Lecture 19: Principles of Biochemical Assessment

Question 1

What are two laboratory methods?

Answer 1

1. Static biochemical tests
2. Functional tests

Question 2

What are static biochemical tests?

Answer 2

• Nutrient in biological fluids or tissues
• Urinary excretion rate of nutrient or metabolites

Question 3

What are functional tests?

Answer 3

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

Question 4

What is precision?

Answer 4

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

Question 5

What is analytical accuracy?

Answer 5

The difference between the reported and the true amount of the nutrient present in the sample is a measure of the analytical accuracy (“trueness”) of the laboratory test

Question 6

How do you check analytical accuracy?

Answer 6

With certified reference materials

Question 7

What is analytical sensitivity?

Answer 7

The smallest concentration that can be distinguished from the blank “minimum detection limit”

Question 8

Values less than the minimum detection limit should…

Answer 8

Not be reported

Question 9

What is analytical specificity?

Answer 9

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

Question 10

How can analytical specificity be enhanced?

Answer 10

By dry ashing or wet digestion

Question 11

What is dry ashing?

Answer 11

When everything else gets burnt off and you are left with your nutrient of interest

Question 12

What is wet digestion?

Answer 12

Where you are breaking down all of the other organic acid so you know how much of your nutrient you are left with

Question 13

What is validity?

Answer 13

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

Question 14

What is sensitivity?

Answer 14

How good your method is at identifying people who are cases

Question 15

What is specificity?

Answer 15

How well does this method identify people who are fine (not cases)

Question 16

What is predictive value?

Answer 16

the effectiveness of a diagnostic test in predicting the presence or absence of a disease or condition

Question 17

What is venous blood?

Answer 17

Blood from veins

Question 18

What is capillary blood?

Answer 18

Blood from capillaries (finger or heal prick)

Question 19

Why do we use capillary blood?

Answer 19

Less of a burden and less scary

Question 20

What is milking?

Answer 20

When you try to squeeze blood out extracellular fluid also comes out and the blood is diluted - can lead to haemodilution

Question 21

What is the standard size of blood collection tubes?

Answer 21

5-10mL

Question 22

What colour are standard collection tubes?

Answer 22

Red

Question 23

What are red top tubes used for?

Answer 23

Often used when measuring serum ferritin levels

Question 24

What happens to blood when it enters red top tubes?

Answer 24

It clots when it enters

Question 25

Most of the blood collecting tubes in NZ are…

Answer 25

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

Question 26

What do lavender / purple top blood collection tubes have added to them?

Answer 26

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

Question 27

What are lavender/purple top tubes used for?

Answer 27

Often used for whole blood count

Question 28

What do the fancy / gold top blood collection tubes have added to them?

Answer 28

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

Question 29

What are fancy / gold top blood collection tubes used for?

Answer 29

Would replace red top

Question 30

How are the dark blue/black top blood collection tubes different?

Answer 30

trace element free tube, also prevents clotting

Question 31

What are dark blue/black blood collection tubes useful for?

Answer 31

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

Question 32

What happens to the blood in a purple top tube?

Answer 32

The platelets have been stopped from clotting

Question 33

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

Answer 33

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

Question 34

When collecting zinc blood samples what is important?

Answer 34

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

Question 35

Is plasma and serum often separated in zinc blood samples?

Answer 35

Yes

Question 36

Analytical accuracy is ideally determined using…

Answer 36

Certified reference materials

Question 37

Venous and capillary blood do not…

Answer 37

Necessarily give the same results

Question 38

What is serum?

Answer 38

Serum is the liquid that remains after the blood has clotted

Question 39

What is plasma?

Answer 39

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

Question 40

What is precision commonly determined by?

Answer 40

Comparing repeated measures of the same pooled sample

Question 41

Laboratory methods can be divided into….

Answer 41

Static biochemical and functional tests