Lecture 19: Principles of Biochemical Assessment Flashcards
What are two laboratory methods?
- Static biochemical tests
- Functional tests
What are static biochemical tests?
- Nutrient in biological fluids or tissues
- Urinary excretion rate of nutrient or metabolites
What are functional tests?
- Functional biochemical tests (e.g. glutathione peroxidase activity)
- Functional physiological or behavioural tests (e.g. taste acuity for zinc)
What is precision?
The degree to which repeated measurements of the same biomarker give the same value
What is analytical accuracy?
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
How do you check analytical accuracy?
With certified reference materials
What is analytical sensitivity?
The smallest concentration that can be distinguished from the blank “minimum detection limit”
Values less than the minimum detection limit should…
Not be reported
What is analytical specificity?
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?
When everything else gets burnt off and you are left with your nutrient of interest
What is wet digestion?
Where you are breaking down all of the other organic acid so you know how much of your nutrient you are left with
What is validity?
How well the biomarker correctly describes the nutritional parameter of interest.
What is sensitivity?
How good your method is at identifying people who are cases
What is specificity?
How well does this method identify people who are fine (not cases)
What is predictive value?
the effectiveness of a diagnostic test in predicting the presence or absence of a disease or condition
What is venous blood?
Blood from veins
What is capillary blood?
Blood from capillaries (finger or heal prick)
Why do we use capillary blood?
Less of a burden and less scary
What is milking?
When you try to squeeze blood out extracellular fluid also comes out and the blood is diluted - can lead to haemodilution
What is the standard size of blood collection tubes?
5-10mL
What colour are standard collection tubes?
Red
What are red top tubes used for?
Often used when measuring serum ferritin levels
What happens to blood when it enters red top tubes?
It clots when it enters
Most of the blood collecting tubes in NZ are…
Vacutainers (they have a vacuum in them, supports the blood to fill the tube)
What do lavender / purple top blood collection tubes have added to them?
Has EDTA (anticoagulant) added to it, so the blood doesn’t clot
What are lavender/purple top tubes used for?
Often used for whole blood count
What do the fancy / gold top blood collection tubes have added to them?
have gel at the bottom, clot activator and gel separator, has powder that encourages clotting
What are fancy / gold top blood collection tubes used for?
Would replace red top
How are the dark blue/black top blood collection tubes different?
trace element free tube, also prevents clotting
What are dark blue/black blood collection tubes useful for?
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 tube?
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…
Necessarily 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
What is precision commonly determined by?
Comparing repeated measures of the same pooled sample
Laboratory methods can be divided into….
Static biochemical and functional tests
