123 biochemical assessment

• Generalized Scheme for the Development of a Nutritional Deficiency

  
  

  1. Dietary inadequacy
  2. Decreased level in reserve tissue store
  3. Decreased level in body fluids
  4. Decreased functional level in tissues
  5. Decreased activity of nutrient-dependent enzyme or mRNA for some proteins
  6. Functional changes
  7. Clinical signs/symptoms
  8. Anatomical signs
• biochemical assessment


  “measurement of a nutrient and its metabolite in blood, feces, urine, or blood which has a relationship to nutritional status”
• biochemical assessment


  more objective and precise than other methods
• biochemical assessment


  Can identify borderline nutritional condition prior to appearance of symptoms
• Biochemical Assessment

  Reveal marginal or acute deficiencies when clinical signs are normal since clinical signs usually occur only after prolonged inadequate intakes.
• Objectives of Biochemical Assessment

  detect marginal nutritional deficiencies in individuals particularly when dietary histories are questionable or unavailable
• Objectives of Biochemical Assessment

  supplement or enhance studies such as dietary or community assessment among specific population groups, in order to pinpoint nutritional problems that these modalities may have suggested or failed to reveal.
• Limitations

  May not necessarily reflect presence of pathological lesion nor show health

  significance in relation to nutritional status;
• Limitations

  Affected by biological or technical factors (confounders) rather than

  nutrient status;
• limitations

  May not always reflect total body nutrient content or tissue stores which is

  most sensitive to nutritional change;
• limitations

  Interpretation of results are not always simple.
• Laboratory Methods are Used to Determine Deficiencies in:

  • Serum protein particularly albumin level
  • Blood-forming nutrients – iron, folacin, vitamin B6, and vitamin B12
  • Water-soluble vitamins – thiamine, riboflavin, niacin, and vitamin C
  • Fat-soluble vitamins – A, D, E, K
  • Minerals – iron, iodine and other trace minerals
  • Lipids and glucose – cholesterol, triglycerides, various enzymes which are implicated in heart disease, diabetes, and other chronic diseases
• Types of Biochemical Tests

  static biochemical, functional test
• Types of Functional Tests

  functional biochemical, functional physiological
• Static biochemical tests

  Measure the level of a nutrient or urinary excretion rate or its metabolite
• Static biochemical tests


  Provide information on the degree of deficiency of the particularly body pool

  sampled
• Static biochemical tests

  Useful for identifying the second and third stages in the development of a

  nutritional deficiency
• Static biochemical tests

  change of nutrient concentration in any given specimen which is most sensitive to nutritional change
• Static biochemical tests

  Some static biochemical tests measure levels of the nutrient in biological

  fluids and tissues on the assumption that such tests reflect the total body

  nutrient content or the nutrient tissue store most sensitive to depletion
• Functional tests


  bridge the information gap between an 'abnormal' nutrient concentration and a seriously abnormal metabolic function
• Functional physiological tests

  • assess the physiological performance of an individual in vivo; None of the tests are specific and must be interpreted along with biochemical measurements.

  Determine the changes in the activities of enzymes dependent on a specific nutrient or in the concentrations of specific blood components dependent on a given nutrient.
• Functional biochemical tests


  Assess the consequences of the nutrient deficiency by measuring changes in the activities of a specific enzyme or in the concentrations of specific blood components dependent on a given nutrient
• Potential Confounders


  • Subject characteristics
  • Health condition
  • Biological
  • Sampling errors
• Subject characteristics


  • age
  • sex
  • ethnic/race
  • physiological status
  • hormonal status
  • supplement use
  • genetic
  • physical activity
  • environment
  • recent dietary intake
• Health condition


  • disease
  • infection
  • inflammation
  • stress
  • medication
  • hydration status
  • catabolic state
• Biological


  • homeostatic regulation
  • time variation
  • nutrient interaction
  • fasting or no-fasting
• Sampling errors


  • selection bias during collection procedures
  • including only persons attending under-fives clinic and excluding non-attendees (non-response bias)
  • ignoring people who did not respond in the initial attempt to include them in the study
  • collecting data at one season of the year (seasonal bias)
• Potential Confounders


  5. method: reference data/standards, cut-off values

  6. specimen: contamination or lysis, time of collection,

  7. measurement errors: analytical sensitivity of a biochemical method is important when the nutrient of interest is present in low concentrations,
• analytical specificity


  ability of an analytical method to measure only the substance of interest; specific analytical methods do not generate false-positive results
• Factors to Consider in Specimen Collection

  ease of data/sample collection, sample storage and transport, transportability of field equipment, expertise available for collection and analysis, equipment available and its maintenance, culture and religious context, costs
• Commonly Used Specimen

  • Venous blood – preferred for most hematologic examinations
  • Capillary blood – for infants, very young children, elderly patients with fragile veins, and severely burned patients; used in POC
  • Erythrocyte – nutrient reflects chronic status
  • Leucocyte – reflects acute nutrient status; age and size of the cell determine nutrient content; infection influences nutrient concentration in the cells
• Commonly Used Specimen


  • Breast milk: vitamin A, Se, I

  • Sweat: K

  • Semen: Zn

  • Hair: Zn, Se, Cr, Mn

  • Nails: Se

  • Mucosal swab: lipid, folate, a-tocopherol

  • Stool: fat, Fe

  • Biopsy materials: skin, fat

  • Liver: Fe, vitamin A, Ca

  • Amniotic fluid
• Commonly Used Specimen - Urine


  readily available and non invasive;

  24-hour urine is the most preferred as concentration of nutrient metabolite is not equally distributed throughout the day;

  normal renal function is a prerequisite when used as specimen to

  determine nutritional status;

  Protein, vitamins, sodium, potassium, iodine, selenium, chromium
• Selection of Laboratory Methods for Nutritional Impact Evaluation


  depends on the: nature of the intervention, kind, severity, and prevalence of nutritional problems in the population
• Nutritional biomarkers


  biological characteristics, biological measurements used to indicate normal biological and pathogenic processes

  essential for assessing the nutritional status of an individual and/or population.
• Uses of nutritional biomarkers

  population-level biomarkers for screening, surveillance, and monitoring and evaluation of interventions

  Clinicians use biomarkers mainly for diagnosis, prognosis, and treatment;

  researchers use biomarkers for any or all of these purposes based on

  their needs.
• Classification of nutritional biomarkers


  biomarkers of exposure, biomarkers of status, biomarkers of function
• Biomarkers of “exposure”: Biomarkers of “status”:

  body fluids and tissues
• Biomarkers of “function":


  extent of the functional consequences of a nutrient deficiency; EARLY BIOMARKERS OF SUBCLINICAL DEFICIENCIES
• Biomarkers of “function": functional biochemical


  enzyme stimulation assays; abnormal metabolites; DNA damage