Download the entire issue - American Association for Clinical ...

AACC’S ExPERT ACCESS
The Delta Check in Action
Causes and Consequences of Discrepant Laboratory Results
Each month, AACC’s Expert Access Live Online Program features a
different topic of importance to clinical laboratory practice.
Visit AACC’s website, www.aacc.org/events/expert_access, for more
information and an archive of past presentations.
the following is an excerpt from the March 2011
presentation by Joely straseski, phd, Mt(asCp),
dabCC, medical director of endocrinology at arup
laboratories in salt lake City, utah, and assistant
professor of pathology at the university of utah
school of Medicine.
Should results identified by delta
checking be flagged in the laboratory
information system? What comments
do you recommend?
When first identified, delta check flags
should indicate to the technologist that this
result exceeds the established delta limits
for this analyte and should be investigated,
for example, by repeating the test or calling
the clinician. This keeps the result from
being autoverified. Beyond that, if an investigation
reveals a sample integrity error,
results should be cancelled with a comment
describing the error, such as IV dilution
or EDTA contamination. It may be
helpful to document these types of issues,
since trends in sampling errors may be revealed
this way. If an investigation reveals
a misidentified specimen, results should be
cancelled with a comment describing that
issue as well. If a provider is contacted during
an investigation to confirm whether
the discrepant results are expected, and the
results fit with the clinical picture of the
patient, you might add a comment stating
that the clinician was contacted and results
were discussed. Then, upon review of the
patient chart, explanations for any large
fluctuations would be documented. A simple
comment such as “results repeated and
verified” is commonly added to repeated
18 CliniCal laboratory news July 2011
specimens and may be used for delta check
failures as well. If a result is “questionable,”
an investigation should be conducted to
clarify any issues before reporting.
Do delta checks alert only medically
significant discrepancies?
While labs traditionally use delta checks to
highlight medically important analyte concentrations,
they can be tailored to whatever
your needs may be. You can set up alert
limits specifically for your patient population
to highlight only likely misidentified
specimens, typically a large delta value, or
to highlight medically relevant changes in
analyte concentrations.
What is your perspective on delta checks
as it relates to autoverification?
Delta checks can certainly become part of
autoverification procedures. They are simply
another step in the autoverification process,
one that provides yet another layer of
confidence in your results before you send
them to the provider. The delta limits, once
determined, become additional rules that a
sample must follow in order to be autoverified.
For example, a rule involving sodium
levels would state: Is the sodium for this
patient less than 13 mEq/L different from
their sodium results over the past 3 days?
STAT Facts
atlanta, Georgia
Site of the 2011 AACC Annual Meeting
and Clinical Lab Expo
® population: 486,411
® City-owned parks: 277
® Churches: 1,500
® fortune 500 Companies: 13
® Zagat-rated restaurants: 700
® professional sports teams: 6
Sources: U.S. Census Bureau and Atlanta.net
If so, and if all other autoverification rules
have passed, autoverify the results. If not,
flag for further review or repeated analysis.
Do you recommend delta checks for
enzymes or other disease markers like
carcinoembryonic antigen (CEA)?
Yes, several institutions follow tumor
markers such as CEA. Delta checks for
these markers can be helpful, but you may
see fluctuations as patients go through
treatment, remission, etc. Although these
deltas will trigger a discrepant results investigation,
tumor markers are a valuable
analyte for delta checks. Alerting a clinician
to a large change in a tumor marker value
may be extremely important in the care
and management of that particular patient.
With the reliability of automated instruments,
is it truly necessary to repeat a
delta check?
This will vary depending on the analyte
and the methodologies and/or analyzers in
question. Review of quality control values
and a historical review of repeated values
within your institution may give you a better
indication of the analytical performance
of each specific analyte. This will help you
determine whether repeating delta check
failures is necessary.
I need help with percent difference
for delta checks between hematology
parameters.
Hematology was one of the first areas to
use delta checks, so there are several parameters
that may be helpful for you. Most notably,
the mean corpuscular value (MCV)
is a commonly used delta check, as this is
a value that should not change appreciably
within an individual. An examples of delta
check limits for MCV include: 4 fL over 2
days; 5 fL over any period of time; and 10 fL
over one day. Mean corpuscular hemoglobin
concentration (MCHC) is another
parameter with little biological variation
in the short term. Calculating the Index
of Individuality (II) for hematology tests
will help you identify good delta check
candidates. Beyond MCV and MCHC,
other hematology tests with low II include
hemoglobin, hematocrit, and platelet volume.
However, care should be used when
setting up delta checks on these measures,
since they can vary depending on the patient
population, for instance, in acute care
patients with hemorrhage.
How do you handle results that look
as though the sample might have been
contaminated with IV fluid?
The biological ramifications of reporting
results that have been diluted cannot be
stressed strongly enough. Each institution
may have their own procedure for dealing
with these types of specimens, and each
case is different. Although only one analyte
may be in question, such as absurdly elevated
glucose level possibly coming from the
IV, the chance that other analytes have been
similarly diluted is high. The safest course
of action is to redraw the patient; however,
that isn’t always possible. In the case where
only one analyte appears to be diluted, but
others were also ordered from the same
specimen, do a careful investigation of the
other analytes if there are recent results for
comparison. If any analytes are reported, a
comment regarding the possible dilution
with IV fluid should accompany the results.
Clinicians also should be alerted to interpret
results with caution. Generally speaking,
institutions’ policies vary as to the best
way to handle these types of situations.
How many days back should we include
in our delta checks?
Every analyte will be different. As you can
imagine, a difference in sodium may be
checked over a period of a few days, while
an ABO blood type could be stable over a
lifetime. An exaggerated example, but you
see the difference. Shorter timeframes are
usually more specific; as time goes on, differences
in an analyte may be attributed to
normal changes and not an acute process
or sampling issue.
Sampson and colleagues used time intervals
to optimize error detection with
delta checks (Sampson et al. Journal of
Clinical Ligand Assay 30:44–54, 2007).
They looked at 20 different analytes and
found that the optimal delta time interval
was generally between 2 and 5 days. Again,
this is extremely analyte-specific, and this
time interval is simply a general guide. Using
rate changes is another way to evaluate
delta values over time. However, the most
common way to determine the number of
days to use for delta check limits is experience
over time. Adjusting time limits will
allow you to balance lab staff investigations
and error detection. CLN
Disclaimer—The opinions and information
are the sole responsibility of the presenter.
AACC reviews the presentation for overall
appropriateness, but this should not be construed
as an endorsement by the association
or its employees of the opinions and information
offered here.
visit aacc.org
for professional
development,
meeting
registrations,
books,
and more.