Proteins in
Blood
and
Urine
Objective
Type of proteins in blood
clinical utility of proteins in blood
and urine
Proteins are important materials and nutrients
in human body. All enzymes, receptors,
membrane channels, Ags, Abs(Igs), coagulation
factors and peotide hormones(GH,prolactin ),…
are proteins in nature. Proteins may be linear
structural(such
as
collagen)
or
globular
functional such as enzymes, hormones …. .
Proteins are polymer of amino acids, formed by
peptide bond between adjacent two amino
acids. Amount of proteins in blood depend on
balance:
rate of synthesis
↔ rate of catabolsim+
clearance.
However, protein distribution between the IV
and EV compartments is also important, so
protein concentrations in blood also affected
by
amounts
of
blood(water)
in
IV
compartment. All protein are synthesized in the
liver, with exception of
complement
systems(by liver and macrophages), and Igs (by
B Lymphocytes of immune system.
Proteins in blood are fractioned and
separated by electrophoresis technique in
which serum but not plasma(presence of
fibrinogen makes the results difficult to be
interpreted) is introduced to filter paper
or acrylamide … etc which is found in PH
8.6. Then electrical current is passed into
media and the protein is separated into:
albumin,
α1-globulin,
α2-globulin,
β-
globulin,
γ-globulin.
The
latter
four
fractions referred to total globulin.
So: Total protein=albumin+total globulin.
Total protein in human is ≈56-86
gr/l,
albumin alone ≈38-51 gr/l. The total
globulin is calculated by subtraction of
total
protein
from
albumin.
The finding of normal total protein does
not excludes the abnormal condition as
the significant decrease of albumin may
be accompanied by significant increase of
total globulin.
Hyperproteinemia and hyperalbuminemia are
rare and of no significant value and may
obtained from prolonged vein stasis during
blood
collection
and
from
excessive
dehydration.
Hypoalbuminemia:
It is important as albumin is one of major
components of osmotic colloid pressure of
blood
vessels
and
so
in
normal
fluid
distribution
and
blood
pressure.
Hypoalbuminemia causes are:
1.
Chronic
liver
disease;liver
cirrhosis
2.
Advanced
kidney
disease;Nephrotic
syndrome
3.
Malnutrition
and
malabsorption
4. Loss through GIT;Enteropathy & skin;
extensive
burns.
Clinical
consequences:
1. oedema due to migration of fluid from IV to
interstitial
compartment
2. transporter and binding capacity defects;
such as for fatty acids, bilirubin, steroid Hs and
drugs which may leads to toxicity with
appropriate dose.
Globulin
Increased in globulin may be due to increased in one
or more of its fractions;α,β, and γ. The α-1 and -2
include :antitrypsin(anti-protease enzymes to limit the
host
enzymes
during
the
infection
period),
haptoglobin(Hb binder during hemolysis to conserve
the body iron), ceruloplasmin, C- reactive protein(CRP,
inflammatory factor), α2- macroglobulin…. etc. The β
includes transferrin, β1-microglobulin….
. The γ
includes the
IgG,M,A,D
and E. The α andβ
components are increased in acute infection while γ
components increased in chronic infection, such as
chronic viral hepatitis.
α2 macroglobulin is the only protein
fraction that increased in end stage of
kidney disease because of its large MW,
while other proteins decreased due to
their
leakage
in
the
urine.
Β1-
microglobulin is marker of tumor as
increased in malignancy of blood cells; in
multiple
myeloma
and
leukemia.
Protein
in
urine
normally less than 150 mg/day of proteins
appear in urine, in kidney disease this
value increased according to degree of
kidney damage which reflect mainly the
glomerular damage. Normally glomerulus
is permeable to proteins of MW ˂60 KD.
In kidney damage(glomerulus) excess
amounts of proteins of large MW˂60 KD
will pass in the urine and may reach 5-50
gr/day.
Presence of low MW of proteins in the
urine indicates the renal tubules damage
as these tubules normally catabolize and
reabsorbe the low MW proteins. In
tubules damage these proteins will
escape from the damaged tubules and
appear in the urine