Screening for cancer: are biomarkers of value?

– February/March 2011 30 Microbiology
specificity compared with the FTA-ABS and
TPPA [6]. In addition they can be automated,
facilitating the objective reading of results. The
reader can be linked to the laboratory computer,
which reduces the variation and subjectivity
of manual reading. However, EIAs based
on treponemal antigens, like other treponemal
tests, give positive results throughout life even
after successful completion of therapy. The
sensitivity of EIA is also no greater than the
TPHA for primary syphilis. The CDC recommends
that if the EIA is used for screening, an
RPR test should be performed on all positive
samples, and a second treponemal test, such as
TPPA or FTA-ABS, should be used to confirm
a positive result.
Fluorescent Treponemal Antibody
Absorption Test (FTA-Abs)
This indirect fluorescent antibody test utilises
fluorescent dye to detect antibodies against
treponemal antigens. Serum or plasma is
pretreated with absorbent to remove groupspecific
treponemal antibodies. The FTA
- Abs double staining test is a modified FTA-
Abs which uses an additional counter stain
to improve the reliability of the results. Even
though it is highly sensitive, especially in early
primary syphilis, it is less sensitive than other
treponemal tests for detecting markers of
past infection [2]. The specificity of FTA-Abs
is also lower than in other treponemal tests.
False positives occur in approximately 1-2%
of the normal population, mainly in patients
with immune haemolytic anaemia, some viral
infections and in narcotic addicts [2]. Furthermore
an effective, specialised and qualitycontrolled
microscope is required for the test.
Immunoblotting
This technique detects antibodies to individual
T. pallidum proteins. Antibodies reacting to
some of the treponemal antigens such as 15
kDa, 17 kDa, 44.5 kDa and 47 kDa are diagnostic
for acquired syphilis [2]. Either IgG or IgM
antibodies are detected, which is useful for a
confirmatory test [4, 6]. Recently recombinant
antigens, in place of electrophoretically fractionated
proteins, have improved the test, but it
cannot be performed in a small scale laboratory;
the test is only available in selected laboratories.
Rapid tests
Rapid tests using treponemal antigen(s)
coated on latex particles and nitrocellulose
(ICT) strips are available for testing blood,
serum or plasma. Such simple, rapid tests
are more useful in the field, in resource-poor
settings and in the physician’s office, as technical
expertise and specialised instruments
are not required. However rapid tests do not
incorporate an internal Quality Control, so
a periodic external Quality Control using
laboratory-based tests is recommended [6].
One such test is Span Diagnostics’s Signal –Tp
ver. 2.0, an Immunodot test utilising a mixture
of purified recombinant, treponemal antigens
(47 kDa, 17 kDa), which are among the
major immunoreactive antigens in Western
Blot analysis and have shown great promise
in the development of a rapid diagnostic test
for syphilis [3,4]. Another test, Span Diagnostics’s
Crystal- Tp, is based on an immunochromatographic
technique which detects all
major classes of antibodies i.e. IgG, IgM, IgA
to treponemal antigens. A mixture of purified
recombinant antigens is used- 15 kDa, 47 kDa
and 17 kDa- which are major immunoreactive
antigens in the Western Blot technique [3,4].
These two tests have an inbuilt control dot/
line. They are 100% sensitive when compared
with a confirmed positive serum sample panel
for anti treponemal antibodies, and 100% specific
when compared with the TPHA.
Practical utility of serological tests
In the laboratory diagnosis of syphilis, it is most
important to detect the antibody response
with a screening test and confirm positive
results using a confirmatory test. An ideal
screening test should be simple, readily available,
cost-effective, rapid, user-friendly, suitable
for resource-poor situations and easily
adapted for use with a large number of specimens.
Sensitivity should be high, whereas the
confirmatory test should have both high sensitivity
and specificity, even at the cost of ease,
economy and simplicity, to rule out all false
positives without missing any positive samples.
Although this combination provides an
excellent screen for all stages of syphilis except
for very early primary infections, when the
treponemal test will not be positive, the cost
should be considered. In collaboration with
CDC, Span Diagnostics has developed world’s
first dual-test in a flow-through format, the
Signal Spirolipin, which detects reagin (i.e.
nonspecific) as well as anti treponemal (i.e.
specific) antibodies against a mixture of 47
kDa and 17 kDa antigens in a single test. This
can be used for screening and confirmation
of syphilis in almost all disease stages without
any prozone effect or false positives, and
can also be used to monitor treatment with
high specificity and sensitivity. Promising test
results have been found in neuro-syphilis,
congenital syphilis and in cases of syphilis/
HIV coinfection. This test makes diagnosis
quicker, more reliable, easier and more economical,
without the need for specialised
instruments and expertise. It is thus suitable
for field and epidemiological studies. The Signal
Spirolipin is a visual three dot assay with
an inbuilt control dot to validate successful
completion of the assay procedure; results are
available in 10 minutes.
References
1. CDC fact sheet, syphilis, 2008.
2. Nesteroff S. Serology, syphilis, RCPA Quality Programs Pty
Limited, 2004.
3. Egglestone SI and Turner AJL. Serological diagnosis of syphilis.
Communicable disease and public health 2000; 3:158-62.
4. Larsen SA, Steiner BM and Rudolph AH. Laboratory diagnosis
and interpretation of tests for syphilis. Clinical Microbiology
Reviews 1995; 8: 1-25.
5. Muller I, Brade V et al. Is serological testing a reliable tool in
laboratory diagnosis of syphilis? Meta-analysis of eight external
Quality control surveys performed by German Infection
Serology Proficiency testing program, Journal of Clinical
Microbiology 2006; 44:1335-1341.
6. Ratnam S. The Laboratory diagnosis of syphilis. The Canadian
Journal of Infectious disease and medical Microbiology 2005;
16:45-51.
7. Pope V et al. Comparison of serodia Treponema plallidum
particle agglutination Captia Syphilis-G and SpiroTek regain
II test with standard test technique for diagnosis of syphilis,
Journal of Clinical Microbiology, 2001;38:2543-2548.
The author
Dr M. Patel
SPAN DIAGNOSTICS LTD.
Udhna, Surat,
INDIA
www.cli-online.com & search 25516
Nova Biomedical increases
manufacturing capability
Nova Biomedical announced recently that, in
response to rapid growth in its diabetes and
whole blood point-of-care testing products
business, it has purchased an additional 7,500
square metres of manufacturing/warehouse
facility in Billerica, MA, USA. According to
Lou Borrelli, Nova Biomedical’s CFO, this
additional state of the art manufacturing facility
will ensure that the company’s manufacturing
capabilities keep pace with the increasing
demand for its StatStrip Hospital Glucose
products as well as its Nova Max consumer
diabetes products.
One of the main drivers for Nova’s strong
growth is the rapid adoption of its StatStrip
Hospital Glucose Monitoring System. Since
its inception just four years ago, StatStrip has
become the fastest growing hospital glucose
meter in the world. StatStrip uses a novel glucose
test strip technology that measures haematocrit
and other common interferences such
as maltose, galactose, xylose, acetaminophen,
ascorbic acid and oxygen, and eliminates erroneous
glucose results caused by these interfering
substances. StatStrip lab-like accuracy and
freedom from interference has been validated
in more than 50 published clinical studies
worldwide, in a broad variety of critical care
settings including ICU, Dialysis, NICU, OR,
ED, and Tertiary Care. This remarkable rate of
StatStrip publications by some of the world’s
leading hospitals, is testimony to the importance
of this technology breakthrough for bedside
glucose testing and suggests the reason for
its popularity.