Assessment of Protein Status

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

2. 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

3. 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

4. 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.”

5. 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

7. Table 7.6Guidelines for Interpreting Percentile Values for Arm Muscle Area (appendix R)

8. 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

9. Serum Albumin • Major serum protein • Synthesized in liver • Maintains serum osmolarity • Serum carrier of small molecues • Most common indicator of depleted protein status

10. 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

11. 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)

12. 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.

13. 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

14. 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

15. 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

16. 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)

17. 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

18. Total Lympocyte Count • Normal = 1200-1800 cells/mm3 • Moderate PCM = 800-1200 • Severe PCM = < 800

19. 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

20. 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%

21. 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