blood donors in the
United States. Transfusion 2009; 49:655-661.
12. 	Centers for Disease Control and Prevention. Discordant results from reverse sequence
syphilis screening. MMWR 2011 (February); 60(5):133-137.
13. 	Aberle-Grasse J, Orton SL, Notari E IV, Layug LP, Cable RG, Badon S, Popovsky MA,
Grindon AJ, Lenes BA, Williams AE. Predictive value of past and current screening tests
for syphilis in blood donors: changing from a rapid plasma reagin test to an automated
specific treponemal test for screening. Transfusion 1999 (February); 39(2):206-211.