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.
How does hyperparathyroidism affect the level of serum phosphorus?
Phosphorus is decreased
What happens to calcium when phosphorus is increased?
It decreases. There is a reciprocal relationship between calcium and phosphorus.
A hospitalized patient exhibits signs of tetany but her ionized calcium is normal. What other analyte should
be checked?
Magnesium. Low levels of magnesium also cause tetany.
How does the reference range for phosphorus in growing children compare to that of adults?
It is higher in children.
What must be done to urine prior to performing a urine phosphorus analysis?
It must be acidified to pH 6 to prevent precipitation of phosphates.
How does hemolysis affect iron level?
Because of the high concentration of iron in hemoglobin, even minimal hemolysis will give falsely elevated results.
To minimize this effect, serum/plasma should be separated from RBCs within one hour of collection and even slightly hemolyzed specimens should not be analyzed.
How are iron levels affected by the time of day when the specimen is drawn?
Iron shows a marked diurnal variation. Levels are approximately 30% higher in the morning.
Which protein transports iron?
Transferrin. It is normally 20-55% saturated with iron.
Where is most of the iron in the body?
In hemoglobin
Name 2 storage forms of iron.
Ferritin is the primary storage form. It is present in most cells and is a readily mobilized form of storage iron. A
small amount of iron is also stored as hemosiderin
How are the iron and total iron binding capacity (TIBC) affected in iron deficiency anemia?
Serum iron is decreased and TIBC is increased. TIBC is an indirect measurement of transferrin. TIBC is
infrequently performed since the development of improved transferrin assays.
What is the most sensitive test for detection of iron deficiency anemia?
Serum ferritin. A decreased serum ferritin is almost always indicative of iron deficiency anemia.
What test results are typical in hereditary hemochromatosis?
Serum iron, ferritin, and transferrin saturation are all increased. Total iron binding capacity is decreased.
What is lactate?
Lactic acid, an intermediary in carbohydrate metabolism. There are 2 types of lactic acidosis:
• Hypoxic, due to decreased oxygen delivery to the tissues
• Metabolic, associated with disease, drugs/toxins, and inborn errors of metabolism
The mortality rate for lactic acidosis is greater than 60%.
Name a reagent used to measure lactate.
Lactate dehydrogenase (LD). Lactate is oxidized to pyruvate by LD in the presence ofNAD+. The NADH formed is measured at 340 nm.
What happens to lactate in the blood following collection?
It increases due to glycolysis.
What is a colligative property?
One that depends on the number of solute particles, regardless of size or molecular weight. The colligative
properties are osmotic pressure, vapor pressure, boiling point, and freezing point.
How is osmolality usually measured in the clinical lab?
By freezing point depression.
What does the urine to serum osmolality ratio indicate?
The degree to which the kidneys concentrate the glomerular filtrate. The normal urine:serum ratio is
1:1- 3: 1.
Which substance contributes most to serum osmolality?
Sodium accounts for almost half.
What are several clinical conditions that result in an increased serum osmolality?
Dehydration, uremia, diabetes mellitus, alcohol intoxication, salicylate intoxication, and excessive electrolyte IVs.
What is osmolal gap?
The difference between measured osmolality and calculated osmolality. It is used to diagnose poisonings and to estimate blood alcohol levels. The reference range is 0-10 mOsm/kg. Higher levels indicate an abnormal
concentration of an unmeasured substance such as isopropanol, methanol, ethylene glycol, or acetone.
Our body exists in two environments including:
External and Internal
This body environment is subject to heat, cold, noise, physical forces, etc.
External
This body environment is relatively constant, consisting of fluids, pH, temperature, electrolytes, etc.
Internal
Roughly _____ of our body weight is fluid
2/3
Body fluids are contained w/in compartments which are separated by a semi-permeable membrane making some ______ and some ______
intracellular fluids, extracellular fluids
All body fluids contain chemical compounds that behave in one of two ways. What are they?
1) remain molecularly intact (urea, creatinine, glucose)
2) break up (dissociate) into separate electrically charged particles known as ions or electrolytes
Any substance which, in solution, dissociates into ions and is thus capable of conducting an electric current
Electrolytes
Electrolytes exist as positively charged particles known as _________, OR negatively charged particles known as __________.
Cations, Anions
The common cations are:
-Sodium
-Potassium
-Calcium
-Magnesium
The common anions are:
-Chloride
-Bicarbonate
-Phosphate
-Sulfate
-Organic Salts
The major electrolytes tested for in the lab are:
-Sodium
-Potassium
-Calcium
-Magnesium
-Chloride
-Bicarbonate
-Phosphorus
Some of the major functions of electrolytes include:
-Maintain osmostic pressure
-Regulate hydration of various body fluid compartments
-Maintain pH
-Regulate proper function of heart and muscles
-Oxidation-reduction reactions
-Essential cofactors for enzymes
The total concentration of cations w/in the body is on average _______, and _________ for anions. In other words, ____ equals _____ making the body fluids always ___________
155 mEq/l, 155mEq/l, positive, negative, electrically neutral
One of the most popular tests ordered by the physician regarding electrolytes
Serum electrolyte profile
A serum electrolyte profile includes:
-Sodium
-Potassium
-Chloride
-Bicarbonate (Carbon dioxide)
In a normal adult, approximately what percentage of the body’s sodium is bound in the bone structure and is nonexchangeable?
30%
Sodium intake is dependent on ________, while sodium output occurs through the ________, ________, and ________.
dietary intake, GI tract, skin, urine
The major route of sodium excretion is:
by the kidneys in urine output
Sodium is freely filtered by the glomerulus, w/ approx. ____ being reabsorbed as normally less than ______ of filtered sodium is actually excreted.
99%, < 1%
As the intake of sodium increases or decreases, excretion of sodium increase or decreases ________, to return the extacellular volume to normal
Proportionally
Excess sodium is termed __________, while a deficiency in sodium is termed __________
Hypernatremia, Hyponatremia
Inflammation or Edema is typically associated with an increased volume of which electrolyte?
sodium
Hypernatremia can be a result of which conditions?
-Cardiac failure
-Liver disease
-Renal disease causing GFR reduction causing decreased sodium filtration
-Hyperalosternoism
-Pregnancy
-CONGESTIVE HEART FAILURE causing less blood to pump causing less sodium to be filtered
Hyponatremia can be caused by:
-GI losses
-Excessive sweating
-Renal disease
-Adrenal insufficiency
-Diuretic therapy
-Osmotic diuresis
-Burns
T or F: Hypernatremia is dependent on the cause, magnitude, and rate in fall of serum sodium
False: Hyponatremia
After partial removal from the plasma by glomerular filtration, how much of the potassium is reabsorbed by the tubules?
Nearly ALL potassium
Almost all of the bodys total potassium is found in the _______ water space.
Intracellular
Total potassium of the body is influenced by which three factors?
Age, sex, and muslce mass (where most body potassium is contained)
Potassium output occurs in small amounts from the _______ and ______, but most output is in the ________.
GI tract, skin, urine
Excess potassium is called ________
Hyperkalemia
Decreased potassium is called
Hypokalemia
Of all the electrolytes which one is most affected by hemolysis?
Potassium
Functions of potassium include:
-Cardiac muscle activity
-Acid/base balance
-Osmotic pressure between intra and extracellular
A direct method used to determine sodium and potassium and chloride
ISE
ISE methods can be used to test which specimens?
Serum, Urine, CSF
Acceptable specimens for sodium and potassium include:
Serum, Lithium Heparinized Plasma, Whole Blood, Urine, and other bdoy fluids
How long should does the tech have to separate the cells from the specimen for sodium and potassium to avoid shifts?
3 hrs.
Can I use a hemolyzed sample for a sodium and potassium test?
No, hemolyzed specimens will release potassium from the cells causing a false increase in potassium
How long is a sodium and potassium and chloride sample good for?
-One week @ refrigerated or room temps
-One year frozen
Along w/ bicarbonate, this is the most commonly analyzed anion
Chloride
Electrolyte that assists w/ acid/base balance, water balance, and the formation of concentrated HCl in gastric fluid in the stomach
Chloride
Chloride increase is termed __________
hyperchloremia
What is the only condition in which chloride excess MAY NOT be associated w/ sodium excess?
Metabolic Acidosis
Decrease in plasma chloride is known as _________
Hypochloremia
What is the only condition in which chloride depletion may occur WITHOUT sodium depletion
Metabolic Alkalosis
These two electrolytes assist in maintaining the acid/base equilibrium between the plasma and the RBCs
Chloride and Bicarbonate
What is the difference in the chloride shift in tissue capillaries and the chloride shift in pulmonary capillaries?
Tissue capillaries = bicarbonate out, chloride in
Pulmonary capillaries = bicarbonate in, chloride out
This electrolyte is also known as carbon dioxide
bicarbonate
Bicarbonate is formed in the kidney by an enzymatic reaction catalyzed by the enzyme ____________
carbonic anhydrase
Electrolyte that controls acid/base balance by maintaining a 20:1 ratio w/ carbonic acid to control blood pH, as well as controlling water balance
Bicarbonate
What is the bicarbonate to carbonic acid ratio maintained?
20:1
This condition is primarily due to an excess of carbon dioxide; increased C02 retention in an excess production of carbonic acid
Respiratory Acidosis
This condition is primarily due to a deficit in carbon dioxide; bicarbonate is converted to carbonic acid in the kidney to compensate and replace the decreasing carbonic acid
Respiratory Alkolosis
Main cause of Respiratory Alkalosis is contributed to:
hyperventilation syndrome seen in hysteria, anxiety, high fever, drugs
When testing samples for carbon dioxide, it is important to remember to:
cap the specimen, as false decrease of carbon dioxide will occur after it is released in as little as 1 hr
What percentage of the magnesium in the body is associated w/ two ions in the bones, Calcium and Phosphorous?
> 50%
This electrolyte is the principle cation of soft tissues
Magnesium
What percent of magnesium in the body is actually in the blood?
1%
The major clinical symptoms of magnesium disorders are _____________ related
Neuromuscular
One method of magnesium measurement involves using this dye for direct determination w/o proteinization by forming a pink magnesium-calmagite complex
Metallochromatic dye
If the specimen is not separated from the clot asap, magnesium will be ___________ due to its elution from the RBCs as the RBCs contain 3x more magnesium than plasma
Falsely increased
Are hemolyzed samples okay for use when detecting magnesium?
No, it will falsely increase the specimen as RBCs contain 3x more magnesium than plasma
The specimen of choice for magnesium detection is:
Serum
This is the most abundant mineral in the body
Calcium
Of the total body calcium, what percentage is located w/in the bones and teeth?
99%
With 99% of total body calcium in the bones and teeth, where does the other 1% lie?
Blood and soft tissues
What is the breakdown of the remaining 1% of total body calcium?
50%- Ionized Free Calcium (active)
45%- Protein-bound (primarily albumin) (inactive)
5%- Organic Complexes
Functions of Calcium include:
-Bone and Teeth formation
-Coagulation factor of blood
-Conduction of nerve impulses
-Muscle contraction and relaxation
-Alters plasma membranes to allow transport of certain ion in and out of the cell
-Essential ingredient of the “glue” in connective tissue
-Cofactor of many enzymes
There is an _________ relationship between calcium and phosphorous.
inverse
Calcium is absorbed in the small intestine and is greatly enhanced by an ________ pH and greatly decreased by an ________ pH
Acid Alkaline
The presence of this is essential to the absorption of calcium
Vitamin D
Calcium is excreted mostly through the ________, as non-absorbed calcium is excreted in the feces.
GI Tract
Hypercalcemia can be caused primarily by:
malignancy, hyperparathyriodism
What calcium disorder is of concern to neonates?
Hypocalcemia
A hormone secreted by the parathyroid glands in response to LOW calcium levels
PTH
Hormone secreted by the thyroid gland in response to HIGH calcium levels
Calcitonin
Active component of Vitamin D; synthesized in the skin when exposed to UV light but may also be ingested in food sources
Calcitriol
What is the principle/methodology for calcium detection?
Metabolic indicator or dyes
What two dyes are widely used today for the metallochromic indicators when testing calcium?
OCPC and Arsenzo III
If an anticoagulant is used ________ and ______ should be avoided as they chelate calcium
EDTA, Oxalates
What percentage of phosphorous is bound up in the bones and teeth?
80%
What are the functions of phosphorous?
-Bone and teeth formation
-Carb metabolism
-Backbone of nucleic acids
-Buffer in acid/base balance
T or F: Phosphorous deficiencies are common
F. Phosphate deficiencies are unheard of due to the abundance of phosphorous in our diets.
Hyperphosphatemia can occur as a result of:
]
-Hypervitaminosis D
-Hypoparathyroidism
-Kidney Failure
Hypophosphatemia can occur as a result of:
-Rickets
-Hyperparathyroidism
-Fanconi Syndrome
Increased calcium levels may cause:
muscle paralysis and coma
This type of specimen will give more accurate results when testing for phosphorous
Fasting specimens
if the concentrations of the two major plasma anions are added and subtracted from the sum of the two major cations, the difference is called the __________.
Anion Gap
What is the formula for the anion gap?
(Na + K) - (Cl + HCO3)
A low anion gap is of some diagnostic value as the most important cause of low anion gap is ____________
Multiple Myeloma
The most significant function of an electrolyte is to:
Acid, base balance
