Electrolytes Flashcards
What are the major electrolytes?
Sodium, potassium, chloride, and bicarbonate
What is the major extracellular cation?
sodium
What is the major intracellular cation?
Potassium
What is the major extracellular anion?
Chloride
Which hormone regulates the concentration of sodium?
Aldosterone
Why should standards for sodium be stored in plastic containers instead of glass?
Sodium can leech from glass containers and cause falsely elevated values.
How are sodium and potassium usually measured?
By ion selective electrodes (ISE).
What is the approximate ratio of potassium between RBCs and serum?
20: 1. This explains why hemolysis must be avoided when measuring potassium.
What are several factors that can cause artifactual (false) elevations of potassium?
Fist clenching, prolonged tourniquet time, contamination with K2EDTA or IV fluid, hemolysis, thrombocytosis,
and leukocytosis.
Why is potassium slightly higher in serum than in plasma?
Because potassium is released from platelets during clotting.
Before reporting an elevated potassium, what should be checked?
The specimen should be checked for hemolysis or excessive delay in separating the serum/plasma from the RBCs. Either could be responsible for a false elevation.
What clinical condition results from very high or very low potassium levels?
Cardiac arrhythmias.
What is chloride’s role in the body?
It maintains hydration, osmotic pressure, and electrolyte balance.
What is pilocarpine?
A topical drug used in the sweat test to stimulate sweat glands.
In iontophoresis, an electric current delivers
pilocarpine nitrate to the sweat glands on the forarm or thigh. Sweat is collected and chloride is measured. A source of error is failure to collect an adequate volume of sweat. The sweat test should be performed at a CF Foundation accredited care center.
What happens to CO2 if the sample is exposed to air?
It decreases
What does anion gap measure?
Unmeasured anions. The anion gap is increased with renal failure, diabetic acidosis, lactic acidosis, and the presence of drugs or toxins.
What is the most abundant mineral. in the body?
Calcium
Which form of calcium is physiologically active?
Ionized
Why is pH an important consideration in ionized calcium determinations?
As pH decreases (acidosis), calcium dissociates from its complexed forms, increasing the amount of free ionized
calcium in the serum
What is the commonly used method for total calcium?
A dye-binding reaction with ortho-cresolphthalein complexone (CPC) or arsenazo III. Atomic absorption is the
reference method but rarely used in clinical labs.
How is ionized calcium measured?
By ion selective electrodes.
What substances regulate calcium levels?
PTH, calcitonin, and vitamin D.
What is tetany?
Muscle spasms, cramps, and irritability due to decreased calcium or magnesiu
What is the most common cause of hypercalcemia?
Primary hyperparathyroidism.