Assessment of Protein Status
FCSN 442 - Nutrition Assessment Laboratory
Dr. David L. Gee
Central Washington University
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
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
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.”
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
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
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
Serum Albumin
Major serum protein
– Synthesized in liver
– Maintains serum osmolarity
– Serum carrier of small molecues
Most common indicator of
depleted protein status
Serum Albumin
Half life = 14-20 days
– large body pool
poor indicator of early protein
depletion and repletion
Levels affected by rate of synthesis
(liver disease may reduce levels)
May reflect level of physiological
stress
– Decreased during acute catabolic phase
Serum Albumin
Levels 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)
Serum Transferrin
Function: transport protein for iron
half-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 stress
limited usefulness in protein status assess.
Serum Prealbumin
aka. transthyretin and thyroxine-binding
prealbumin
functions:
– 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
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
Retinol Binding Protein
Function: carrier for retinol
– complexes with prealbumin (1:1)
responds like prealbumin
very 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
Immunocompetence
Immune system affected by nutritional
status
Tests of immunocompetence useful
functional indicators of nutritional status
Delayed Cutaneous Hypersensitivty (DCH)
– intradermal injection of antigens
Total Lymphocyte Count (TLC)
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
Total Lympocyte Count
Normal = 1200-1800 cells/mm3
Moderate PCM = 800-1200
Severe PCM = < 800
Urinary Creatinine Excretion
Creatinine excreted in proportion to muscle
mass
LBM 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
Example:
Joe is 5’10” tall, 178cm
70kg
24hr creatinine excretion =
1436 mg
Expected creatinine @23mg/kg
= 23 x 70 = 1610 mg
% expected = 1436/1610 x 100
= 89%
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