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NUTRITIONAL ASSESSMENT AND PROFILING: BIOCHEMICAL
Introduction
Different biochemical methods of assessment of dietary status can provide data that
may reflect a person's recent dietary intake or long-term intake, or it may not reflect
intake at all
...
These include
activity level, stress, age, gender, and the status of other nutrients
...
A good test should be sensitive to changes in
status of a nutrient and be minimally influenced by other factors
...
Clinical
nutrition assessment, as done in hospitalized settings, is described here, although it
is performed using a combination of methods
...

 Aplastic anemia - A form of anemia that exhibits a deficiency in all elements of
the blood, aplastic anemia can be caused by exposure to toxic chemicals,
radiation, or medications
...
The symbol for deciliter is dL
...
The symbol for gram is g
or gm
...


 Hemochromatosis - A hereditary disorder in which there is an excessive
absorption and storage of iron
...

 Hemoglobin - A substance in red blood cells that is responsible for its color
...
Hemoglobin
transports oxygen through the blood
...
This usually leads
to anemia
...
The three major types of leukocytes are granulocytes, lymphocytes, and
monocytes
...

 Linoleic acid - One of the unsaturated fatty acids that are essential for growth
but cannot be synthesized by the body
...

 Linolenic acid - An essential fatty acid
 Liter - A unit of volume equal to the volume occupied by one kilogram of water
at 4 degrees Celsius and 760 millimeters of mercury pressure
...

 Megaloblastic anemia - A form of anemia that is characterized by abnormally
large red blood cells
...

 Microcytic anemia - A form of anemia that is characterized by abnormally small
red blood cells and low circulating levels of hemoglobin
 Micrograms - A millionth of a gram
...

 Micromoles - A unit of measure that is one millionth of a mole
...

 Milligrams - A thousandth of a gram
...

 Nanograms - A billionth of a gram
...

 Nephrosis - A degeneration of the outer tissue of the kidney tubules
...
The symbol is pg
...

 Reticuloendothelial - This adjective refers to cells known as phagocytes, such
as macrophages and monocytes
...

 Retinol - A lipid alcohol that functions in the retinal of the eye
...

Sometimes the terms are used synonymously but retinol is actually the 'preformed
vitamin A' found in animal products
...
This can occur in kidney failure when the kidney
cannot excrete the waste products in the urine
...
The excess copper may be deposited in the liver,
causing jaundice and cirrhosis, or in the brain, causing mental retardation
...
The corneal and conjunctiva become dry and thickened
...


Iron
None of the routinely available tests reflects iron intake; rather, they assess body stores
...
Iron absorption is dependent on dietary factors such as
food source and the ascorbic acid content of the meal
...
Because the iron pool is
associated with hemoglobin, persons with a larger blood volume (and thus more
hemoglobin) have larger stores of iron
...

Serum iron and iron-binding capacity
Serum iron is largely bound to the beta-globulin transferrin
...
Iron
is passed from the reticuloendothelial cells to the plasma where 50% is turned over in
one hour
...
Normal adult levels of serum iron range from 65-200 micrograms per

deciliter (mcg/dL)
...
High serum iron levels are seen
in cases of megaloblastic anemia, when inflow into the plasma is increased, and in cases
of aplastic anemia, when outflow from the plasma is decreased
...
Levels are decreased with chronic disease, protein deficiency, or hepatic
disease
...

Low serum iron and low iron-binding capacity are the best indicators of anemia of chronic
inflammation
...
Serum
ferritin levels are thought to reflect body stores
...
Lower values are
indicative of iron deficiency with anemia
...
High levels are seen with
hemochromatosis and transfusions
...

Free Erythrocyte Protoporphyrin (FEP)
Protoporphyrins cannot be utilized for the synthesis of heme during iron deficiency; thus
they will be found in higher levels when a patient is iron- deficient
...


Zinc
There is no reliable method of assessing zinc stores
...

Plasma Zinc
A change in plasma zinc does not occur until zinc intake is extremely low
...
Most is bound to alpha2-

macroglobulins or to albumin
...
Other factors that influence plasma zinc are stress, infection, and hormones
...

Zinc Tolerance Test
This test measures the change in plasma zinc after zinc is orally administered
...

Hair Zinc
Hair zinc levels of less than 70 mcg per gram (gm) have been associated with clinical
signs of marginal zinc deficiency, such as impaired growth and poor appetite, in children
...

Taste Acuity Tests
Decreased taste acuity is a symptom of zinc deficiency in both children and adults
...
The test is based on the detection and
recognition thresholds for each taste quality
...

Plasma contains only a small amount of the total body store of copper, and so plasma
copper is not a very good indicator of body stores; while plasma copper does detect
severe copper deficiency, it is not sensitive to marginal copper status
...

Plasma copper levels can decrease in nephrosis, Wilson's disease, and protein-energy
malnutrition
...
It functions as ferroxidase, an enzyme that oxidizes ferrous to

ferric ion and influences the flow of iron from cells to plasma
...
Ceruloplasmin levels increase with estrogens, and decrease in
Wilson's disease, uremia, and nephrosis
...
Levels of this
enzyme fall during copper deficiency; thus testing for the enzyme's activity is considered
a sensitive indicator of copper depletion
...

Urinary Copper
Urinary copper excretion does not vary much with changes in copper intake and
therefore is not a useful measure of copper status
...

Normal selenium levels of the U
...
population fall within the range of 2
...
29
micromoles (mcmol) per liter (L)
...
A new technique that can be used to analyze serum, plasma
or whole blood selenium is called graphite furnace atomic absorption spectrometry
...

Urinary Excretion

Urine samples reflect selenium content of the previous meal and are not useful for
assessment of selenium status, though they can be used to detect toxicity
...
Selenium is
incorporated into toenails as they grow
...

Glutathione Peroxidase Activity
There is a correlation between blood glutathione peroxidase activity and blood selenium
up to 1
...
Beyond that point the activity plateaus, and cannot be used to
determine selenium status
...
Such factors include age, sex, ethnicity, iron-deficiency
anemia, essential fatty acid deficiency, and vitamin B12 deficiency
...
Provitamin A carotenoids are dietary
precursers of retinol
...
A measure of liver stores would be the best index for vitamin A status, but
such measurements are not practical
...
Thus experts advise using a combination of
measures from different techniques
...
Serum
retinol levels remain constant until liver stores are severely depleted or contain an
excess amount
...
Normal
serum vitamin A levels hit above 20 mcg/dL
...
Excessive intakes
of vitamin A can result in levels over 65 mcg/dL
...


Low-fat diets can impair the absorption of vitamin A because fat is needed for its
absorption
...
Ingestion of vitamin A does no effect serum
levels of retinol and therefore fasting is not necessary before a test
...

Serum Retinyl Ester
Less than 5% of vitamin A in the serum is in the form of retinyl esters
...
Because ingestion of
vitamin A immediately preceding a test can cause levels of these esters to rise, a patient
must fast prior to being tested
...
Serum carotenoid levels may be useful
as a secondary measure of vitamin A in populations that consume carotenoids as their
primary vitamin A source, but not very useful for populations consuming primarily
preformed vitamin A
...
In vitamin A deficiency, retinol-binding protein accumulates in the liver as apoRBP, a form that is not bound to retinol
...
Plasma is taken at baseline, a dose of vitamin A is given, and a plasma
sample is taken 5 hours later
...

A percent- change of 20% and higher indicates a deficient liver store of vitamin A
...

Cells are transferred from the conjunctiva to filter paper, where they are stained and
examined under a microscope
...
This
refers to the peak wavelength sensitivity of the retina shifting from red to the blue end of
the spectrum during the transition from day vision to night vision
...


Vitamin C
Vitamin C describes all compounds exhibiting the biological activity of ascorbic acid
...

Plasma Ascorbic Acid
Plasma levels of ascorbic acid are highly influenced by recent dietary intake of vitamin C
at the time of the test
...
2 to 1
...
Normal plasma ascorbic acid is in the range of 0
...
5 mg/dL (2384 mcmol/L)
...
2 and 0
...
423 mcmol/L) and deficiency occurs when below 0
...

Factors that may affect ascorbic acid levels include acute stress due to hot or cold
temperatures, surgery, trauma, infections, inflammatory diseases, the use of oral
contraceptive pills, or cigarette smoking
...

Leukocyte Ascorbic Acid
Leukocyte ascorbic acid tests are more reliable for assessing tissue storage and body
stores, because changes in leukocyte levels are less likely to fluctuate with recent intake
...

Urinary Excretion
Urinary excretion does not parallel vitamin C intake because the kidney is efficient at
reabsorption when intakes are low and at clearance when intakes are high
...
When intake is less than 40 mg/day
urinary excretion falls to less than 10 mg/day and with severe depletion levels are
undetectable
...


Body Size Pool
Isotope dilution can be a reliable method of assessing vitamin-C status
...


Vitamin D

Vitamin D is produced in the skin when exposed to radiation from the sun
...
It is again hydroxylated in the kidney
to 1, 25 dihydroxyvitamin D
...

Serum 25-Hydroxyvitamin D
The vitamin-D metabolite 25-hydroxyvitamin D (25-OH-D) can be measured in the serum
as an indication of liver stores
...
The half-life of 25-OH-D is three weeks; serum levels can reflect vitamin
D from diet and sunlight production over a period of several weeks to several months
...
Values below
10 ng/mL (25 nmol/L) are considered to indicate vitamin-D deficiency
...

Serum vitamin-D levels may increase in summer (with increased exposure to sun), and
may decrease with old age, or as a result of malabsorption diseases
...
The assay provides a direct measure of the biological activity of
1,25 OH2D
...

Serum Alkaline Phosphatase Activity
This functional measure of vitamin D is an indirect measure of vitamin-D status
...


Urinary Calcium Excretion
Measurement of 24-hour urinary calcium excretion can be used as an estimate of
calcium absorption, but is not a very specific test of vitamin-D status
...

Alpha tocopherol is the most abundant form of vitamin E in the body
...
The ratio of tocopherol to lipid provides
a better estimate of vitamin-E status than tocopherol alone
...
8 mg total tocopherol per gram of total lipids
...
Hemolysis of over 10% is associated with
vitamin-E deficiency, though it is not clear whether the assay is indicative of alphatocopherol body stores or blood stores only
...
A negative correlation has been found in children
between plasma vitamin-E levels and breath pentane
...


Clinical Nutritional Assessment

Dietitians have traditionally been involved in the care of hospitalized patients
...
It has been noted that up to 50% of

hospitalized patients are malnourished
...
2 g/dL
...

Nutritional assessment begins with a detailed nutritional history that includes clinical,
dietary, socioeconomic, and family issues
...

Clinicians sometimes use standardized protocols in their assessments
...
This includes the parameters:
serum folate, serum vitamin C, triceps skinfold thickness, serum albumin, absolute
lymphocyte count, hematocrit, mid-arm muscle circumference, and body weight
...
The Prognostic Nutritional
Index (PNI) incorporates serum albumin, serum transferrin, delayed skin hypersensitivity,
and triceps skinfold thickness
...

Functional assessment can also be used to help assess nutritional status
...




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