Assessment of Protein Status

Assessment of Protein Status
FCSN 442 - Nutrition Assessment Laboratory
By:Dr. David L. Gee
Central Washington University

Assessment of Protein Status
* Anthropometric Assessment
o body composition estimations
o midarm muscle circumference/area
* Laboratory Assessment
o serum albumin
o other serum proteins (transferrin, prealbumin, retinol-binding protein)
o urinary creatinine excretion
o total lymphocyte count

Midarm Muscle Area
* Estimate of MAMA is an estimate of overall muscle mass
* Assumptions

Midarm Muscle Circumference
* MAMC = AC - (.314 x TSF)

* “…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)
* adjusted AMA

Guidelines for Interpreting Percentile Values for Arm Muscle Area (appendix R)
Biochemical Assessment of Protein Status
* Two protein compartment model
* “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.”

Serum Albumin
* Major serum protein
* Most common indicator of depleted protein status
* Half life = 14-20 days
* 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
* Levels affected by abnormal losses
* Levels affected by fluid status
* Normal values: 4.5 g/dL + 35-50 (SD)

Serum Transferrin
* Function: transport protein for iron
* half-life = 8-9 days
* Influenced by other factors
* limited usefulness in protein status assess.

Serum Prealbumin
* aka. transthyretin and thyroxine-binding prealbumin
* functions:
* short half life (2-3d), small body pool
* Returns to normal at beginning of nutritional therapy
* Influenced by other factors
* generally considered preferable than albumin and transferrin

Retinol Binding Protein
* Function: carrier for retinol
* responds like prealbumin
* very rapid turnover (12 hours), very small body pool
* 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)
o intradermal injection of antigens
* Total Lymphocyte Count (TLC)

Total Lympocyte Count
* White blood cell count
* TLC = (%lymp x WBC)x100
* 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: Creatinine Height Index * CHI = (24 hr urine creatinine x 100) / (expected 24 hr urine creatinine for height) o CHI = 1436/1596 x 100 = 90% * expected values in table 9-1 (p306) o CHI > 80% = normal
o CHI = 60-80% = mild protein depletion
o CHI = 40-60% = moderate depletion
o CHI < 40% = severe depletion Assessment of Protein Status