Lecture 19 - Principles of Biochemical Assessment

Question 1

forms of nutritional assessment

Answer 1

• anthropometric assessment
• dietary assessment
• biochemical assessment
• clinical assessment

Question 2

what is subclinical mean

Answer 2

before you get any clinical signs

Question 3

two laboratory methods of biochemical assessment to detect subclinical deficiency and confirm clinical diagnosis

Answer 3

1. static biochemical tests
2. functional tests

Question 4

what are two static biochemical tests

Answer 4

• nutrient in biological fluids or tissues (e.g plasma zinc)
• urinary excretion rate of nutrient or metabolites (e.g 24 hour urinary iodine)

Question 5

what are two functional tests of biochemical assessment

Answer 5

• functional biochemical tests (e.g glutathione peroxidase activity)
• functional physiological or behavioural tests (e.g taste acuity for zinc)

Question 6

glutathione peroxidase activity is a measure of and how does it work

Answer 6

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)

Question 7

what is the definition of precision in biochemical assessment

Answer 7

the degree to which repeated measurements of the same biomarker give the same value

Question 8

what is precision in biochemical assessment similar to in dietary assessment

Answer 8

similar to repeatability

Question 9

how to measure precision in biochemical assessment

Answer 9

repeated measures on pooled sample(s) > Coefficient of Variation (CV)

• within run and between run CVs

Question 10

what is meant by within run and between run CVs when measuring precision in biochemical assessment

Answer 10

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

Question 11

what is analytical accuracy in biochemical assessment

Answer 11

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

Question 12

ways of measuring analytical accuracy in biochemical assessment

Answer 12

• recovery test on spiked samples
• certified reference materials
• analysis of pooled sample by multiple labs using different methods

Question 13

what is an example of certified reference materials for analytical accuracy

Answer 13

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

Question 14

what is analytical sensitivity in biochemical assessment

Answer 14

the smallest concentration that can be distinguished from the blank

Question 15

was is the limit in analytic sensitivity

Answer 15

~ minimum detection limit

values less than the minimum detection limit should not be recorded

Question 16

what is analytical specificity in biochemical assessment

Answer 16

the ability of an analytical method to measure exclusively the substance of interest

Question 17

how can analytical specificity be enhanced

Answer 17

by dry ashing or wet digestion

Question 18

what is dry ashing and what is it used for

Answer 18

dry ashing is burning the sample

used to enhance analytical specificity

Question 19

what is wet digestion and what is it used for

Answer 19

breaking down all the other organic material

used to enhance analytical specificity

Question 20

what is validity in biochemical assessment

Answer 20

how well the biomarker correctly describes the nutritional parameter of interest.

Question 21

what is an example of validity in biochemical assessment

Answer 21

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

Question 22

what are key aspects of validity in biochemical assessment

Answer 22

• the assay must be appropriate for the study objective
• drugs, hormones, infection may alter laboratory test results but not actual status

Question 23

what is sensitivity

Answer 23

how good your method is at identifying people who are a concern = like those who had low intakes

Question 24

what is specificity

Answer 24

how well does the method identify people who are fine

Question 25

what is the positive predictive value

Answer 25

if positive result of the test, what is the chance that the test is correct

Question 26

what is the negative predictive value

Answer 26

if negative result of the test, what is the chance that the negative result is correct

Question 27

what is venous vs capillary

Answer 27

venous is from the vein capillary is from the capillary

Question 28

how to get capillary blood

Answer 28

heel or finger prick

Question 29

why is capillary blood not always identical to venous blood

Answer 29

can be due to a number of things, not uncommon to milk the sample

Question 29

what does milk the sample mean (capillary blood)

Answer 29

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)

Question 30

red top blood collection tubes .... and this is often used to measure

Answer 30

the blood clots when it enters often used when measuring serum ferritin levels

Question 31

most of the blood collecting tubes in NZ are

Answer 31

vacutainers (they have a vacuum in them, supports the blood to fill the tube)

Question 32

lavender / purple top blood collection tubes have ...... what would they often be used for

Answer 32

has EDTA (anticoagulant) added to it, so the blood doesn't clot often used for whole blood count

Question 33

what are the fancy / gold top blood collection tubes .... and what tubes would they replace

Answer 33

have gel at the bottom, clot activator and gel separator, has powder that encourages clotting would replace rep top

Question 34

what are dark blue/black top blood collection tubes and what are they important for

Answer 34

trace element free tube, also prevents clotting zinc is everywhere so it is super easy to contaminate samples, these are important when measuring zinc

Question 35

what happens to the blood in a purple top

Answer 35

the platelets have been stopped from clotting

Question 36

what are the key steps in data collection when measuring serum zinc concentration to assess population zinc status

Answer 36

- age - sex - time of day - time since last meal - presence of symptoms of infections - other contributing factors such as oral contraception

Question 37

when collecting zinc blood samples what is important

Answer 37

draw blood using stainless steel needle and collect into trace element free evacuated blood collection tubes

Question 38

is plasma and serum often separated in zinc blood samples

Answer 38

yes

Question 39

analytical accuracy is ideally determined using

Answer 39

certified reference materials

Question 40

venous and capillary blood do not

Answer 40

give the same results

Question 41

what is serum

Answer 41

Serum is the liquid that remains after the blood has clotted

Question 42

what is plasma

Answer 42

Plasma is the liquid that remains when clotting is prevented with the addition of an anticoagulant