Deck 24: Electrolytes and Blood Gases

Question 1

The anticoagulant that is considered best for anaerobic collection of an arterial or venous whole blood specimen for blood gas analysis is:

A) lyophilized heparin.
B) liquid heparin.
C) sodium citrate.
D) EDTA.

Answer 1

lyophilized heparin.

Question 2

Quantitative sweat chloride testing remains the standard for diagnostic testing of cystic fibrosis (CF)because:

A) a total gene deletion of the cystic fibrosis (CF)gene cannot be detected by direct mutational analysis.
B) there are many mutations of the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR)protein and direct mutational analysis is not always informative.
C) a gene deletion on the X chromosome results in loss of an intracellular receptor protein,which can only be detected by protein analysis.
D) an amino acid deletion in the CFTR gene resulting in the loss of electrolyte transport across cell membranes can only be detected by sweat testing.

Answer 2

an amino acid deletion in the CFTR gene resulting in the loss of electrolyte transport across cell membranes can only be detected by sweat testing.

Question 3

Uptake of O₂ by the blood in the lungs is controlled primarily by:

A) the hemoglobin binding capacity of blood.
B) how much hemoglobin A is available to bind O₂.
C) the amount of total CO₂ bound to hemoglobin.
D) the PO₂ of alveolar air.

Answer 3

the PO₂ of alveolar air.

Question 4

Which of the following electrolytes is regulated in part by dietary intake?

A) Chloride
B) Potassium
C) Sodium
D) All of the above

Question 5

The correct formula for calculating plasma osmolality is:

A) 1.86 * Na (mEq/L)+ glucose (mg/dL)+ urea (g/dL).
B) 1.86 * Na (mmol/L)+ glucose (mmol/L)+ urea (mmol/L)+ 9.
C) 1.86 * Na (mmol/L)+ glucose (mmol/L)/18 + urea (mmol/L)/18 + 9.
D) Na (mEq/L)+ glucose (mg/dL)+ urea (mg/dL).

Question 6

In regard to the colligative properties of a solution,the addition of solutes to pure solvent will _____ the vapor pressure of that solution compared with pure solvent.

A) increase
B) decrease
C) not affect

Question 7

The high extracellular concentration of which cation contributes to the osmotic strength of extracellular fluid?

A) Chloride
B) Potassium
C) Sodium
D) Bicarbonate

Question 8

In the Henderson-Hasselbalch equation,the term "pK'" is the:

A) coefficient for oxygen in blood.
B) solubility coefficient for potassium.
C) negative log of hydrogen ion activity.
D) negative log of the combined dissociation constant for carbonic acid.

Question 9

A 24-hour-old infant is tested for quantitative sweat chloride because her older brother was diagnosed with cystic fibrosis.After iontophoresis of pilocarpine nitrate and collection of sweat,the sample is analyzed by coulometric titration.The value of the infant's sweat chloride was 23 mmol/L (reference interval: 29 mmol/L).The next day,the infant's physician calls the laboratory to report that the infant has difficulty breathing and that the parents report the infant's skin tasted salty.The physician is considering a diagnosis of cystic fibrosis.What type of error has likely occurred?

A) The specimen likely evaporated before being analyzed in the laboratory.
B) The infant was tested at too young of an age for accurate results to be obtained.
C) The specimen was collected over a site of a rash and contaminated with serous fluid.
D) The infant's average sweat rate was too high to obtain accurate results.

Question 10

When arterial blood is exposed to air (as in air bubbles in a collection syringe),which one of the following sets of changes occur?

A) PO₂ increased,PCO₂ decreased,pH decreased
B) PO₂ decreased,PCO₂ increased,pH decreased
C) PO₂ increased,PCO₂ decreased,pH increased
D) PO₂ decreased,PCO₂ decreased,pH decreased

Question 11

Historically,chloride was measured in blood by spectrophotometry.Now the methods of choice for chloride measurement include ion-selective electrodes and:

A) enzymatic measurement of acidified chloride.
B) atomic absorption spectrophotometry.
C) immunoassay.
D) coulometric-amperometric titration.

Question 12

The most common laboratory method of sodium/potassium measurement in a high-throughput automated chemistry analyzer is:

A) atomic absorption spectrophotometry.
B) spectrophotometry.
C) indirect ion-selective electrode measurement.
D) direct ion-selective electrode measurement.

Question 13

Which blood gas parameter is most affected by the choice of arterial versus venous blood?

A) pH
B) PCO₂
C) ctCO₂
D) PO₂

Question 14

The PO₂ at which the hemoglobin of the blood is half saturated with O₂ is referred to as:

A) oxygen saturation.
B) oxygen dissociation.
C) P50.
D) the half-life of oxygen.

Question 15

The "electrolyte exclusion effect" is:

A) an underestimation of electrolyte concentration by indirect ISE methods when hyperproteinemia is present.
B) an overestimation of electrolyte concentration by direct ISE measurements only when serum is used.
C) the exclusion of certain solids by increased activity of electrolytes when determining concentration of those solids.
D) the exclusion of electrolytes in certain measurements when pH,PCO₂,and PO₂ are elevated in arterial blood.

Question 16

Which one of the following statements concerning electrolytes and electrolyte measurement is incorrect?

A) Routine laboratory analysis of electrolytes includes measurement of sodium,potassium,chloride,and bicarbonate as total carbon dioxide.
B) Ion-selective electrode measurements are based on the measurement of the potential difference between the ISE and the reference electrode.
C) Whole blood specimens should be stored at 4° C before separation.
D) Specimen requirements for electrolyte analysis include use of unhemolyzed serum or plasma.

Question 17

To stimulate sweating for a quantitative sweat chloride test,_____ is iontophoresed into the skin.

A) pilocarpine
B) chloride
C) epinephrine
D) alcohol

Question 18

Which one of the following is a cause of decreased fractional oxyhemoglobin (FO₂Hb)?

A) Elevated red blood cell (RBC)count
B) Conversion of part of hemoglobin to dyshemoglobin
C) Hyperventilation
D) Change in PCO₂ of arterial blood

Question 19

An increase in blood pH with a concomitant decrease in PCO₂ and a decreased body temperature and 2,3-diphosphoglycerate will cause the oxygen dissociation curve to:

A) shift to the right.
B) shift to the left.
C) remain unchanged.

Question 20

Osmolality is defined as the number of _____ of solution.

A) moles per liter
B) equivalents per liter
C) moles of osmotic substances per kilogram
D) moles of osmotic substances per liter

Question 21

Although aqueous fluid control materials are the most commonly used commercial controls for blood gas and pH measurements,what is their main disadvantage?

A) They are dissimilar to blood by having lower viscosity and surface tension.
B) They must be shaken vigorously before being opened.
C) The buffer that is used contains high levels of lead.
D) They overestimate pH because the buffer is a weak base.

Question 22

In an individual older than 6 months of age,which one of the following laboratory results is usually associated with cystic fibrosis?

A) Sweat chloride concentration greater than 60 mmol/L
B) Sweat chloride less than or equal to 10 mmol/L
C) Sweat chloride concentration greater than 160 mmol/L
D) Sweat chloride concentration between 40 and 60 mmol/L

Question 23

Whole blood specimens stored at 37° C will demonstrate a falsely increased potassium value because of red blood cell hemolysis.

Question 24

The basic methodology used to measure pH,PCO₂,and PO₂ is:

A) tonometry.
B) potentiometry.
C) osmometry.
D) spectrophotometry.

Question 25

The most commonly measured colligative property of urine or plasma that is tested in the clinical laboratory to determine osmolality is:

A) vapor pressure.
B) the boiling point.
C) osmotic pressure.
D) the freezing point.

Question 26

A blood gas parameter is affected by the choice of arterial versus venous blood.What is the reason for the difference in the value of this correctly identified parameter?

A) The pH of arterial blood is significantly higher because oxygen affects it,as noted in the Henderson-Hasselbalch equation.
B) The hemoglobin in arterial blood is much richer in CO₂ because it has just returned from the lungs.
C) PO₂ is generally lower in venous blood after O₂ is released in the capillaries and higher in arterial blood because this blood has passed through the lungs.
D) Arterial blood contains much more

Question 27

An instrument that hemolyzes whole blood by sonication then determines total hemoglobin fractions by spectrophotometry and calculation is called a(n):

A) pulse oximeter.
B) potentiometer.
C) co-oximeter.
D) ion-selective electrode.

Question 28

The specimen of choice for measurement of potassium (K⁺)is plasma because:

A) anticoagulants preserve the potassium ionic activity better than serum.
B) platelets release potassium during the coagulation process in a serum sample.
C) hemolysis is easily avoided when obtaining a plasma sample.
D) the electrolyte exclusion effect is avoided in a plasma sample.

Question 29

A blood sample from an individual with leukemia is submitted for blood gas analysis.The transport of the sample is delayed for approximately an hour before analysis.What affect,if any,will these two variables have on the blood gas analysis results?

A) There will be no effect on any of the blood gas parameters.
B) All blood gas parameters will increase in value with an elevated white blood cell count due to the presence of azurophilic granules.
C) Because of leukocyte glycolysis,pH decreases,PCO₂ increases,and PO₂ decreases.
D) All blood gas parameters will decrease in value because of the leukocytosis-induced hemolysis.