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HUNT242 > Lecture 19 > Flashcards

Lecture 19 Flashcards

Principles of Biochemical Assessment

1
Q

forms of nutritional assessment

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

Subclinical deficiency

A

Before you get any clinical signs

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3
Q

There are two methods that 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

Precision

A

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

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8
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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9
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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10
Q

Analytical accuracy

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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11
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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12
Q

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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13
Q

Analytical sensitivity

A

the smallest concentration that can be distinguished from the blank

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14
Q

what 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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15
Q

Analytical specificity

A

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

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16
Q

how can analytical specificity be enhanced

A

by dry ashing or wet digestion

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17
Q

what is dry ashing

A

Burning the sample which is then used to enhance analytical specificity

18
Q

what is wet digestion

A

breaking down all the other organic material used to enhance analytical specificity

19
Q

Validity

A

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

20
Q

what is an example of validity

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

21
Q

Key aspects of validity

A
  • the assay must be appropriate for the study objective
  • drugs, hormones, infection may alter laboratory test results but not actual status
22
Q

What is sensitivity

A

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

23
Q

what is specificity

A

How well does the method identify people who are fine

24
Q

What is the positive predictive value

A

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

25
Q

What is the negative predictive value

A

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

26
Q

What is a venous vs capillary

A

venous is from the vein

capillary is from the capillary

27
Q

How to get capillary blood

A

Heal prick or finger prick

28
Q

when you squeeze the blood out you are not just getting capillary blood you are also getting (milk the sample)

A

the fluid as well which dilutes it= can lead to haemodilution

29
Q

Red top blood collection tubes

This is often used to measure

A

The blood clots when it enters

Often used when measuring serum ferritin levels

30
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)

31
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

32
Q

What are the fancy / gold top blood collection tubes

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

33
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

34
Q

what happens to the blood in a purple top

A

the platelets have been stopped from clotting

35
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
36
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

37
Q

is plasma and serum often separated in zinc blood samples

A

yes

38
Q

analytical accuracy is ideally determined using

A

certified reference materials

39
Q

venous and capillary blood do not

A

give the same results

40
Q

what is serum

A

Serum is the liquid that remains after the blood has clotted

41
Q

what is plasma

A

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

HUNT242 (23 decks)

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