Hematology cell
counters continue to provide an ever-broader scope of capabilities.
Technologies that were leading edge a few years ago, such as
reticulocyte enumeration, are now routine. Methods that heretofore
required much manual manipulation—such as CD4 counts—can now be
incorporated as part of the random-access CBC specimen stream on
instruments such as the Abbott Cell-Dyn series.
Food and Drug Administration approval of quantitative nucleated red
blood counts on several instruments now permits automated handling of
patients with a variety of pathologic states.
For 25 years, the holy
grail in the automated counting of the WBC differential has been the
enumeration/quantification of immature granulocytes. This
debate continues with clinical colleagues who
insist they must have a manual differential because they want to know if
"bands" are numerous. It doesn't faze them that study after study
demonstrates that the "band count" is terribly imprecise and non-reproducible.
At least one manufacturer has submitted applications to the FDA for clinical
use of the "immature granulocyte" channel. This advance has great potential
for the precise and accurate quantitation of immature granulocyte forms (the
collective total of promyelocytes, myelocytes, and metamyelocytes).
Ironically, the clinical significance of automated immature granulocyte
counts is difficult to measure at present, since the existing literature is
heavily weighted toward only band counts and not extended immature
granulocyte counts. We do hope to see these immature granulocyte counts take
hold and, finally, eliminate the use of the manual band count.
Siemens reticulocyte
hemoglobin measurement is useful in the early diagnosis of iron deficiency
and in monitoring response to treatment.
Another interesting
new channel is hematopoietic progenitor cells, or HPCs, available on the
Sysmex XE-2100. In some settings, this will permit stem cells to be
quantitated (for example, in an apheresis product) without requiring a
direct CD34 study on a flow cytometer. This study is based on differential
membrane lipid content. HPCs have lower membrane lipid content than mature
leukocytes and are preserved after treatment with a lysing agent.
With increasing
routine automation of assays that previously required the use of flow
cytometers, we may see flow cytometers redirected to more in-depth analyses
of cell structure and function—the emerging field of cytomics.
The rate-limiting step
on the introduction of new diagnostic modalities is no longer a matter of
how quickly the technology can be developed, licensed, and deployed. Far
more important is how quickly medical practitioners embrace the new
technologies and incorporate them into their routines.
Those selecting
hematology instruments can no longer base their decisions solely on the
lowest-price instrument. Medical considerations should
and may dominate. Perhaps the patient mix requires a parameter that
is available only on certain instruments, for example. Operational
considerations may be paramount—reliable, high-throughput, easy-to-use
instrumentation may be more crucial than having all the newest parameters on
a more difficult-to-use instrument. The fiscal effect of eliminating flow
cytometry for high-volume studies, such as CD4 or CD34, may outweigh a
higher cost-per-test on CBCs.
