Clinical biochemistry Flashcards
Accuracy
How correct the result is
Precision
How repeatable the result is
Standard deviation
Measure of variability
Average deviation away from the mean
Mean
Average results
Coefficient of variation
Comparison of variability between sets of results
%CV = (SD/mean) x 100
Low CV - low variability
High CV - high variability
Colours associated with wavelengths
If all wavelengths are absorbed - black
If no wavelengths are absorbed - colourless
If one wavelength is absorbed - complementary colour is seen
Complementary colours
Green - red
Blue - orange
Purple - yellow
Beer’s law
[x] proportional to Abs
Lambert’s Law
Abs proportional to pathlength
Beer-Lambert’s law
Abs = Ecl
Beer’s equation
Ctest = (Abstest/Absstd) x Cstd
Limits to Beer’s equation
Molar absorptivity is assumed to be the same
Cuvettes must be equal
Absorbance must be <2.0 or Law deteriorates
Absorbance must be in linear range
Properties of assays
Sample:reagent ratio Reaction time Reaction temperature Linearity max wavelength
Sample:reagent ratio
Reagent needs to be in excess so all solute is converted
Ratio needs to give absorbance of 0.30-0.40
To determine - run trials of different ratios, check absorbance and determine correct ratio
Reaction time
Need to allow enough time for the reaction to be complete
Conduct time trials and plot absorbance vs time
Absorbance needs to be measured at the stationary phase - difference in absorbance <2.5%/min = difference/absorbance at time
Reaction temperature
Room temperature is generally suitable
Temperature is dependent on the type of reaction - human enzyme reactions require a temp of 37c
Linearity
Required for Beers equation to be valid
minimal and maximal concentrations of linear part of a curve
Plot known concentrations against their absorbance and identify linear portion of curve
If a patient sample does not fall in this range, dilute and repeat
Wavelength max
Highest peak of absorbance
Sometimes multiple peaks and need to choose the one with the largest bandwidth
Blank
Blanks contain everything but solute of interest
Essentially zero the spectrophotometer
Accounts for absorbance of light due to reagents, cuvette and water
Standards
Solution of known concentration of analyte
Used in beers equation
Quality control
Commercially purchased product with set control ranges - gives target value and acceptable ranges
QC’s need to be in range for assay to be deemed reliable
Reference intervals
Normal population ranges - range deemed normal for 95% of a population
Desirable range - range deemed to have a desirable effect in analyte is kept in or below this range
Plasma proteins
Enzymes defence transport coagulation buffers fluid balance
Hyperproteinemia
High total protein in the blood
increased protein by hypergammaglobulinemia - polyclonal (normal immune response) or monoclonal (abnormal production)
Decreased intravascular water by dehydration
