Serum Potassium Test Flashcards
is the major intracellular cation.
Potassium
Major intracellular cation in the body
Potassium
concentration____ times greater inside the cell than outside
20
only___% of total body K+ circulates in the plasma (___% is intracellular)
2%
98%
FUNCTIONS
• Regulation of neuromuscular excitability
• Contraction of the heart
• Intracellular fluid (ICF) volume
• H+ (hydrogen ion) concentration
Tissue buffering in acidosis can lead to
^ plasma [K*]
Tissue buffering in alkalosis can lead to
v plasma [K*]
Causes of artifactual hyperkalemia (false increase):
- Coagulation process & Thrombocytosis
- Prolonged tourniquet application
- Excessive clenching of fists during blood collection
- Storage of blood sample in ice
- Hemolysis (most common)
Coagulation process & Thrombocytosis: During clot formation, platelets release______, and in thrombocytosis (elevated platelet count), the excess platelets further contribute to the release of potassium, leading to_____
potassium
falsely elevated levels.
Prolonged tourniquet application: Prolonged pressure from a tourniquet can trap blood and reduce circulation, leading to ______from cells, which____ potassium in the sample.
potassium leakage
elevates
Excessive clenching of fists:
The cause of this______ potassium during fist clenching is a local effect caused by release of potassium from muscle during muscle contraction in the forearm.
increased
Storage of blood sample in ice:
Cold temperatures can cause red blood cell damage, leading to the release of intracellular potassium, resulting in _____potassium levels.
falsely elevated
The rupture of red blood cells during sample collection or handling releases intracellular potassium into the plasma, the most common cause of falsely high potassium readings.
Hemolysis:
• Slight hemolysis (______): increases..
50mg/dL of Hgb
^ 3%
• Gross hemolysis (_____): increases…
> 500mg/dL of Hgb
^ 30%
How is falsely increased results prevented (due to clotting reasons)
situation may be avoided by using a
heparinized tube to prevent clotting of the specimen
How is falsly incrrased results prevented (due to hemolysis)
by using proper care in the drawing of blood.
How is falsely increased results prevented (due to improper storage)
storing blood on ice promotes the release of K+ from cells, whole blood samples for K+ determinations should be stored at room temperature (never iced) and analyzed promptly or centrifuged to remove the cells.
• Specimen:
- Serum
- Plasma (AOC: Heparin)
- Urine (24-hour urine)
_______is the anticoagulant of
choice.
Whereas serum and plasma generally give similar K+ levels,_____ reference intervals tend to be slightly
higher.
Heparin
serum
Why is potassium higher in serum than in plasma?
Because clotting promotes release of potassium
Significantly elevated platelet counts may result in the release of K+ during clotting from rupture of these
cells, causing a spurious hyperkalemia. In this case, _______is preferred.
plasma
T or F
Whole blood samples may be used
with some analyzers. Consult the instrument’s opera-
tions manual for acceptability.
True
Urine specimens should
be collected over a____-hour period to eliminate the influence of diurnal variation.
24
METHODS
Colorimetric Methods
Ion Selective Electrode (ISE)
Colorimetric Methods
Lockhead and Purcell Method
Lockhead and Purcell Method
• Potassium is reacted with_____ to produce_______
sodium cobaltinitrite
sodium potassium cobaltinitrite
Lockhead and Purcell Method
With the addition of_____ (color developer), a____ color is produced and determined spectrophotometrically
phenol
blue
Ion Selective Electrode (ISE)
• Uses_____ and ______ as inner electrolyte solution
valinomycin membrane and KCI
• Current method of choice
Ion Selective Electrode (ISE)
REFERENCE RANGES FOR POTASSIUM
Serum
3.5-5.1 mmol/L
REFERENCE RANGES FOR POTASSIUM
Plasma
Males: 3.5-4.5 mmol/L
Females: 3.4-4.4 mmol/L
REFERENCE RANGES FOR POTASSIUM
Urine
25-125 mmol/d
Principle
Agappe
Sodium Tetraphenylborate + Potassium –—> Potassium Tetraphenylborate + Sodium
Agappe
Potassium is estimated by_____ method.
The extent of turbidity is____ to the potassium concentration and is measured photometrically at
_______nm
Turbidimetric
proportional
578 nm (570-620 nm)
Potassium Reagent
Sodium tetraphenylboron (TPB-Na) 0.2 mol/1
Potassium standard
Potassium Standard Concentration 5 mmol/L
Agappe
Reagent Preparation
Potassium Reagent and Standard are ready to use.
Agappe
Reagent Storage and Stability
The sealed reagents are stable up to the expiry date stated on the label, when stored at______ and_____
2 - 8°C and protected from light
Agappe
Open Vial Stability
Once opened, the reagent is stable up to_____, if contamination is avoided.
4 weeks
Agappe
Standard and sample amount
25 microliters
Standard and sample amount
25 pL
Agappe amount of reagent
1000 microliters
Agappe
Mix well and incubate ____for ___ minutes.
Measure the absorbance of Standard (Abs.S) and test sample (Abs.T) against_____ at____ with in____
at room temperature
5
distilled water
578 nm
10 minutes
Agappe
Reference Range
It is recommended that each laboratory should establish its own reference values.
The following value may be used as guide line.
Serum/Plasma: ______
3.6 - 5.5 mmol/L
Agappe
Linearity
This reagent is linear up to______
14 mmol/L.
Agappe
If the concentration is greater than linearity (14 mmol/L), dilute the sample with…
normal saline and repeat the assay. Multiply the result with dilution factor.
Potassium is the most abundant
Intracellular cation
Name the Colorimetric method for Potassium determination?
Lockhead & Purcell Method
What is the color developer used in the Lockhead & Purcell Method?
Phenol
What are the causes of artifactual hyperkalemia?
Thrombocytosis
Prolonged tourniquet application
Excessive clenching of fists
Storage of blood sample in ice
Hemolysis
What is the reference range for serum potassium?
3.5-5.1 mmol/L
