Lecture 19 - Principles of Biochemical Assessment Flashcards
forms of nutritional assessment
- anthropometric assessment
- dietary assessment
- biochemical assessment
- clinical assessment
what is subclinical mean
before you get any clinical signs
two laboratory methods of biochemical assessment to detect subclinical deficiency and confirm clinical diagnosis
- static biochemical tests
- functional tests
what are two static biochemical tests
- nutrient in biological fluids or tissues (e.g plasma zinc)
- urinary excretion rate of nutrient or metabolites (e.g 24 hour urinary iodine)
what are two functional tests of biochemical assessment
- functional biochemical tests (e.g glutathione peroxidase activity)
- functional physiological or behavioural tests (e.g taste acuity for zinc)
glutathione peroxidase activity is a measure of and how does it work
selenium status,
this works as selenium is a critical component of GP, can look at the rate that GP is able to neutralise a peroxide (as GP is an antioxidant)
what is the definition of precision in biochemical assessment
the degree to which repeated measurements of the same biomarker give the same value
what is precision in biochemical assessment similar to in dietary assessment
similar to repeatability
how to measure precision in biochemical assessment
repeated measures on pooled sample(s) > Coefficient of Variation (CV)
- within run and between run CVs
what is meant by within run and between run CVs when measuring precision in biochemical assessment
within run is within that time you measure and between runs is if you come back and measure the same thing and compare Coefficient of Variation
what is analytical accuracy in biochemical assessment
the difference between the reported and the true amount of the nutrient/metabolite present in the sample is a measure of the analytical accuracy (“trueness”) of the laboratory test
ways of measuring analytical accuracy in biochemical assessment
- recovery test on spiked samples
- certified reference materials
- analysis of pooled sample by multiple labs using different methods
what is an example of certified reference materials for analytical accuracy
human hair = dried powdered hair with a certain amount of zinc in it
you would check if your assay was giving you the right amount
what is analytical sensitivity in biochemical assessment
the smallest concentration that can be distinguished from the blank
was is the limit in analytic sensitivity
~ minimum detection limit
values less than the minimum detection limit should not be recorded
what is analytical specificity in biochemical assessment
the ability of an analytical method to measure exclusively the substance of interest
how can analytical specificity be enhanced
by dry ashing or wet digestion
what is dry ashing and what is it used for
dry ashing is burning the sample
used to enhance analytical specificity
what is wet digestion and what is it used for
breaking down all the other organic material
used to enhance analytical specificity
what is validity in biochemical assessment
how well the biomarker correctly describes the nutritional parameter of interest.
what is an example of validity in biochemical assessment
if the biomarker selected reflects recent dietary exposure, but the study objective is to assess the total body store of a nutrient, the biomarker is said to be invalid
what are key aspects of validity in biochemical assessment
- the assay must be appropriate for the study objective
- drugs, hormones, infection may alter laboratory test results but not actual status
what is sensitivity
how good your method is at identifying people who are a concern = like those who had low intakes
what is specificity
how well does the method identify people who are fine
what is the positive predictive value
if positive result of the test, what is the chance that the test is correct
what is the negative predictive value
if negative result of the test, what is the chance that the negative result is correct
what is venous vs capillary
venous is from the vein
capillary is from the capillary
how to get capillary blood
heel or finger prick
why is capillary blood not always identical to venous blood
can be due to a number of things, not uncommon to milk the sample
what does milk the sample mean (capillary blood)
tiny bead of blood from finger prick so try to squeeze some more our, this means you get some extracellular fluid coming out with the blood which can dilute it (haemodilution)
red top blood collection tubes …. and this is often used to measure
the blood clots when it enters
often used when measuring serum ferritin levels
most of the blood collecting tubes in NZ are
vacutainers (they have a vacuum in them, supports the blood to fill the tube)
lavender / purple top blood collection tubes have …… what would they often be used for
has EDTA (anticoagulant) added to it, so the blood doesn’t clot
often used for whole blood count
what are the fancy / gold top blood collection tubes …. and what tubes would they replace
have gel at the bottom, clot activator and gel separator, has powder that encourages clotting
would replace rep top
what are dark blue/black top blood collection tubes
and what are they important for
trace element free tube, also prevents clotting
zinc is everywhere so it is super easy to contaminate samples, these are important when measuring zinc
what happens to the blood in a purple top
the platelets have been stopped from clotting
what are the key steps in data collection when measuring serum zinc concentration to assess population zinc status
- age
- sex
- time of day
- time since last meal
- presence of symptoms of infections
- other contributing factors such as oral contraception
when collecting zinc blood samples what is important
draw blood using stainless steel needle and collect into trace element free evacuated blood collection tubes
is plasma and serum often separated in zinc blood samples
yes
analytical accuracy is ideally determined using
certified reference materials
venous and capillary blood do not
give the same results
what is serum
Serum is the liquid that remains after the blood has clotted
what is plasma
Plasma is the liquid that remains when clotting is prevented with the addition of an anticoagulant
