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19
| 1 | 2008
Klinisk Biokemi i Norden
(Fortsætter side 20)
from whole blood, either cell bound or free in plasma.
In both domains, cellular as well as extra cellular, we
shall emphasis pre-analytical as well as analytical chal-
lenges when appropriate. At the very end of this review
we shall speculate as to how these important fields may
develop.
In many ways circulating blood is unique in the
human body. It “travels” several miles every day and
night, and directly or indirectly perfuses every cell of
the body, thus having a unique position to “understand
what is going on in our bodies.” Circulating blood is a
notably dynamic environment involving the turnover
of approximately 1 trillion blood cells daily, including
200 billion red blood cells and 70 billion neutrophilic
leukocytes (2). Nucleated leukocytes which include
lymphocytes, monocytes and granulocytes are the
most transcriptionally active cells in the blood and
thereby targets for both DNA analysis and gene expres-
sion profiling.
The apparent ease of sampling blood makes this
circulatory tissue attractive in trying to understand
disease. For years clinical pathologists and clinical
chemists have drawn whole blood for cell count, hemo-
globin measurements and processed whole blood into
plasma or serum to quantify proteins, hormones and
metabolites. Procedural care has been established in
order to obtain reliable results. Examining for circulat-
ing nucleic acids may pose specific, new problems as
may bio-banking of specimens. When appropriate we
shall address these issues.
Cellular DNA
DNA is the biochemical substance that specifies all
the different parts in living organisms and defines an
individual. All inherited information is specified by
a simple four-letter alphabet, the nucleotides A, G, C
and T, and remarkable, it is the order of these billions
of four nucleotides that constitutes the genome and
encodes all of the instructions necessary to create a
complete organism.
The most well known features of the genome are the
genes, which encode protein products. The Human
Genome Project manifested roughly 33 000 different
genes, comprising only a tiny fraction (~1-3 %) of the
entire human genome (3). Yet it is thought that most
of the functional relevance of an organism is encoded
within the genes and the various regulatory regions
surrounding the genes, although information on non-
coding regions is becoming increasingly interesting.
Foto: Henrik Alfthan. Island.
