Q. Our hospital laboratory policy requires a repeat analysis of any critical
values obtained by chemistry or hematology instrumentation. Our hematology
analyzer samples the specimen once, then splits the sample into four parts and
measures white blood cells in two channels by different methodologies.
Hemoglobin is measured directly in one channel and is calculated from measured
red blood cell values in another channel. The instrument performs various
comparisons of values from each channel for verification.

With today's short labor supply and dwindling reimbursements, is it necessary to
repeat critical WBC or hemoglobin results? One issue not addressed by
double-channel analyses might be the poorly mixed specimen resulting in a
diluted or concentrated sampling (when the automated sampling tray is not used).
Is it necessary to rerun critical WBC and Hgb results in this setting?

A. No regulatory requirement exists for automatic repeat analysis of critical
values. As you pointed out, modern hematology analyzers are designed to detect
interferences that may render a result unreliable, resulting in a flag being
generated. Such flags might then warrant repeat analysis or additional manual
review or troubleshooting, depending on the nature of the flag. The important
point regarding critical values is that they require some sort of intervention
to ensure the validity of the result. While repeating the analysis is not an
inappropriate procedure, it may not always be necessary.

In your situation, in which a sample is mixed poorly, the results produced by
the instrument will be internally consistent, so a flag will not be generated.
However, if this is occurring at a substantial frequency in your laboratory,
this problem may not be restricted to samples that generate critical values. All
results would be suspect, and limiting repeats to only samples with critical
values makes little sense. Instead, the logical extreme of this approach would
be to replicate analyses of all samples. This, of course, is not only
impractical but also medically unwarranted. A better approach would be to take
steps to ensure that improperly mixed samples occur at an acceptably low rate.
Introducing quality assurance measures into your processes at critical analytic
checkpoints is much more efficient than attempting to catch errors at the output
stage.

A reasonable approach to address your specific question would be to
retrospectively or prospectively review the results of replicate analyses of
your critical values and document the frequency with which spurious results were
produced without your instrument generating flags. If this is an infrequent
event, you can easily justify discontinuing your policy to replicate analyses of
all critical values. What constitutes an acceptable error rate is a subjective
decision for a medical director based on various local factors. If you find you
have a problem with improperly mixed samples, I would recommend that you
critically evaluate your processes to isolate the cause of the problem and
adjust your procedures accordingly.



Steven Kroft, MD
Department of Pathology
University of Texas Southwestern Medical Center
Dallas

Vice Chair, CAP Hematology/Clinical Microscopy Resource Committee


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