Full text of DOI:10.1111/j.1939-165X.2002.tb00288.x

Blood Values of Juvenile Northern Elephant Seals
(
Mirounga angustirostris) Obtained Using a Portable
Clinical Analyzer
R. Scott Larsen, Martin Haulena, Carol B. Grindem, Frances M. D. Gulland
Background — Sick, injured, or orphaned juvenile northern elephant seals (Mirounga angustisrostris) treated at rehabilitation cen-
ters frequently present with abnormalities in blood sodium, potassium, chloride, BUN, and glucose concentrations, and HCT.
These abnormalities could be detected rapidly using a portable blood analyzer, but the results with this analysis method do not
necessarily equate with those obtained using other techniques. Objective — The objective of this study was to better assess the
clinical relevance of blood values obtained from a portable analyzer and to compare the results with values obtained using more
common methods of analysis. Methods — Heparinized whole blood samples were collected from 20 rehabilitated juvenile north-
ern elephant seals. A portable clinical analyzer (i-STAT, i-STAT Corp, East Windsor, NJ, USA) was used to establish baseline val-
ues. Serum biochemical values were obtained using an automated chemistry analyzer (Olympus AU5200, Olympus America,
Melville, NY, USA). HCT was determined using EDTA whole blood and a cell counter. Results — Using the portable analyzer,
mean (minimum-maximum) values were obtained for sodium, 143 (132-146) mmol/L; potassium, 4.4 (3.9-5.8) mmol/L; chloride, 106
(
101-109) mmol/L; BUN, 1.8 (1.1-2.4) mmol/L; glucose, 7.55 (5.99-8.49) mmol/L; and HCT, 0.55 (0.52-0.61) L/L. Average differences
between methods were small for potassium (–0.45 mmol/L), BUN (0.1 mmol/L), and HCT (0.037 L/L) but were large for sodium
–6.8 mmol/L), chloride (–6.4 mmol/L), and glucose (–0.56 mmol/L). Conclusions —These results suggest that the i-STAT portable
(
analyzer could be useful for clinically assessing juvenile elephant seals. However, when making medical decisions, the clinician
should be aware of differences associated with various analyzers and sample types. (Vet Clin Pathol. 2002;31:106-110)
Key Words: Electrolytes, elephant seal, glucose, hematocrit, i-STAT, Mirounga angustirostris, point-of-care, portable analyzer
———◆———
Every year, many sick, injured, or orphaned pinnipeds
are treated at rehabilitation centers in the United States.
Juvenile northern elephant seals (Mirounga angustis-
tion. However, the blood analysis methods reported for
pinnipeds usually use serum for biochemical analysis
and use blood mixed with EDTA for hematology. If
portable analyzers are to be used for pinnipeds, it is
important to identify differences in reference intervals
that may result from the use of different analyzers or
samples. We used a portable analyzer to determine
sodium, potassium, chloride, glucose, BUN, and HCT
values for juvenile elephant seals. These values were
compared with those obtained with matched blood
samples using serum for biochemistry analysis, and
blood in EDTA for HCT.The mean difference (and asso-
ciated SD) between the 2 methods was compared for
1-3
rostris) are one of the most common species treated.
Stranded pinnipeds often present with severe metabol-
ic disease, including renal failure, hypoglycemia, elec-
trolyte abnormalities, acidosis, dehydration, shock, star-
2,4-6
vation, gastrointestinal hemorrhage, and anemia.
Immediate identification of these disorders by rapid
determination of electrolyte, glucose, BUN, and HCT
levels could be life-saving. Small, portable point-of-care
clinical analyzing systems have recently been developed
that can be used to measure these values quickly and
easily, expediting the acquisition of laboratory data in
critical care situations. Results of studies in humans
beings and domestic animals indicate that portable clin-
11
each blood constituent.
Materials and Methods
7-10
ical analyzers can provide reliable data.
Point-of-care analyzer systems commonly recom-
mend the use of heparinized whole blood for analysis.
Methods that use whole blood or plasma are preferred
for emergency laboratory work because samples can be
immediately processed without waiting for clot forma-
Between January and April 2000, approximately 70
stranded northern elephant seal pups were transported
to the Marine Mammal Center (Sausalito, Calif, USA)
for medical treatment, supportive care, and rehabilita-
tion. In May 2000, 20 of these seals were evaluated to
From the Environmental Medicine Consortium, Department of Clinical Sciences (Larsen), and the Department of Microbiology, Pathology, and
Parasitology (Grindem), College of Veterinary Medicine, North Carolina State University, Raleigh, NC; the North Carolina Zoological Park, Asheboro,
NC (Larsen); and the Marine Mammal Center, Sausalito, Calif (Haulena, Gulland). Corresponding author: R. Scott Larsen, DVM, MS, Veterinary
Medical Teaching Hospital, University of California, One Shields Ave, Davis, CA 95616 (slarsen@ucdavis.edu).
Page 106
Veterinary Clinical Pathology
Vol. 31 / No. 3 / 2002

Larsen, Haulena, Grindem, Gulland
determine whether they were fit for release. Determin-
laboratory personnel. Laboratory quality control (QC)
was performed, with calibration on every lot of samples
and also every 24 hours. Once per month, blind studies
were conducted, and QC values, methods, and ranges
were reviewed. Blood from the EDTA tube was used to
determine HCT using an automated cell counter (Vet
ABC, Heska Corporation, Fort Collins, Colo, USA). The
cell counter had previously been calibrated for marine
mammal RBCs. Calibration had been established by
comparing cell counter results from juvenile elephant
seals (n=19) with HCT values obtained using microcen-
trifugation. For elephant seals, values from the cell
counter were 0.011 (± 0.011) L/L higher than manually
spun results (J. Lawrence, Marine Mammal Center, per-
sonal communication).
ation of an animal’s suitability for release was based on
clinical assessment, physical examination, and evalua-
tion of CBC and serum chemistry results.
At the time of sampling, the seals weighed 67 ± 6 kg
and were estimated to be 4-5 months old. They were
manually restrained, and blood was drawn from the
epidural intravertebral vein into a collection tube coated
with lithium heparin (Vacutainer, Becton Dickinson,
Franklin Lakes, NJ, USA) using Monoject needles (20 ga
by 3.8 cm) and adapters (Sherwood Medical, St Louis,
Mo, USA). Lithium heparin was chosen over sodium
heparin so electrolyte analysis would not be altered by
the electrolytes in the heparin medium. Samples were
analyzed within 10 minutes with the portable clinical
analyzer (i-STAT, i-STAT Corporation, East Windsor, NJ,
USA) by introducing heparinized whole blood (approx-
imately 65 µL) into a disposable cartridge (i-STAT 6+, i-
STAT) designed for simultaneous assay of electrolytes,
glucose, BUN, and HCT. Each cartridge contains a series
of thin-film electrodes (biosensors) that contact the
blood sample and send signals to an electronic system.
The system compares these signals with calibration sig-
nals contained within the cartridge and processes the
Mean, SD, median, 25th percentile, 75th percentile,
and minimum and maximum values for each blood ana-
lyte using each method of analysis were determined.
The mean (± SD) difference between values obtained for
the same sample (value from the portable analyzer
minus the value from the automated analyzer) were
determined for all analytes.The intervals of values from
the 2 methods were compared with previously reported
4
intervals for juvenile elephant seals.
12
results. Sodium (mmol/L), potassium (mmol/L), and
chloride (mmol/L) values were measured by direct ion-
Results and Discussion
12
selective electrode potentiometry. Glucose was mea-
sured by oxidation with glucose oxidase and ampero-
Sodium values from the portable analyzer were slightly
lower than those previously reported, but values from
1
2
metric measurement of hydrogen peroxide. Urea
BUN) was hydrolyzed to ammonium in a reaction cat-
alyzed by urease, and the resultant ammonium ions
4
(
the automated analyzer were slightly higher (Table 1).
Portable analyzer values were 4-10 mmol/L less than
those from the automated laboratory instrument, sug-
gesting that sodium values obtained with the 2 tech-
niques cannot be considered equal. Equating the 2 mea-
surements could cause a clinician to make an erroneous
diagnosis of pinniped hyponatremia (sodium < 147
11
were measured amperometrically. Values for glucose
and BUN were reported by the analyzer as mg/dL;
results were then converted to mmol/L. HCT (L/L) was
12
determined by conductivity.
At the same time that the heparinized sample was
taken, a second blood sample was collected from each
patient into a plain red-top glass tube (Vacutainer) and
into a tube containing EDTA (Vacutainer). These sam-
ples were kept refrigerated and were processed by
trained laboratory personnel within 1 hour of sample
collection. The samples in the plain tubes were allowed
to clot, centrifuged at 3100g for 10 minutes, and then
serum was extracted using a pipette. Serum concentra-
tions of sodium, potassium, chloride, BUN, and glucose
were measured using an automated analyzer (Olympus
AU5200, Olympus America, Melville, NY, USA). Sodi-
um, potassium, and chloride concentrations were deter-
mined by indirect ion-selective electrode potentiometry.
6
mmol/L) and could lead to inappropriate treatment.
The cause for the discrepancy probably is related to the
use of heparinized whole blood rather than serum in the
portable analyzer. Elephant seal RBCs have relatively
high intracellular sodium concentrations relative to ter-
14
restrial mammals, and some of this sodium is released
when blood samples are spun for serum extraction.
However in a previous study in domestic dogs, there
was poor correlation for sodium values between the i-
STAT and an automated chemistry analyzer, even when
10
heparinized whole blood was used for both machines.
Therefore it is prudent to interpret laboratory values,
especially sodium values, using appropriate specimen
and instrument-derived reference intervals.
13
Glucose was measured using the hexokinase method.
BUN was determined colorimetrically with reductive
amination of 2-oxoglutarate by glutarate dehydrogenase
oxidation using ammonia generated by urea degrada-
tion with urease.The samples were processed by trained
Both techniques produced potassium values com-
parable to previously reported serum potassium values
for elephant seals (Table 1). However, potassium con-
4
centrations from the portable analyzer were 0.45 (± 0.43)
Vol. 31 / No. 3 / 2002
Veterinary Clinical Pathology
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Blood Values in Elephant Seals
Table 1. Biochemical values for juvenile northern elephant seals obtained from whole blood using a portable analyzer (i-STAT) and from
serum using an automated analyzer (Olympus AU5200). Hematocrit values were obtained from whole blood using the portable analyzer
and from EDTA blood using a cell counter (Vet ABC).
Analyte
n
Method Mean ± SD
Difference
SD*
Median
25th
75th
Min–Max
Published
Min–Max
†
±
Percentile Percentile
Sodium (mmol/L)
20 i-STAT
Serum
143±3
144
150
4.4
143
149
4.1
145
152
5.1
132-146
147-156
3.9-5.8
151±2
–6.8±3.2
–0.45±0.43
6.4±3.2
143-154
4.7-6.1
Potassium (mmol/L)
Chloride (mmol/L)
BUN (mmol/L)§
Glucose (mmol/L)§
HCT (L/L)
20 i-STAT
Serum
19‡ i-STAT
4.7±0.6
5.1±0.5
106±3
5.0
4.8
5.3
4.4-6.2
106
100
1.7
103
98
108
100
2.1
101-109
97-104
Serum
100±2
98-107
20 i-STAT
Serum
1.8±0.4
1.7±0.3
7.55±0.67
8.55±1.67
0.55±0.04
0.52±0.03
1.5
1.1-2.4
0.1±0.2
1.7
1.5
1.9
1.1-2.1
1.2-2.1
20 i-STAT
Serum
7.60
8.05
0.54
0.52
7.27
7.55
0.53
0.50
7.77
8.60
0.57
0.54
5.99-8.49
6.33-10.43
0.52-0.61
0.48-0.54
–0.56±1.06
0.037±0.004
7.10-10.49
0.46-0.61
20 i-STAT
Serum
*
Difference = mean value from the portable analyzer – mean value from the automated analyzer.
†
Results from 25 juvenile elephant seals.4
‡
§
A chloride value was not obtained for 1 sample.
Glucose and BUN values were converted from mg/dL to mmol/L.
mmol/L less than those obtained from the automated
analyzer. In humans, whole blood potassium concentra-
tions are typically 0.1 to 0.7 mmol/L lower than serum
concentrations due to the release of potassium from
similar to each other and similar to previously reported
values in elephant seals (Table 1). Differences between
4
BUN values obtained with these 2 techniques were
small, and the values were considered equivalent.
The glucose values obtained using the portable ana-
lyzer and the automated analyzer were both slightly
lower than previously reported values for healthy ele-
15
ruptured platelets during coagulation. The difference
between sample types likely accounts for the difference
in potassium values observed in the elephant seals,
however it should be noted that in a previous report of
portable analyzer use in domestic animals a 0.5-1.5
4
phant seals (Table 1). However, values from the auto-
mated analyzer were slightly higher overall than those
from the portable analyzer. Whole blood samples were
processed on the portable analyzer within minutes of
sampling, whereas serum samples were processed on
the automated analyzer up to 1 hour later. With human
samples, glucose values would be expected to be lower
in serum than in immediately processed whole blood,
because of glycolysis during prolonged contact of blood
8
mmol/L difference in potassium also was observed.
Chloride values for both techniques were similar to
4
previously reported values, although results from the
portable analyzer were consistently higher than those
from the automated analyzer (Table 1). The cause of the
large difference in chloride values in this investigation is
unknown, but may relate to the different sample types
used. The portable analyzer has been reported to over-
4
cells with serum. However in elephant seals, glucose
7-9
estimate whole blood chloride in other species. The
mean difference was larger in elephant seals (6.4
mmol/L) than that reported in human beings (1.9-5.5
mmol/L), dogs (3.6 mmol/L), cats (2.3 mmol/L), and
uptake and glycolytic rates are slow and heparinized
blood samples can be stored for several hours without
16
significant decreases in plasma glucose concentration.
In fact, glucose concentration may actually be higher in
plasma or serum than in whole blood. Although the glu-
cose concentration is the same in the water of plasma
and the water of RBCs, the RBCs contain more protein
7-9
horses (2.0 mmol/L). Discrepancies in chloride values
have been attributed to the narrow range of values for
7
chloride and to the sensitivity of chloride ion-selective
9
13
electrode systems to the effects of protein. Thus the
and consequently have a lower concentration of water.
large difference in chloride observed here may be due to
both sample and machine effects.
This lower concentration of water may cause a dilution-
al effect, making the concentration of glucose in whole
blood lower than that in serum or plasma. We do not
13
BUN values obtained with the 2 techniques were
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Veterinary Clinical Pathology
Vol. 31 / No. 3 / 2002

Larsen, Haulena, Grindem, Gulland
know whether this dilution effect accounts for the dis-
crepancy between the portable and automated analyzer
results; however, in human beings and domestic ani-
mals, portable analyzer results for glucose differ sub-
These properties are quite different for seal and human
21
blood, so the higher volume fraction of elephant seal
RBCs results in increased conductivity and, consequent-
10
ly, increased HCT values.
17-19
stantially from the results of automated analyzers.
The results of this study suggest that the i-STAT
portable clinical analyzer could be useful for evaluating
elephant seals in critical care situations. However, some
values obtained with the portable analyzer depart sub-
stantially from those determined with serum processed
on an automated analyzer. Much of this variation may
be associated with differences in sample type. It is more
appropriate to use a reference interval from portable
analyzer values that are obtained from healthy animals
of a given species rather than directly comparing
portable analyzer values to those obtained using other
methods. Individual laboratory-derived reference inter-
vals are not generally available for marine mammals
and other wildlife species, as they are for domestic ani-
mals; therefore, appropriate use of published intervals
is very important. The minimum and maximum values
reported in this investigation are narrow because the
animals were of similar ages and were kept in similar
environments. However, these values serve as a starting
point for defining reference intervals for portable ana-
lyzers in young elephant seals.Values reported here are
only for juvenile elephant seals, but seals of this age
group are most commonly encountered in clinical set-
HCT results from the 2 methods were similar and
were within reference intervals previously reported for
4
juvenile elephant seals (Table 1), however values from
the portable analyzer were an average of 0.037 L/L high-
er than those obtained from the cell counter. A 0.04 L/L
difference between methods has been reported for
9
human blood, and a 0.05 L/L difference has been re-
10
ported for dogs, cats, and horses. Other investigators
have reported on the variability of pinniped HCT val-
ues, which can be affected by laboratory methodology,
6,20
age, and animal handling technique.
For example,
electronic cell counters calculate the HCT using the
measured RBC count and MCV. Most pinnipeds have
relatively large RBCs, and elephant seals have MCV val-
4
ues of 170-185 fl. As a result, the RBC count, MCV, and
HCT values are accurate for pinnipeds only if those
parameters are measured using a calibrated cell counter
4
to account for the larger size of marine mammal RBCs.
In a previous study, HCT measurements by a cell coun-
ter were 4-15% higher than those obtained by microcen-
trifugation; however, the cell counter used in that inves-
20
tigation had not been calibrated for pinniped RBCs. In
contrast, the cell counter used in this investigation had
previously been calibrated for pinniped RBCs, and the
HCT measurements obtained were only 0.011 (± 0.011)
L/L higher than values obtained by microcentrifugation
2
tings. ◊
Acknowledgments
The authors thank the veterinary technicians, husbandry staff,
and volunteers of the Marine Mammal Center, including L.
Phoenix, J. Lawrence, J. Sicree, D. Wickham, and P. Labelle.
(
J. Lawrence, personal communication). Both the cell
counter and the portable analyzer rely on the rheologic
properties of RBCs, and the conductivity of blood is
greatly dependent on the volume fraction of RBCs.
© 2002 American Society forVeterinary Clinical Pathology
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