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HUNT 242 > Lecture 19 - Principles of Biochemical Assessment > Flashcards

Lecture 19 - Principles of Biochemical Assessment Flashcards

1
Q

forms of nutritional assessment

A
  • anthropometric assessment
  • dietary assessment
  • biochemical assessment
  • clinical assessment
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2
Q

what is subclinical mean

A

before you get any clinical signs

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3
Q

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

A
  1. static biochemical tests
  2. functional tests
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4
Q

what are two static biochemical tests

A
  • nutrient in biological fluids or tissues (e.g plasma zinc)
  • urinary excretion rate of nutrient or metabolites (e.g 24 hour urinary iodine)
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5
Q

what are two functional tests of biochemical assessment

A
  • functional biochemical tests (e.g glutathione peroxidase activity)
  • functional physiological or behavioural tests (e.g taste acuity for zinc)
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6
Q

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

A

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)

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7
Q

what is the definition of precision in biochemical assessment

A

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

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8
Q

what is precision in biochemical assessment similar to in dietary assessment

A

similar to repeatability

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9
Q

how to measure precision in biochemical assessment

A

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

  • within run and between run CVs
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10
Q

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

A

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

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11
Q

what is analytical accuracy in biochemical assessment

A

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

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12
Q

ways of measuring analytical accuracy in biochemical assessment

A
  • recovery test on spiked samples
  • certified reference materials
  • analysis of pooled sample by multiple labs using different methods
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13
Q

what is an example of certified reference materials for analytical accuracy

A

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

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14
Q

what is analytical sensitivity in biochemical assessment

A

the smallest concentration that can be distinguished from the blank

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15
Q

was is the limit in analytic sensitivity

A

~ minimum detection limit

values less than the minimum detection limit should not be recorded

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16
Q

what is analytical specificity in biochemical assessment

A

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

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17
Q

how can analytical specificity be enhanced

A

by dry ashing or wet digestion

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18
Q

what is dry ashing and what is it used for

A

dry ashing is burning the sample

used to enhance analytical specificity

19
Q

what is wet digestion and what is it used for

A

breaking down all the other organic material

used to enhance analytical specificity

20
Q

what is validity in biochemical assessment

A

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

21
Q

what is an example of validity in biochemical assessment

A

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

22
Q

what are key aspects of validity in biochemical assessment

A
  • the assay must be appropriate for the study objective
  • drugs, hormones, infection may alter laboratory test results but not actual status
23
Q

what is sensitivity

A

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

24
Q

what is specificity

A

how well does the method identify people who are fine

25
Q

what is the positive predictive value

A

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

26
Q

what is the negative predictive value

A

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

27
Q

what is venous vs capillary

A

venous is from the vein

capillary is from the capillary

28
Q

how to get capillary blood

A

heel or finger prick

29
Q

why is capillary blood not always identical to venous blood

A

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

29
Q

what does milk the sample mean (capillary blood)

A

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)

30
Q

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

A

the blood clots when it enters

often used when measuring serum ferritin levels

31
Q

most of the blood collecting tubes in NZ are

A

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

32
Q

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

A

has EDTA (anticoagulant) added to it, so the blood doesn’t clot

often used for whole blood count

33
Q

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

A

have gel at the bottom, clot activator and gel separator, has powder that encourages clotting

would replace rep top

34
Q

what are dark blue/black top blood collection tubes

and what are they important for

A

trace element free tube, also prevents clotting

zinc is everywhere so it is super easy to contaminate samples, these are important when measuring zinc

35
Q

what happens to the blood in a purple top

A

the platelets have been stopped from clotting

36
Q

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

A
  • age
  • sex
  • time of day
  • time since last meal
  • presence of symptoms of infections
  • other contributing factors such as oral contraception
37
Q

when collecting zinc blood samples what is important

A

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

38
Q

is plasma and serum often separated in zinc blood samples

A

yes

39
Q

analytical accuracy is ideally determined using

A

certified reference materials

40
Q

venous and capillary blood do not

A

give the same results

41
Q

what is serum

A

Serum is the liquid that remains after the blood has clotted

42
Q

what is plasma

A

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

HUNT 242 (23 decks)

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