Assessment of Protein Status

FCSN 442 - Nutrition Assessment LaboratoryDr. 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 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

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)

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.

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

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 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

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)

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 = 800-1200Severe PCM = < 800

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

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%

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