Week 11 Flashcards
(21 cards)
WEEK 11
Introduction to Biochemical Assessment and Protein Status
Intro to biochemical assessment:
2 main types of biochemical tests
1
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2
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1 Static tests
- Measure a nutrient or its metabolites in blood, urine or other body tissues
- Reflect either the total body content of the nutrient, or the size of the tissue store that is most sensitive to depletion
- ____________
2 Functional Tests
- Measure outcomes of nutrient deficiency (or excess)
- Have a greater biological significance than the static tests
EX: immunity status is an indirect measure of protein status
** other examples of functional tests - SLIDE 5 **
- technical, biological and other factors which may confound the interpretation of static and functional tests - slide 6 - look over *
Accuracy in Biochemical Tests
(Analytical Accuracy)
- Has to do with the quality of the biochemical lab technique used
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(standards of known concentration (known “control specimens”) are used to determine accuracy)
- When a measurement is accurate, there is little to no difference between the true and the reported (measured) concentration
Sensitivity in Biochemical Tests
(Analytical Sensitivity)
- Sensitive measures are able to…
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[Assessment indices that show large changes as a result of only small changes in nutrition status have good sensitivity]
- EXAMPLE - slide 9 - READ *
- … detect small changes in nutrition status
- the smallest concentration that can be distinguished from the blank is termed the “analytical sensitivity” or the “minimum detection limit”
- the blank should have the same matrix as the test sample; should contain all the reagents but none of the added analyte/nutrient
- the analytical sensitivity of a biochemical test is particularly important when the nutrient is present in very low concentrations (ie. Cr, Mn)
Specificity in Biochemical Tests
(Analytical Specificity)
- The ability of an analytical test to…
- Assessment indices with good specificity assess…
- EXAMPLE - slide 11 - READ *
- … measure exclusively the substance of interest is referred to as the “analytical specificity”
- … assess only the nutrient of interest
- the test is not affected by differences in metabolism, hormone levels, physical activity etc.
Protein Status
Where is Protein found in the body?
1 -
2 -
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The skeletal muscle protein and the
visceral protein pool = metabolically
available protein
- Protein content of adult body tissues - slide 15 - review *
1 Somatic Protein
- this is skeletal muscle
2 Visceral Protein
- this includes protein found in solid tissue organs (liver, kidneys, pancreas and heart), blood cells (erythrocytes, lymphocytes), as well as serum proteins like albumin
- protein in skin and connective tissue
Nitrogen Balance
In N balance:
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[Nitrogen balance provides no
information on the size of the
protein stores or about the
nutritional status]
Protein (AA) turnover & N balance
–> Protein anabolism
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–> Protein Catabolism
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- N consumed is equal to N excreted
- Protein anabolism is equal to protein catabolism
–> Ana
- AA are used for synthesizing proteins
(are obtained by degrading other proteins)
- AA are also a source of N for other biomolecules
–> Cata
surplus AA are used for fuel
- Carbon skeleton is converted to
(acetyl-CoA / Acetoacetyl - CoA / Pyruvate / citric acid cycle intermediate)
- The Amino group N is converted to and excreted as urea
- Glucose, fatty acids and ketone bodies can be formed from AA
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NEED a 24-hr measurement of protein intake and an estimate of N losses
(EQN - slide 20 ** review)
UUN =
** EXAMPLE - slide 21 - do this! **
+
- Anabolism is higher than catabolism
- Happens during childhood or recovery from trauma or illness; happens during high-intensity resistance training sessions
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- Catabolism is higher than anabolism
- occurs due to conditions of physiological stress, __________
= urine urea N, accounts for about 85-90% of N in the urine
Nitrogen Balance Con’d
Limitations:
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- WHY?
Use of N balance:
- Used most often in research
- May be used in clinical practice, particularly in pts with suspected high protein needs
- Accurate measures of protein intake and 24 hour urinary excretion are difficult to obtain
- The constant of 4 g of N may not be accurate, esp for pts with burns, diarrhea, vomiting or fistulas
- The N balance results tend to be biased toward a positive balance - Why? (intakes of Pro tend to be overestimated, particularly in those with low protein intakes) (excretion tends to be underestimated because of unmeasured N losses)
SOMATIC PROTEIN
Urinary Creatinine Excretion
- Creatinine is…
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Creatine degradation SLIDE 27
Ways to assess urinary creatinine excretion:
- Use the guideline of 23 mg/kg IBW for men and 18 mg/kg IBW for women (expected)
– Use the _____________
** EQN slide 28 **
Interpreting CHI
[ 60-80%: mild protein depletion
40-59%: moderate protein depletion
<40%: severe protein depletion ]
** DO EXAMPLE slide 32 **
- … a product of the breakdown of creatine phosphate in muscle
- Creatinine is cleared and excreted in the urine
(24 hr urinary creatinine excretion gives an estimate of the creatine pool, which is proportional to total muscle mass)
WEEK 11
CON’D
URINARY CREATINE EXCRETION con’d
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( )
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- Most creatine (98%) is in skeletal muscle
- Diet is creatine-free (no meat)
- Total creatine pool and avg concentration of creatine per kg of muscle are constant
- Creatine is converted to creatinine at a constant daily rate
- Creatine is excreted at a constant rate by the kidneys
L
- Obtaining a complete 24 hr urine sample is difficult
(an error as small as 15 min in a collection period -> an error of 1% in the determination of 24 hour urinary creatinine excretion)
- Creatinine derived from dietary sources of creatine can not be distinguished from that derived from endogenously produced creatine
URINARY CREATINE EXCRETION con’d
Specificity - Urinary creatinine can be affected by many factors:
- Increased by:
- Decreased by:
- : meat intake, sepsis, trauma, fever, strenuous exercise, and second half of the menstrual cycle
- : poor renal function, low urine output, aging, muscle atrophy unrelated to nutrition
VISCERAL PROTEIN
- _____ reflect visceral protein status
- The main/major site for the synthesis of visceral proteins is ____
( )
( )
- In acute illness or trauma, levels of some hepatic proteins ______
Positive acute phase proteins (levels _____)
- Ex’s
Negative acute phase proteins (levels _____)
- Ex’s
- ___ serum proteins____ reflect
- is ___ the liver ____
(also called hepatic protein)
(the liver is one of the first organs to be affected by a restricted intake of dietary proteins) - ___increase while others decrease____
+ (levels increase)
Ex’s - C-reactive protein, fibronectin, ferritin
- (levels decrease)
Ex’s - albumin, prealbumin, transferrin, insulin-like growth factor I
- C-reactive protein is the most commonly used indicator
(to see if body is under stress)
VISCERAL PROTEIN Con’d
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- The lower the half-life of the serum protein - the higher the sens to detect changes in protein status (short half-life = faster recycling process & therefore reflect body changes to nutr status much quicker - before too late)
- Half-life is the time it takes before half of the protein is eliminated or broken down
Spec
- Serum proteins tend to have low specificity b/c they can be affected by many factors besides nutrition
ALBUMIN
- Albumin is the most…
- Albumin is a…
- About 60% of albumin is found…
[ ]
(Serum albumin reflects…. )
During chronic malnutrition, concentrations of serum albumin may be maintained by 2 compensatory mechanisms:
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2
[Hypoalbuminaemia = plasma conc of albumin < 40 g/L ]
- … abundant serum protein (makes up about 50-60% of total serum protein)
- … transport protein, and it helps maintain vascular fluid and electrolyte balance
- … in extravascular space, and 40% in intravascular space [intravas - is able to maintain fluid balance - therefore measuring serum albumin = intravascular concentration - telling us about albumin levels]
(… only intravascular levels)
1 Reduction in albumin catabolism
2 Redistribution of extravascular albumin to the intravascular space
Albumin Con’d
In acute illness or trauma:
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VISUAL - slide 46
- Albumin synthesis decreases in the liver
- intravascular albumin levels decrease
(oncotic pressure decreases) - fluid shifts from intravascular to extravascular space, potentially causing edema and ascites
- Albumin synthesis decreases in the liver due to little to no protein intake
- Similar to acute illness or trauma, albumin levels decrease in circulation leading to decreased intravascular oncotic pressure
- This leads to the movement of fluid from intra to extravascular space -> edema, ascites
Albumin Con’d
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Use of Serum Albumin
Serum albumin is frequently used in hospital settings
-May or may not be indicative of protein status
- 50% of patients with PEM had normal serum albumin concentrations
- Low albumin is associated with increased morbidity, mortality and length of stay - so we still measure/keep an eye on it
- Relatively long half-life (17-21 days) therefore, not very sensitive to short-term changes in protein status
- Negative acute phase protein
- Levels of albumin decrease with zinc deficiency, and can be affected by influencing factors other than protein status (renal and liver disease, trauma, surgery, sepsis, burns, hydration status etc.)
( )
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[
- Intravascular transport protein for iron
( Each molecule of transferrin binds with 2 molecules of iron) - 8-10 day half life (more sensitive than albumin)
- Negative acute phase protein
- Levels increase when iron stores decrease (iron deficiency state) (greater need for iron transport)
[- less iron in body = more transferrin produced — PEM + iron deficiency (present at same time) = masks presence of PEM (transferrin should go down with ONLY PEM).. cause transferrin increases production to get more iron in circulation]
AKA [ If PEM is simultaneously present with iron deficiency, a decrease in transferrin concentrations may be masked by an increased caused by iron deficiency]
Sensitivity
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Can be used in hospital setting as a screening tool to identify patients at risk for PEM *
- Summary of Lab protein markers - slide 51 - view *
- READ about CRP - what does it do? *
- Intravascular transport protein for thyroxine and retinol binding protein
- 2 day half-life and small body pool (more sensitive than albumin or transferrin)
- Responds rapidly to changes in protein intake
Spec
- Negative acute phase protein
Sensitivity
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** Understand above - Q on exam **
SUGGESTS using albumin with other markers (in combination) & address any inflammation from baseline ***
Albumin is easy and affordable to use as a measurement
- Intravascular transport protein for retinol
Sens
- 12 hour half life
( - falls rapidly in response to protein deficiency
- falls less rapidly in response to energy deficiency
- responds rapidly to improved protein and energy status)
Spec
- Negative acute phase protein
- Levels decrease with Vit A and zinc deficiency
(note that Vit A and zince deficiency do not affect the levels of transthyretin)
Use of visceral protein biochemistry
- Albumin is commonly used
- Other tests used in pts where protein adequacy needs to be followed closely
Always make sure to check the state of stress/inflammation of the patient
(these lab markers are not reliable by themselves - should only be used as a complement to findings from through examination)
Immunological Tests
VISUAL slide 58
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- Clinical Case - slide 60 *
[ CRP first // Albumin is good to compare to first admitted to hospital and now // Pre-albumin is good for multiple times but costly - and good to do before he leaves & good sensitivity & least to be impacted by specificity (vitamin intakes) as long as inflam has resolved
[Retinol binding protein - VERY sensitive - my not be good cause it can reflect only 1 day of good protein intakes & vit A//zinc deficiency]
SUMMARY of markers - slide 61
- Routinely measured as part of a complete blood count
- Lymphocytes usually make up 20-40% of the total white blood cells
- Low sensitivity and specificity
( - doesn’t provide info on which specific lymphocyte subpopulation is responsible for the lowered count - In addition to PEM, can be influenced by certain micronutrient deficiencies, infections, illnesses, major burns, meds, surgery, stress, general anesthesia, and others )
