Biochemical Assessment

• Biochemical measurements


  Estimation of tissue desaturation, enzyme activity or blood composition. Tests are confined to two easily obtainable fluids namely blood and urine and results are generally compared to standards.

  
• Advantages of biochemical measurements

  • Objectivity
  • Can detect early subclinical states of nutritional deficiency
• Disadvantages of biochemical measurements

  • Costly, usually requiring expensive equipments
  • Time consuming
  • Difficult to collect samples
  • Lack of practical standards of sample collection
• Factors affecting accuracy of results


  • Method of sample collection
  • Method of transport and storage of samples
  • Technique employed
• Ideal biochemical tests


  • Specific
  • Simple
  • Inexpensive
  • Reveal tissue depletion at an early stage
  • Require less sophisticated equipment and skill
• Static biochemical tests


  Involve measurement of levels of a nutrient or a metabolite in a preselected biopsy material that reflects either the total body content of the nutrient or the size of the tissue store most sensitive to depletions
• Categories of static biochemical tests

  • Measurement of a nutrient in biological fluids or tissues
  • Measurement of the urinary excretion rate of the nutrient
• Static biochemical tests


  • Reflect recent dietary intake or acute status
  • Urine cannot be used to assess vitamins A, D, E and K as metabolites are not excreted in proportion to the amount of these vitamins consumed, absorbed, and metabolized
  • Can be used for assessment of some minerals, water-soluble B-complex vitamins, vitamin C, and protein
• Functional tests


  • Diagnostic tests to determine the sufficiency of host nutritive to permit cells, tissues, organs, anatomical systems, or the host to perform optimally the intended, nutrient-dependent biological function
  • Indicates severity of deficiency; measures the effect of lack thereof on the enzymes by which the body makes use of its nutrient intake
• Categories of functional tests

  • Enzymatic tests which measures the activity of an enzyme which requires the vitamin as a coenzyme added in vitro
  • Metabolic tests which measures the rise in concentration of metabolite in blood or urine after administering a load of an appropriate precursor
• Assessment of performance of laboratory tests

  • Accuracy
  • Precision
  • Within assay variability
  • Between assay variability
• Protein status


  Evaluated by assessing both somatic and visceral protein status. Somatic protein status can generally be performed using muscle circumference or mid-arm muscle area. Biochemical measures can help better provide perspective for somatic protein status.
• Functions of protein


  • Protein is the body's building block. All of our organs, including the skin, are built from proteins, as are the muscles, hair and nails. Proteins are responsible for nearly every task of cellular life, including cell shape and inner organization, product manufacture and waste cleanup, and routine maintenance. Proteins also receive signals from outside the cell and mobilize intracellular response.
• Indices of protein status

  • Laboratory indices of protein status measure somatic protein status, visceral protein status, metabolic changes, muscle function and immune function.
• Urinary creatine excretion


  Creatinine is a chemical waste product in the blood that passes through the kidneys to be filtered and eliminated in urine. Creatinine is made from creatine, a supplier of energy to the muscle. Urinary creatinine is used to assess the degree of depletion of muscle mass in marasmic patients, and degree of repletion after long term intervention, provided that 72-hour urine collections are made.
• Creatinine levels


  • Women: 0.5 to 1.1 mg/dL
  • Men: 0.6 to 1.2 mg/dL
• Creatinine height index guidelines

  • Less than acceptable: <0.5
  • Acceptable (low risk): 0.5 - 0.9
  • Deficient (high risk): >0.9
• Factors affecting daily creatinine excretion

  • Diurnal and day to day variations
  • Strenuous exercise
  • Emotional stress
  • Dietary intakes of creatinine and creatinine
  • Menstruation
  • Age
  • Infection, fever, and trauma
  • Chronic renal failure
• 1. Methylhistidine excretion


  An amino acid present almost exclusively in the actin of all skeletal muscle fibers and the myosin of white fiber; a marker of muscle protein that is not widely used.
• Serum proteins


  An index of visceral protein status; easily measured but rather insensitive index of protein status.
• Interpretative guidelines for serum protein concentrations

  • Infants 0 to 11 months: Less than acceptable: -, Acceptable (low risk): <5.0, Deficient (high risk): ≥5.0
  • Children 1 to 5 years: Less than acceptable: -, Acceptable (low risk): <5.5, Deficient (high risk): ≥5.5
  • Children 6 to 17 years old: Less than acceptable: -, Acceptable (low risk): <6.0, Deficient (high risk): ≥6.0
  • Adult: Less than acceptable: <6.0, Acceptable (low risk): 6.0 to 6.4, Deficient (high risk): ≥6.5
  • Pregnant, 2nd and 3rd trimester: Less than acceptable: <5.5, Acceptable (low risk): 5.5 to 5.9, Deficient (high risk): ≥6.0
• Serum albumin


  Reflects changes occurring within intravascular space and not the total visceral protein pool; not very sensitive to short-term changes in protein status; has long half-life of 14 to 20 days.
• Interpretative guidelines for serum albumin concentrations

  • Infants 0 to 11 months: Less than acceptable: -, Acceptable (low risk): <2.5, Deficient (high risk): ≥2.5
  • Children 1 to 5 years: Less than acceptable: <2.8, Acceptable (low risk): <3.0, Deficient (high risk): ≥3.0
  • Children 6 to 17 years old: Less than acceptable: <2.8, Acceptable (low risk): <3.5, Deficient (high risk): ≥3.5
  • Adults: Less than acceptable: <2.8, Acceptable (low risk): 2.8 to 3.4, Deficient (high risk): ≥3.5
  • Pregnant 1st trimester: Less than acceptable: <3.0, Acceptable (low risk): 3.0 to 3.9, Deficient (high risk): ≥4.0
  • Pregnant, 2nd and 3rd trimester: Less than acceptable: <3.0, Acceptable (low risk): 3.0 to 3.4, Deficient (high risk): ≥3.5
• Serum transferrin


  Transferrin is a serum beta-globulin protein synthesized primarily in the liver and is located almost totally intravascularly; serves as the iron transport protein and is a bacteriostatic (it binds with free iron and prevents the growth of gram negative bacteria which require iron for growth).
• Interpretative guidelines for serum transferrin

  • Protein Deficit: None: >200, Mild: 150-200, Moderate: 100-150, Severe: <100
• Serum retinol-binding protein


  RBP is the carrier protein for retinal; serum RBP concentrations tend to fall rapidly in response to protein and to energy deprivation and respond quickly to dietary treatment. They are carrier proteins that bind retinol. Assessment of retinol-binding protein is used to determine visceral protein mass in health-related nutritional studies.
• Interpretative guidelines for retinol-binding protein

  • Protein Deficit: None: 2.6-7.6 mg/dl, Mild: -, Moderate: -, Severe: -
• Serum thyroxine-binding pre-albumin


  TBPA serves as transport protein for thyroxine and as a carrier protein for RBP. More sensitive index of protein status and responds more rapidly to dietary treatment.
• Interpretative guidelines for thyroxine-binding pre-albumin

  • Protein Deficit: None: 15.7-29.6 mg/dl, Mild: 10-15 mg/dl, Moderate: 5-10 mg/dl, Severe: <5 mg/dl
• Serum somatomedin-C


  Somatomedins are growth hormone dependent serum growth factors produced by the liver. They circulate bound to carrier proteins and have a half-life for several hours. More sensitive to acute changes in protein status than the other serum proteins.
• Serum amino-acid ratio


  Children with kwashiorkor generally have serum NEAA:EAA ratios above 3; whereas for normal children and those with marasmus, ratios are usually less than 2.
• Guidelines for the interpretation of serum nonessential: essential amino acid ratio

  • Less than acceptable: >3.0, Acceptable (low risk): 2.0-3.0, Deficient (high risk): <2.0
• Urinary 3-hydroxyproline excretion


  Urinary 3-hydroxyproline is an excretory product derived from the soluble and insoluble collagens of both soft and calcified tissues.
• Hydroxyproline: creatinine ratio


  Corrects for difference in adult body size. Calculated as mg hydroxyproline per 24 hour / mg creatinine per 24 hours.
• Hydroxyproline index


  Calculated as mg hydroxyproline per ml urine x kg body weight / mg creatinine per ml urine.
• Guidelines for the interpretation of urinary hydroxyproline index

  • Less than acceptable: <1.0, Acceptable (low risk): 1.0-2.0, Deficient (high risk): >2.0
• Nitrogen balance


  A measure of net changes in total body protein mass. Sources of nitrogen intake include meat, dairy, eggs, nuts and legumes, and grains and cereals. Examples of nitrogen losses include urine, feces, sweat, hair, and skin. Blood urea nitrogen can be used in estimating nitrogen balance, as can the urea concentration in urine.
• Urinary urea nitrogen: creatinine ratios


  Urea is the largest source of urinary nitrogen and is synthesized in the liver. Urinary urea nitrogen: creatinine ratios are used as an index of dietary protein intake but not an index of long-term protein status.
• Guidelines for the interpretation of urinary urea nitrogen: creatinine ratios

  • Less than acceptable: <6.0, Acceptable (low risk): 6.0-12.0, Deficient (high risk): >12.0
• Functional tests of protein status

  Include muscle function and immunological tests. Muscle function measures changes in muscle contractility, relaxation rate, endurance, and hand grip strength. Immunological tests include lymphocyte count, delayed cutaneous hypersensitivity, measurement of thymus-dependent lymphocytes, and lymphocyte nitrogen assays.