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568 The Immunoassay Handbook
sample directly from an automated track to the ADVIA
Centaur XP, making the system efﬁcient for managing
Assay protocols, which are stored in memory, utilize com-
petitive binding, immunometric (sandwich) principles, anti-
gen bridging, and µ-capture depending on the speciﬁc
assay. The system can perform one-step, extended one-
step, two-step, and extended two-step incubation protocols.
Quantiﬁcation of results is achieved by oxidation of the
acridinium ester (AE) tracer reagent, followed by detection
and quantiﬁcation of the resultant intense quick ﬂash emis-
sion. Assays are performed in discrete disposable cuvettes,
which may be loaded and replenished randomly at any time.
The AE-based chemiluminescence methodology fea-
tured in ADVIA Centaur XP has always been a state-of-
the-art methodology but is also a dynamic technology
undergoing continuing evolution and innovation. Ongo-
ing research has allowed continuing development of next-
generation assays that meet or exceed the evolving demand
for improved performance in various clinical applications.
Key to these adaptations is the fact that the AE technology
is based on a family of chemiluminescent structures that
can be selectively optimized for individual assays. These
ongoing modiﬁcations provide opportunities for improved
detection and precision.
An example of an immunometric ADVIA Centaur XP
assay principle is shown in Fig. 3.
AE Enhancement Features
G High quantum yield. High signal-to-noise ratio
enhances sensitivity and low-end precision.
G Hydrophilicity. Improves efﬁcacy of the wash step,
yielding low nonspeciﬁc binding.
G Hydrolytic stability. Yields long reagent shelf life and
extended onboard stability.
G Versatility. Suitable for labeling small haptens, large
antigens, antibodies—supporting an extensive assay
G Small size. Analytes directly labeled with AE differ
minimally from native analyte.
G Simplicity. Uncomplicated mechanism for light trig-
gering with hydrogen peroxide and base.
G Rapid kinetics. Light emission complete in 1–5s, allow-
ing high throughput.
ADVIA Centaur XP assays are calibrated using a stored,
lot-speciﬁc, or ﬁxed master curve of up to 10 concentra-
tion points, depending on the assay. The curves are
1 Primary reagent compartment 12 Ancillary probe
2 Primary reagent probes 13 Sample probe
3 Incubation ring 14 Ancillary reagent queue
4 Luminometer 15 Sample tip tray
5 Base probe 16 Inprocess queue
6 Waste probe 17 Sample entry queue
7 Cuvette loading bin 18 Sample rack
8 Aspirate probes 19 Stat entry
9 Magnets 20 Sample exit queue
10 Wash block 21 User Interface workstation
11 Acid probe
FIGURE 2 ADVIA Centaur XP system—top view (The color version of this ﬁgure may be viewed at www.immunoassayhandbook.com).
569CHAPTER 7.10 ADVIA Centaur® XP
established by the Quality Control Laboratory at Siemens
Healthcare Diagnostics. These master curves are supplied
on a bar-coded card for rapid and accurate entry into the
memory of the ADVIA Centaur XP user interface. The
master curve is then used by the software to quantify each
assay performed with that lot of reagents. Calibration eval-
uation ranges, which include slope, ratio, low, and high
calibrator deviation and precision, ensure a valid calibra-
tion. Periodic recalibration is accomplished by inclusion of
a set of two calibrators. Recalibration intervals vary
depending on the assay and are tracked and controlled by
onboard software. Multiple master curves may be stored in
system memory for each assay, simplifying lot to lot
switching. Raw data (relative light units) for control and
patient data are retained by the system when a valid cali-
bration is not present for the speciﬁed assay and can be
quantiﬁed as soon as the calibration is valid.
A combination of polyclonal and mouse monoclonal anti-
bodies is used in many ADVIA Centaur assays. In immu-
nometric assays, this multispecies technology minimizes
the risk of aberrant results due to heterophilic binding by
human anti-mouse antibodies (HAMA), which can occur
in dual mouse monoclonal assays. Where dual mouse
monoclonal antibodies are utilized, blocking reagents are
added to minimize the risk of HAMA effects.
The solid-phase reagents used in the ADVIA Centaur
assays are suspensions of micron sized, specially coated fer-
ric oxide particles. These particles are small enough to pro-
vide extremely high surface area for rapid binding kinetics
and stay in suspension for prolonged periods but are rapidly
and cleanly separated through their paramagnetic attrac-
tion when placed in a magnetic ﬁeld. The ADVIA Centaur
refrigerated reagent compartment gently rocks the reagent
packs at periodic intervals. The reagents are packaged in a
Ready-Pack® that contains an S-shaped ﬂow design for
optimal resuspension of the particles. The Paraﬁlm®-like
coating covers the pack openings that are punctured during
reagent probe aspiration. Individual assay packs provide
sufﬁcient volume for 50–200 tests (see Fig. 4).
After dispensing the sample, tracer and solid-phase
reagents into the test cuvette, and completion of the incuba-
tion period, the particles are magnetically pulled to the ﬂat
wall of the cuvette by magnets mounted on the back of a ring
within the incubation chamber. This separate ring allows the
FIGURE 3 Example of ADVIA Centaur XP assay principle (immunometric type).
570 The Immunoassay Handbook
magnets to move within the ring to any location that they are
required. The liquid contents of the cuvette are aspirated,
then water or a specially formulated wash solution is injected
to resuspend and remove the nonspeciﬁc bound tracer. Rese-
paration is accomplished automatically in this step.
Water is provided from an onboard reservoir (1.5L
capacity) fed by a connection to a deionized water supply.
A bulk water bottle (9.5L capacity) is available for labs that
cannot provide a direct connection. The liquid waste is let
away from the system to a laboratory disposal area. A bulk
waste container, into which the waste may be emptied
while the system is running, is also available for labs that
do not have the infrastructure to support direct waste dis-
charge. When the system is directly plumbed to water and
waste, no operator intervention is required.
Following separation and washing of the solid-phase par-
ticles, they are resuspended in an oxidizing reagent at an
acid pH, stored onboard (acid reagent). While held in
front of a photomultiplier tube detector, a pH adjusting
reagent, also stored onboard (base reagent) is injected,
causing the dose-related light emission which is quantiﬁed
over a period of 4s. The acid and base reagents have a bulk
bottle and reservoir stored onboard, so that the reagents
may be replenished at any time during a run.
The ﬂash emission, corrected by background subtraction, is
directly related to the stored master curve for quantiﬁcation.
Results are calculated and reported as mass concentration
and ﬂagged if out of range, based upon operator-controlled
reporting formats. The software allows automatic conver-
sion to SI units, if desired. Results may be reported individu-
ally as completed or collated into patient reports containing
all tests performed on a given sample.
If desired, the ADVIA Centaur will automatically hold a
sample in the in-process queue for repeat, if the initial
result is outside an operator-programmed range.
An unlimited number of controls can be deﬁned for
each analyte and may be tracked through a 90 day history,
and results are displayed in a tabular or Levey-Jennings
format. QC rules can be set to evaluate system perfor-
mance. Monthly summaries are also accessible for a period
of 12 months. Results from 25,000 tests are stored in a cur-
rent or historical worklist view.
The user interface of the ADVIA Centaur XP is a
19 inch high-resolution LCD touch screen. The use of
intuitive icons and full online help throughout the soft-
ware makes training and routine operation rapid and
simple to master.
A built-in high-speed CD-ROM reader allows easy
loading of software and test deﬁnitions. Step-by-step
instructions and graphics for activities such as mainte-
nance, system diagnostics, and troubleshooting are
available through the help and online procedures in the
A remote access feature has been built into the ADVIA
Centaur XP to allow Siemens Technical Assistance groups
access to pertinent system information via the internet to
aid in troubleshooting and provide rapid problem
Interfacing to Laboratory
Bidirectional interfacing to any central laboratory com-
puter is achievable for downloading of testing requests,
host query options, and uploading of test results, using
bar-coded samples. Interfacing software is written in stan-
dardized ASTM format for consistency with a wide variety
of LIS systems. Additionally, simple software selections
may be made to allow direct sampling from the back of the
system off an automated track. Operators can still load
routine and STAT samples manually at the front of the
system without interfering with the track. This ﬂexibility
allows the Centaur to easily integrate into totally auto-
mated laboratory systems.
Day, R., Horschke, W., Hallahan, M., Jackson, T. and Williams, J. System
design solutions for high volume immunoassay analysis. J. Clin. Ligand Assay
22, 184 (1999).
Geyer, S., Moore, S. and Michetti, D. A study of the potential impact of the ACS:
Centaur in a hospital core laboratory. Clin. Chem. 44, A57 (1998).
Girgensohn, S., Liedtke, R., Balzer, G., Castor, S. and Hauser, M. Performance
of the ACS:Centaur high-capacity, random-access immunoassay system.
Clin. Lab. 43, 975–983 (1997).
Weinzierl, C. Productivity evaluation of random-access immunoassay platforms.
Am. Clin. Lab. 16, 4–5 (1997).
FIGURE 4 The Ready-Pack®, containing the test reagents (The color
version of this ﬁgure may be viewed at www.immunoassayhandbook.com).