Biology Reference
In-Depth Information
examined by a pathologist prior to analysis. Blood
can be analyzed as serum or plasma. Is there
a difference in analyzing serum over plasma at
the metabolite level? A recent metabolomics
study showed obvious differences in the GC/
MS chromatograms of plasma and serum taken
from the same healthy human subjects.
16
Of the
72 identi
and 138 females) evaluated the effects of age, sex,
and race on plasma metabolites.
18
The patients
were of Caucasian, African American, and
Hispanic descent and ranged in age from 20 to
65 years. The subjects were divided into three
different age groups; 20
e
35, 36
e
50, and 51
e
65.
Using gas chromatography
e
mass spectrometry
(GC/MS) and liquid chromatography
e
mass
spectrometry (HPLC/MS) methods
ed compounds between the samples,
only 36 were found in both serum and plasma.
Also, the results indicated that some of these
commonmetabolites had different concentrations
in serum and plasma. These results highlighted
the dif
it was
reported that
more than 300 metabolites were
detected of which more than 100 metabolites
were associated, with age, many fewer with sex
and fewer still with race.
“
18
Attention should
therefore be paid to the selection of patients
and controls for a biomarker study and should
not include (a) widely different ages, (b) mix of
men and women, or (c) different ethnicities.
”
culty in comparing interlaboratory results
using different sample types. Generally, the
number of patients and control subjects in pub-
lished studies is very small. For cancer biomarker
discovery, bio
uids and tissues are collected from
a group of patients of different cancer stages and
compared to a group of healthy persons. The
effect of cancer stage on sensitivity of a single
biomarker should be taken into consideration.
12
Sample Collection, Handling, and Storage
Samples are collected from persons who have
had a physical examination by a physician who
determines that the person of interest has the
disease or is healthy. Samples should be
collected in clean freezer type tubes and stored
in a freezer immediately until time of analysis.
Hsieh et al. showed that using different blood
collection tubes affects the observable proteome
of serum and plasma.
14
At the time of analysis,
samples should be thawed on ice or room
temperature and prepared according to the
selected method of analysis. The history of the
sample is very important; blood and tissue
samples used in search of biomarkers may
have been obtained from sample storage banks
without proper collection, storage, and informa-
tion about the age and condition of the patient
and, if there is cancer present, the stage of the
disease. Also, the storage periods may be
different. A lack of consistency in sample selec-
tion, collection, handling, and storage can
doom any study to failure before data collection.
One issue that is of constant concern in the
analysis of serum or plasma samples is the
method of collection, preparation, and storage.
Number of Samples
The number of samples analyzed in a
biomarker discovery study should be suf
cient
to give statistically signi
cant results between
the sets of samples being compared. This
number may vary from 25 to 100 samples in
a set; the larger the numbers of samples the
more accurate the statistical results. However,
for an epidemiological or validation study the
number of diseased samples and controls can
be in the hundreds or thousands. Unfortunately,
most published biomarker discovery studies
only tested a limited number of clinical samples.
Ethnicity, Sex, and Age
Today, a study is normally carried out using
bio
uids or tissues collected from patients and
healthy subjects of different ages, sex, and race.
Using samples from patients and controls that
are of different ages and sex can in
uence the
results. A recent study of 269 subjects (131 males
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