Calling critical values to dialysis
Q What is your
position on calling chronic critical values? A BUN of 120 mg/dL on a
dialysis may not be considered “critical.” Currently, our lab calls
all critical values, multiple times, for the same patients, the same
result. Nurses opine that the result is not critical as the patient is
“known” to have an elevated test result. Consequently, with read-back
policy, nurses call the result to the physician who may feel the call is
unnecessary based on patient's history (e.g., end-stage renal disease,
or ESRD)
A This has been the
subject of questions, two articles, and letters in CAP Today.1,2,3,4,5
Several readers expressed similar views, that there should be a uniform
critical-value policy which should be followed in all cases. Reasons for
supporting this view are: a uniform lab policy is more likely to be
followed; and it is less confusing for the lab.
Stephen Sarewitz, MD, chair of the CAP Checklists
Committee, replied to one of the letters: “CLIA '88 states: 'The
laboratory must immediately alert the individual or entity requesting
the test and, if applicable, the individual responsible for using the
test results when any test result indicates an imminently
life-threatening condition, or panic or alert values.'
“Whether a particular lab result indicates an
imminently life-threatening condition depends, under certain limited
circumstances, on the clinical situation. For example, a low hematocrit
value may not be in a hemodialysis patient, yet it could be in a patient
from the general population. This distinction has nothing to do with
anyone's convenience; it is drawn cooperatively by the lab and
clinicians, as a way to identify which lab values are truly critical.
“The above practice is different from the
situation in which a clinician just does not want to be bothered by a
telephone call for a critical value.”2 I agree with Dr.
Sarewitz' comment.
In summary, 1) critical values should be set
jointly between clinicians and the lab; 2) exceptions to calling based
on clinical conditions may be defined, but this should be done as part
of the joint process, and it should be part of a well defined policy; 3)
physician-specific critical values should not be permitted; and
exception for the convenience of a physician or nurses should not be
permitted.
—Daniel M. Baer, MD
References
1. Yeransian N, Q and A, CAP Today.
Published May 2006.
http://www.cap.org/apps/cap.portal?_nfpb=true&cntvwrPtlt_actionOverride=%2Fportlets%2FcontentViewer%2Fshow&_windowLabel=cntvwrPtlt&cntvwrPtlt%7BactionForm.contentReference%7D=cap_today%2Fq_and_a%2F0506qa.html&_state=maximized&_pageLabel=cntvwr.
Accessed June 21, 2008.
2. Critical Values. Letter and reply. CAP
Today. Published August 2006.
http://www.cap.org/apps/cap.portal?_nfpb=true&cntvwrPtlt_actionOverride=%2Fportlets%2FcontentViewer%2Fshow&_windowLabel=cntvwrPtlt&cntvwrPtlt%7BactionForm.contentReference%7D=cap_today%2Ffeature_stories%2F0806letters.html&_state=maximized&_pageLabel=cntvwr.
Accessed June 21, 2008.
3. Paxton A. Critical thinking on critical
values.
CAP Today. September 2006.
http://www.cap.org/apps/cap.portal?_nfpb=true&cntvwrPtlt_actionOverride=%2Fportlets%2FcontentViewer%2Fshow&_windowLabel=cntvwrPtlt&cntvwrPtlt%7BactionForm.contentReference%7D=cap_today%2Fcover_stories%2F0906Critical_Values.html&_state=maximized&_pageLabel=cntvwr
Accessed June 21, 2008.
4. Critical Values. Letter. CAP Today.
Published October 2006.
http://www.cap.org/apps/cap.portal?_nfpb=true&cntvwrPtlt_actionOverride=%2Fportlets%2FcontentViewer%2Fshow&_windowLabel=cntvwrPtlt&cntvwrPtlt%7BactionForm.contentReference%7D=cap_today%2Ffeature_stories%2F1006Letters.html&_state=maximized&_pageLabel=cntvwr
Accessed June 21, 2008.
5. Making the right calls on critical values,
tests.
CAP Today. Published August 2008.
http://www.cap.org/apps/cap.portal?_nfpb=true&cntvwrPtlt_actionOverride=%2Fportlets%2FcontentViewer%2Fshow&_windowLabel=cntvwrPtlt&cntvwrPtlt%7BactionForm.contentReference%7D=cap_today%2F0808%2F0808_critical_values_4.html&_state=maximized&_pageLabel=cntvwr.
Accessed June 21, 2008.
Sed-rate control
Q We use
commercial sedimentation-rate controls. Frequently, we run out and are
told to use a random patient instead. I disagree; this substitution does
not prove a thing. The result is just a number in a book with no range
as a guideline. I was told that CLIA and the CAP recognize this. Can you
assist?
A Manual erythrocyte
sedimentation rates, or ESRs, are classified as waived tests under CLIA
'88; there are no federal regulatory specifications for quality control
of this test. Some semiautomated and automated methods for ESR, however,
have been classified as moderately complex under CLIA '88, which,
therefore, require two-level QC in 24 hours.
There are no specifically required QC materials
for ESRs in the CAP Laboratory Accreditation Program Hematology
Checklist. In the Laboratory General Checklist, however, there is a
question: “If the laboratory performs test procedures for which
calibration and control materials are not available, have procedures
been established to verify the reliability of patient test results?”1
This requires that the lab has written procedures to document the method
that the lab used for QC. From a CAP-accreditation perspective, the
essential elements are that all QC programs are technically and
scientifically valid and that appropriate actions are taken in response
to QC data. A CLSI guideline recommends the verification of the working
routine method against the reference method at a frequency determined by
the lab standard operating procedure.2
Many labs currently use commercial materials for
ESR QC, which provide adequate two-level controls. If commercial QC
materials are not available temporarily, the lab may use previously
tested patient samples (which need to be tested during validated QC
period by commercial QC materials) as current QC materials. Since the
previously tested results were validated by the QC procedure, the lab
can compare repeated (current) ESR test results with previously reported
results. If patient-sample results are repeatable, there is no problem
with the procedure. Of course, the lab needs to choose samples that
still are fresh (four to 24 hours after collection, depending on the lab
storage method and equipment requirement).
For the labs that do not use commercial QC
materials, lab directors need to define how ESRs will be controlled and
what the reference range is. This can be accomplished in a variety of
ways. For example, participate in extramural proficiency testing and
collect lab QC data from routine patient samples by calculating the
daily cumulative mean and monitoring its reproducibility over time.3
I agree that a couple of random patient samples is not appropriate QC
material.
— Guang Fan, MD, PhD
Medical
Director, Hematology Service
Department of Pathology
Oregon
Health and Science University
Portland, OR
References
1. CAP Laboratory Accreditation Program
Hematology and Laboratory General Checklist , GEN.30070, revised
9/27/2007.
2. Clinical and Laboratory Standards
Institute. Reference and Selected Procedure for the Erythrocyte
Sedimentation Rate (ESR) Test; Approved Standard — Fourth Edition.
Wayne, PA: Clinical and Laboratory Standards Institute; CLSI
Standard Document H02-A4.
3. Plebani M, Piva E. Erythrocyte
sedimentation rate: Use of Fresh Blood for Quality Control. Am J
Clin Pathol. 2002;117:621-626.
Urine sediment dilution
Q In our lab, the
hematology/urinalysis supervisor has been telling technologists to
dilute any thick sediment of urine with saline and multiply the result
by the factor. I have not followed this because I am afraid, among other
things, of missing significant casts. What I do instead is make a thin
prep on a regular slide, cover slip, and read. I have not read any
textbook prompting technologists to dilute urine sediment with saline. I
also have not encountered any hospital lab doing this. What would be the
effect of using saline as a diluent? If dilution is really necessary,
what diluent should be used? Please let me know if this practice
(dilution) is okay.
A This technique of
diluting blood and urine samples with saline solution is not an unusual
practice in most hematology and urine-cytology laboratories. If there is
a thick buffy coat or a large urine-sediment button, these procedures
may be necessary to allow for better distribution and interpretation of
the sample. Balanced saline solutions (commercially available) will not
destroy sediment structures such as urinary casts.
It appears as though you are substituting the
dilution technique and instead are using a one-drop method which is not
standard practice and, therefore, should be discontinued.1 It
is perfectly acceptable to either dilute using a 10:1 urine
concentration with equal parts of saline and then multiply by two, or
change the urine-sediment concentration to 10:2 and then divide by two.
Both allow for the proper standardization, with the latter allowing for
less manipulation and procedural steps to procure more efficient time
management.1
—G. Berry Schumann, MD
Medical
Director
Schumann Diagnostics
Seymour, CT
References
1. Schumann GB, Friedman SK. Wet Urinalysis,
Interpretations, Correlations and Implications. Chicago, IL:
American Society of Clinical Pathologists, 2003.
Calciums do not agree
Q We have been
experiencing a problem with calcium being run in our laboratory with a
PTH having been ordered for the same patient; the parathyroid hormone
(PTH) is a send-out test for us. The calcium done as part of the PTH is
always a lot higher. Any thoughts?
A It is not surprising
that calcium values from a reference laboratory might not match those
performed in your lab. To investigate the cause, you might start by
looking at proficiency-testing summaries from the CAP or other
providers. There, you can determine whether your analyzer is running
near the mean of the peer group for the method used in your lab.
Assuming it is, then possibly the method used by the reference
laboratory runs significantly higher than your method. You can also
determine this by looking at the differences in means among peer groups.
If you see a significant difference in peer- group means for samples run
on your in-house method and the reference-lab method, then that would
explain the inconsistencies you have described. Even if the
proficiency-test means are not significantly different between methods,
there may still be differences observed in patient samples that are not
seen with proficiency-testing material. The bottom line is that
differences are seen among various calcium assays on chemistry
platforms.
The next question is which (if either) of the two
methods is “right.” Flame atomic absorption spectrometry, or FAAS, is
most often used as a reference method for calcium, though
isotope-dilution mass spectrometry (IDMS) may also be valuable for this
purpose. You should be able to find reference laboratories that perform
one or both of these methods for serum calcium. If the discrepancies are
frequent or if you are concerned about the accuracy of your internal
calcium method, then sending a series of samples to a reference
laboratory for calcium determination by FAAS or IDMS may be valuable. If
your internal method matches one of the reference methods well, then you
may solve the problem by finding a reference lab that either measures
PTH without calcium or uses a different calcium assay. If your internal
method does not match well a reference method, then you could consider
switching to another assay.
—Bradley S. Karon, MD, PhD
Director of Hospital Clinical Labs
Mayo Clinic
Rochester, MN
Daniel M. Baer, MD, is professor emeritus of
laboratory medicine at Oregon Health and Science University in Portland,
OR, and a member of MLO's editorial advisory board.
MLO's “Tips from the Clinical Experts”
provides practical, up-to-date solutions to readers' technical and
clinical issues from a panel of experts in various fields. Readers may
send questions to Dan Baer by e-mail at
[email protected].
