Electrolytes Flashcards
What are the three main electrolytes of interest?
Sodium
Potassium
Chloride
What is the main extracellular ion in blood?
Sodium
What panel of tests are electrolytes measured as part of?
Renal panel
When might a “direct” test be needed for electrolytes?
HILLS test interference
i.e. lipaemic or haemolysed sample
What is a “direct” sodium test?
This is whereby sodium in a patient’s sample is determined using ion selective electrodes
Where are direct tests for analytes carried out?
Direct tests are carried out on the blood gas analysers
What is meant by the indirect measurement of electrolytes?
Whereby electrolytes are measured on the automated analyser
The sample of serum or plasma is diluted before analysis
What might cause an artificially lower sodium when measured indirectly on the analyser?
What might cause an incorrectly low sodium?
Massive hyperlipidemia -> high lipids -> HILLS test -> lipaemic sample
Massive proteinuria -> high protein
Why does hyperlipidaemia or proteinuria cause a reduced sodium level?
These artifacts in blood reduce the proportion of plasma that is water thereby reducing the measured sodium concentration
“electrolyte exclusion effect/volume displacement effect”
What is the main reason why direct sodium might be required?
Pseudohyponatraemia
Explain what is meant by Ion selective electrodes
An analytical technique used to determine the activity of ions in aqueous solution by measuring the electrical potential
Explain the principle behind ion selective electrodes
A selective membrane is applied to the ion selective electrode -> this allows only the ion of interest to be measured -> membrane used will only let the ion of interest through
We measure the potential of two solutions of already-known ion concentration and make a plot of the measured potential and logarithm of the ion concentration
Based on this plot, the ion concentration of an unknown solution can be known by measuring the potential and corresponding it to the plot
(I dont understand this)
What tests are double dipped?
(3)
Sodium
Calcium
ALK
Pre-analytical factors that interfere with K+
Sample left in fridge/cold room prior to separation/centrifugation
