L19 - principles of biochemical assessment

What is a static biochemical test?

measure nutrient in biological fluids or tissues e.g. plasma nutrient, or urinary excretion of a nutrient

What is a functional biochemical test?

measuring a nutrient dependent enzyme, or measuring e.g. taste acuity for zinc (functional physiological/behavioural test)

What is precision and how to measure it?

repeatability, do repeated measures of the same test give the same value? done by repeated measures on pooled samples either within-run or between run (something to do with sample measurement is changed)

What is analytical accuracy and how to measure it?

difference between reported and true amount of nutrient in a sample is a measure of lab test ‘trueness’, measure with spiked samples (known amount of nutrient added to see if test detects all), certified reference materials (bought with a known amount of nutrient to test along with own assay), and analysis of pooled sample by multiple labs using different methods

What is analytical sensitivity?

smallest concentration that can be distinguished from the blank/minimum detection limit, any values < than this shouldn’t be reported

What is analytical specificity?

ability of a method to measure exclusively the substance of interest, particiularly for minerals can be enhanced by dry ashing or wet digestion

What is validity?

how well the biomarker correctly describes the nutrient of interest, lab test results can be affected by drugs, hormones and infection

What is predictive value?

the likelihood of the test classifying the person correctly

Venous vs capillary blood?

capillary blood may be affected by haemodilution as squeezing the finger may result in ECF mixing with blood

What is the difference between plasma and serum?

plasma is the blood in body (still contains fibrinogen as presence of an anticoagulant stops clotting) while serum is what is separated from a blood clot, most nutrients can be measured in both

How to measure zinc in the body?

requires a stainless steel needle, a trace element free blood collection tube, information on time of day, time since last meal and symptoms of infection