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1 Add date in slide master | © 2017 Roche
CarOvr
Russell Sargon, Product Specialist
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eModule Carryover
• “CarOvr” flag is triggered when there is an extreme signal difference between two consecutive
measurements.
• The warning is an indication that a "potential micro particle carry over" within the analytical unit
may have occurred.
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eModule Carryover
• How can this be?
• Each sample on e411, e601, e602, e801 have unique tips and cuvettes (cups).
• But… they all end up going to one of the two measuring cells
(single measuring cell on e411).
• Measuring Cells are effectively flow cells with each sample cocktail entering sequentially with
a wash sequence between them.
• Within the 42 second cycle time of a measuring cell*, more than 40 seconds of that is dedicated to
measuring cell scrubbing, cleaning and preparation for the next sample.
• Theoretically however, if some of the material from one sample was not cleaned out
properly, it could remain in the measuring cell and affect the next sample reading.
*e801 is 24 seconds
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eModule Carryover
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eModule Carryover
• Light generated (RLU) by the ECL reaction is common to all analytes being measured
• Microparticles common to all Elecsys assays
Biotin
Ruthenium
Microparticle
Antigen
1O Antibody
2O Antibody
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eModule Carryover
• The alarm is generated if a sample with a very low RLU count happens to follow a sample through
the measuring cell with a very high RLU count:
• A low result sandwich assay follows a high result sandwich assay or a low result competitive
assay
• A high result competitive assay follows a high result sandwich assay or a low result
competitive assay
• if there was any sort of carryover, these are the samples that would be at risk.
• Hence the suggestion is to re-run that sample.
• In reality, no feedback about anyone re-running such a sample and getting a different result but it
is theoretically a risk.
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eModule Carryover
42 16812684 Time (seconds)
RLU
(620 n
m)
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eModule Carryover
42s 168s126s84s time
RLU
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eModule Carryover
• “It is technically impossible to measure the micro particle carry over in a single determination of a
sample.”
• Potential micro particle carry over is calculated by a mathematical algorithm.
• Equation is confidential but it takes to account different parameters like:
• actual measured low signals in counts,
• signals of previous measurement,
• assay specific factors that are encoded in the reference data,
• CutOff Signals for qualitative assays etc.
• Carry over calculation is not required between the last sample in a rack (eg rack 1, position 5) and
first sample in the next rack (eg rack 2 position 1)
• Because an additional washing step is carried out between both pipettings.
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eModule Carryover
• If seen often, it will be because of the order the tests going through a measuring cell.
• Orders tests are run depends on*:
• Host Order
• If a host is involved the e601 tests are pipetted in the same order as they are requested
by the host.
• If there is no host request but a profile run instead the pipetting order is the same as in the
list of the profile.
• If there is neither a host request nor a profile, then the pipetting order will be according to
the order of the Test Key setting from left to right.
* With exceptions
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eModule Carryover
• How to minimise the occurrence of CarOvr Flags?
• look at what tests are on each measuring cell and look to swap certain assays between the cells
to break up the measuring order.
• Try switching the positions of assigned QC positions - that is, first the high control, then the low
control
• Pipetting order can be influenced the by programming new Special Washes in case of many
CarOvr alarms!
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