Assessment of Nutritional Status - Biochemical Flashcards
What are the two kinds of biochemical test?
static
functional
Describe static tests
Measure of nutrient or metabolite in biological sample e.g.,
- blood
- urine
- serum
- faeces
What is a limitation of static testing?
fail to reflect the overall nutritional status of an individual
e.g.,
blood test may show low Ca level in blood but this does not indicate poor bone health overall
describe functional tests
assessing performance of one or more physiologic functions that rely on a specific nutrient for optimal performance
give an example of a functional test
dark adaptation test for vit A deficiency
What is a limitation of functional tests?
non specific - can identify that there may be a nutrient deficiency but can’t specify which nutrient
list some confounding factors (subject related, method related, sample related and health related) that may influence the result of a biochemical test
- subject related factors e.g., age, sex, ethnicity, weight, diet
- method related factors e.g., precision, accuracy, validity, sensitivity
- sample factors e.g., contamination or haemolysis
- health related factors e.g., disease
what is the difference between test sensitivity and test specificity
test sensitivity
- ability of a test to identify who does have the deficiency
test specificity
- ability of a test to identify who does not have the deficiency
What is positive predictive value?
probability of those with positive result truly have the deficiency
what is negative predictive value?
probability that those who receive a negative result truly don’t have the disease
what are the four stages in the analysis of biopsy material?
sample
storage
prep
analysis
What information can you yield from measuring nutritional biomarkers in biological tissues e.g., blood, urine, muscle?
- can compare nutrient intake with estimated intake from dietary assessment
- validates dietary assessment
- detect pre-clinical disease
- test subject exposure to dietary interventions
what are some factors that can influence blood?
hydration fasting/eating medications infection inflammation
Why is blood a favourable biological sample?
easy to obtain
non-invasive
easy to analyse
why do plasma and serum nutrient levels reflect recent dietary intake?
plasma and serum carry recently absorbed nutrients to body tissues
why would you conduct a fasting blood test?
when you want to look at long-term/chronic deficiency
plasma and serum levels reflect recently absorbed nutrients therefore fasting reduced serum/plasma nutrient levels
what is the difference between serum and plasma?
serum = plasma without the clotting factors (fibrin)
plasma = component of blood in which blood cells are suspended along with proteins and clotting factors
what does the nutrient content of erythrocytes show and why?
chronic nutrient deficiency
lifespan of these cells is long (120 days)
what are the 3 types or urine test?
- fasting
- 24 hour
- 2nd fasted early morning
Why is urine testing favourable?
cheap
non invasive
does urine content reflect acute or chronic nutritional status?
acute
describe a limitation of urinary testing
certain factors e.g., infection, antibiotics, alcoholism can increase nutrient levels in urine so may not accurately reflect nutrient status
list the 6 main serum proteins
serum albumin serum pre-albumin thyroxine binding pre-albumin transferrin retinol binding protein insulin-like growth factor 1 (IGF-1)
Describe Nitrogen-balance as a method of assessing protein status
measurement of nitrogen excretion to monitor changes in total protein mass
what is the equation for nitrogen balance?
how is nitrogen intake calculated?
how is nitrogen loss calculated?
nitrogen balance = nitrogen intake - nitrogen loss
nitrogen intake = protein intake (g) / 6.25
nitrogen loss = urinary urea nitrogen + 4
list some indicators of total body protein status
mid arm muscle circumference
total body potassium level
total body nitrogen level
densitometry
Why is immunocompetence used as a measure of nutritional status?
there is a close relationship between immunity and nutritional status
immunocompetence = early indicator of nutrient deficiency
