Assessment of Protein Status
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Assessment of Protein Status
FCSN 442 - Nutrition Assessment LaboratoryDr. David L. Gee
Central Washington University
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Assessment of Protein Status
Anthropometric Assessment– body composition estimations– midarm muscle circumference/area
Laboratory Assessment – serum albumin– other serum proteins (transferrin, prealbumin,
retinol-binding protein)– urinary creatinine excretion– total lymphocyte count
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Midarm Muscle Area
Estimate of MAMA is an estimate of overall muscle mass– single point vs serial measurements
Assumptions– arm, muscle, bone are circular– TSF is 2X the thickness of fat– bone area is constant
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Midarm Muscle Circumference
MAMC = AC - (.314 x TSF)– MAMC = midarm muscle circumference in cm– AC = arm circumference in cm– TSF = tricep skinfold in mm
“…change in arm muscle area is greater than the change in mid-arm circumference. Consequently, changes in upper-arm musculature are not as easily detected by measurement of mid-arm circumference as by AMA. Therefore, AMA is the preferred nutritional index.”
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Arm Muscle Area
AMA = ((MAC - (3.14 x TSF)2 ) / (4 x 3.14)– AMA = arm muscle area (cm2)– MAC = mid-arm circumference (cm)– TSF = tricep skinfold thickness (cm)
• Or units of AMA, MAC, TSF all in mm• To convert mm2 to cm2, divide mm2/100
adjusted AMA– corrected for “bone free” AMA
• Subtract constant from AMA to account for bone, nervous tissue, vascular tissue.
– p-304
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Table 7.6
Guidelines for Interpreting Percentile Values for Arm Muscle Area (appendix R)
Percentile Category
< 5th pct Wasted
5th -15th pct Below Average
15th - 85th pct Average
85th – 95th pct Above Average
> 95th pct High Muscle
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Biochemical Assessment of Protein Status
Two protein compartment model– Somatic protein (skeletal muscle protein)
• ~75% of total body protein– Visceral protein (internal organs, blood cells, serum proteins)
• ~ 25% of total body protein
“No single test or group of tests can be recommended at this time as a routine and reliable indicator of protein status.” Young, 1990“…a combination of measures can produce a more complete picture of protein status.”– Biochemical, anthropometric, dietary, and clinical findings
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Serum Albumin
Major serum protein– Synthesized in liver– Maintains serum osmolarity– Serum carrier of small molecues
Most common indicator of depleted protein status
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Serum AlbuminHalf life = 14-20 days– large body pool
poor indicator of early protein depletion and repletionLevels affected by rate of synthesis (liver disease may reduce levels)
May reflect level of physiological stress– Decreased during acute catabolic phase
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Serum AlbuminLevels affected by abnormal losses– thermal burns – losses at burn site– nephrotic syndrome – losses in urine– protein-losing enteropathies – losses in feces
Levels affected by fluid status– congestive heart disease & fluid overload
• Reduced due to dilution– Dehydration
• Increased due to concentration effects
Normal values: 4.5 g/dL + 35-50 (SD)
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Serum Transferrin
Function: transport protein for ironhalf-life = 8-9 days– better index of changes of protein status
Influenced by other factors– Increased with iron deficiency– increased during pregnancy, estrogen therapy– reduced in protein-losing enteropathy, nephropathy, acute
catabolic stresslimited usefulness in protein status assess.
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Serum Prealbumin
aka. transthyretin and thyroxine-binding prealbuminfunctions:– transport protein for thyroxine– carrier protein for retinol binding protein
short half life (2-3d), small body pool– sensitive indicator of protein status– responds more rapidly than albumin or transferrin
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Serum Prealbumin
Returns to normal at beginning of nutritional therapy– therefore do not use as endpoint for terminating
nutritional therapy
Influenced by other factors– increased in chronic renal failure on dialysis– reduced in acute catabolic states, post surgery, tissue
trauma, sepsis
generally considered preferable than albumin and transferrin
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Retinol Binding Protein
Function: carrier for retinol– complexes with prealbumin (1:1)
responds like prealbuminvery rapid turnover (12 hours), very small body pool– may be too sensitive and complicates precise
measurements
generally not considered to be more useful than prealbumin
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Immunocompetence
Immune system affected by nutritional statusTests of immunocompetence useful functional indicators of nutritional statusDelayed Cutaneous Hypersensitivty (DCH)– intradermal injection of antigens
Total Lymphocyte Count (TLC)
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Total Lympocyte Count
White blood cell count– elevated with infections– used with % lymphocyte to get total
lymphocyte count (TLC)
TLC = (%lymp x WBC)x100– ex: TLC=(37.2%x4100)x100 =1525
cells/mm3
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Total Lympocyte Count
Normal = 1200-1800 cells/mm3
Moderate PCM = 800-1200Severe PCM = < 800
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Urinary Creatinine Excretion
Creatinine excreted in proportion to muscle massLBM estimated by comparing 24-hr urine creatinine excretion with standard based on stature or reference values of 23 and 18 mg/kg for M and F
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Example:Joe is 5’10” tall, 178cm70kg
24hr creatinine excretion =1436 mg
Expected creatinine @23mg/kg= 23 x 70 = 1610 mg
% expected = 1436/1610 x 100= 89%
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Creatinine Height Index
CHI = (24 hr urine creatinine x 100) / (expected 24 hr urine creatinine for height)– CHI = 1436/1596 x 100 = 90%
expected values in table 9-1 (p306)– CHI > 80% = normal– CHI = 60-80% = mild protein depletion– CHI = 40-60% = moderate depletion– CHI < 40% = severe depletion