Quality of skin puncture CBC
Q We have clinics where nurses are collecting and
running CBCs on a Coulter using fingersticks only, which can result in a
less than optimal sample. Even though the nurses have been trained on
collection and other processes, many of the samples they run through the
machine have erroneous results, probably due to clots or excessive
squeezing of the puncture site. Is there any information we can show the
nursing staff and physicians that states it is preferable to run CBCs
from a venipuncture rather than a fingerstick?
A A complete blood count (CBC) and other blood
parameters can be obtained from blood collected by either venipuncture
(venous blood) or skin puncture (fingerstick or heelstick; capillary
blood). Adhere to the recommendations of the manufacturer of the
specific analyzer. No explicit recommendations stating the superiority
of one method over the other are made by the Clinical and Laboratory
Standards Institute (CLSI), with certain exceptions. CLSI states, “Blood
specimens obtained by skin puncture are especially important in
pediatrics, because small but adequate amounts of blood … can be
Venipuncture used to obtain blood for analysis is
potentially dangerous in infants. Furthermore, “It is also advantageous
to obtain skin puncture specimens from some adult patients.”1
This includes severely burned, extremely obese, and geriatric patients,
along with patients with thrombotic tendencies, inaccessible superficial
veins or fragile veins, and patients performing tests at home or tested
at point-of-care. This list implies that in most adult patients the
preferred method of obtaining a blood sample is venipuncture.
It is preferable to run CBCs from a venipuncture
rather than a fingerstick due to following reasons:
a) Venipuncture provides for larger blood-specimen
b) The technique of venipuncture appears to be less
prone to producing a suboptimal specimen due to its less complicated
character. There is, for instance, the requirement to have the
disinfectant completely air dried before proceeding. If this is not
adhered to, significant hemolysis may occur, which will distort the
results of a smaller (skin puncture) blood volume much more severely
that those of a large (venipuncture) volume. It is also paramount to
discard the first blood drop in skin puncture, since it will be diluted
by extracellular fluid. Squeezing of the puncture site is to be avoided
because it causes hemolysis and dilution by extracellular fluid.
c) Another reason to prefer venipuncture (in adults)
may be the fact that reference intervals were most likely determined
using this method. There are controversial results concerning different
CBC values and chemistry parameters between fingerstick and venipuncture
blood. The CLSI guidelines show that some chemical constituents have
values in capillary blood that differ from those in venipuncture blood.
One study shows no significant differences between capillary and venous
blood values for numerous parameters included in the CBC,2
whereas other authors find significant differences.3
d) Venipuncture samples provide more reliable
results, since all these studies have shown that venous-blood results
have less variation and better precision.
In summary, venipuncture is the preferred method of
blood sampling in most adult patients. If an erroneous CBC result is
suspected and post-collection (laboratory) problems have been ruled out
by adequate QC and QA procedures, venipuncture is recommended.
— Winfried Reichelt, MD, PhD
— Guang Fan, MD, PhD
Oregon Health and Science University
- Clinical and Laboratory Standards Institute.
Procedures and devices for the collection of diagnostic capillary
blood specimens; Approved Standard – Fifth Edition. Wayne, PA:
CLSI; 2004: Vol. 24, No. 21.
- Stuart J, Barrett BA, Prangnell DR. Capillary
blood collection in hematology. J Clin Pathol.
- Yang Z-W, Yang S-H, Chen L, Qu J, Zhu J, Tang Z.
Comparison of blood counts venous, fingertip and arterial blood and
their measurement variation. Clin Lab Haematol.
Differentiating cells in UA
Q In our urinalysis lab, we have some difficulties in
the differentiation of renal epithelial cells from transitional
epithelial cells. Even when reading more information about them and
looking at photos from different atlases, we still have doubts. We read
that sometimes it will be difficult to differentiate, especially for cubidal renal epithelial. The origin of the cell is another factor. We
also correlate with other findings in the urinary sediment. Is it
acceptable to report the quantity of “non-squamous epithelial cells”
when doubts arise? What do you recommend?
A Renal cells are difficult to identify accurately in
wet-microscopic urinalysis and can often be mistaken for leukocytes,
histiocytes, granular casts, deep urothelial cells, and squamous
metaplastic cells. There are important differences between renal
epithelial cells and deep urothelial cells that relate to the shape and
texture of the cytoplasm.
Deep urothelial cells are round, have a centrically
located nucleus with a cytoplasm that is often homogenous and displays
an endo-ectoplasmic rim. Renal cells are polygonal, elongated, as well
as a variety of shapes, with a central or eccentrically located nucleus
and a cytoplasmic texture that can be finely granular to coarsely
granular. The origin of
renal cells cannot be determined in wet-microscopic urinalysis and
requires confirmatory methods such as cytodiagnostic urinalysis to
characterize the renal-cell types and their origins.1
It is important to state “suspect renal cells”
on the report form or in discussions with the pathologist or requesting
physician. Therefore, stating “non-squamous epithelial cells present” is
inadequate and can be misleading. Without accurately reporting suspect
renal cells, clinical laboratory scientists will never be able to
properly detect and prevent the early stages of renal failure.
— G. Berry Schumann, MD (deceased)
Former medical director at Schumann Diagnostics
- Schumann GB, Friedman SK. Wet Urinalysis,
Interpretations, Correlations and Implications. Chicago, American
Society of Clinical Pathologists, 2003.
Tube type for plasma samples
Q I have a blood bank question. According to the AABB
technical manual, you can use either serum or plasma for antibody
screening and cross matching. They do not mention the tube type. We
occasionally get patients with a lot of fibrin and have to pre-warm; if
we could use plasma, it would avoid that procedure. Can you help me find
where it indicates tube type?
A The question appears to ask what tube type is best
for preparing plasma samples for antibody screening and cross matching.
As the questioner points out, the AABB technical manual states that such
testing can be done using either serum or plasma.1 In most
cases plasma is sufficient, except, for example, in some adsorption
studies and would be necessary in testing that required complement such
as the Donath-Landsteiner test.
In addition, the use of plasma can simplify testing
by avoiding formation of clots. In most cases, our lab prefers to use
plasma obtained from EDTA collection tubes.
Although the AABB does not specify a particular tube
type, the Food and Drug Administration(FDA) does require the tubes used for
immunohematology testing to be cleared for that use by the FDA (i.e.,
510(k) compliant). Recently, this has meant that plastic tubes, which
have often been instituted for safety reasons, must be compared to prior
Even when tubes are 510(k) certified, additional
validation testing should be performed in-house to ensure a new tube
type will work under conditions in a particular lab.
Few studies have been done to compare specific tube
types in the literature. Anderson and colleagues performed a study
specifically comparing plastic and glass test tubes from one
manufacturer for plasma and serum collection. They showed the two tube
types to be in agreement for ABO and Rh typing.2 Similar data
can also be found on the FDA website and from test-tube manufacturers.
Serum-separator tubes should be specifically avoided
in performing immunohematology testing due to issues of false-positive
results.3 A synopsis of issues related to the use of this
system can be found at the e-Network Forum of the California Blood Bank
— Eapen K Jacob, MD,
Transfusion Medicine Fellow
— Brenda Bendix, MT(ASCP) SBB,
Reference Laboratory Supervisor
— Jeffrey L. Winters, MD,
Division Transfusion Medicine
Department of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine
- Shulman IA. Pretransfusion Testing. In: Roback JD
CM, Grossman BJ, Hillyer CD, eds. Technical Manual, 16th ed.
Bethesda: AABB, 2008.
- Anderson DR, Wiseman J, MacLeod J, et al.
Evaluation of polyethylene terephthalate for ABO and Rh typing and
alloantibody screening. Transfusion. 2000;40(6):669-672.
- Geisland JR, Milam JD. Spuriously positive direct
antiglobulin tests caused by use of silicone gel. Transfusion.
- Shulman IA, ed. In: California Blood Bank Society
e-Network Forum: www.cbbsweb.org/enetcommun.html. Accessed:
May 13, 2009.
Escherichia coli in urine specimens
Q We have a relatively small hospital and micro lab but
do test for shiga-toxin-producing E coli (STEC) in stools. We are
currently testing within Centers for Disease Control and Prevention
recommendations. My question: Is there significance in finding
O157 in urine specimens? We have an occasional urine isolate panel
that pops up an alert for possible E coli O157. We send these
isolates out to the state lab for shiga testing, and they have always
come back as negative for shiga toxin. We do not do shiga-toxin testing
on urines here and wondered if we need to continue with sending them
out. Any thoughts?
A Many automated instrumentation will alert to possible
E coli O157 in their identification schemas. E coli O157 and the other shiga-toxin-producing
E coli serogroups, however, are found only in the
gastrointestinal tract, not in the urinary tract.
The profound effects of infection with a shiga-toxin-producing
E coli, including hemolytic uremic syndrome (HUS), come
from the cytotoxins (shiga toxins) produced by these organisms. It is
the shiga toxins that cause the disease in the gastrointestinal tract,
not the presence of the organism itself. The toxins may bind to
leukocytes and be distributed throughout the bloodstream. Endothelial
cells can be affected by these bloodborne toxins leading to HUS.1
You should not need to send urinary isolates for shiga-toxin testing.
— Susan E. Sharp, PhD, DABMM
Director of Microbiology
- Donnenberg MS. Enterobacteriaceae. In:
Principles and Practices of Infectious Diseases. 6th ed. Mandell
GL, Bennett JE, Dolin R, eds. Elsevier Churchill Livingstone.
Philadelphia, PA; 2005:2576-2577.
Brad S. Karon, MD, PhD, is assistant professor of
laboratory medicine and pathology, and director of the Hospital Clinical
Laboratories, point-of-care testing, and phlebotomy services at Mayo
Clinic in Rochester, MN.