Electrolytes and Blood gases

Question 1

1. The most common method for measuring sodium and
   potassium is
   a. flame emission spectrophotometry.
   b. enzymatic methods.
   c. atomic absorption spectrophotometry.
   d. ion-selective electrode

Answer 1

d. ion-selective electrode

Question 2

2. Which of the following will shift the O2 dissociation
   curve to the right?
   a. Hyperthermia
   b. Acute alkalemia
   c. Hypocapnia
   d. Low 2,3-DPG

Answer 2

a. Hyperthermia

Question 3

3. Which of the following present the least risk of erroneous
   blood gas values?
   a. 30 minutes at ambient temperature
   b. WBC >100,000/μL
   c. Air bubbles in the sample
   d. First drop from a capillary puncture

Answer 3

a. 30 minutes at ambient temperature

Question 4

4. The vapor pressure osmometer has fallen out of popular
   use due to several technical drawbacks. Which of the following are false regarding this instrument?

a. It does not include any volatile solutes in its measurement of serum osmolality.
b. It is sensitive to changes in ambient temperature.
c. It contains a thermistor, a galvanometer, and a measuring potentiometer.
d. It would be able to detect an increase in osmolality
attributable to increased blood glucose.

Answer 4

a. It does not include any volatile solutes in its measurement of serum osmolality.

Question 5

5. Recent developments in genetic testing, paired with
   advances in understanding genotype-phenotype correlations in cystic fibrosis, have broadened the testing
   options for this serious condition. Currently the gold
   standard test for the diagnosis of cystic fibrosis is:

a. sweat conductance.
b. sweat chloride.
c. immunoreactive trypsinogen.
d. assay to detect common mutations.
e. gene sequencing to detect common and novel
mutations.

Answer 5

b. sweat chloride.

Question 6

6. Solutes change the behavior of the solvent to which they
   are added in predictable ways, conferring colligative
   properties to the solution, including
   a. decreased osmotic pressure.
   b. increased vapor pressure.
   c. decreased boiling point.
   d. decreased freezing point.
   e. increased transmittance

Answer 6

d. decreased freezing point.

Question 7

7. The most common cause of falsely elevated sweat chloride testing results is
   a. eczema.
   b. improper gauze placement.
   c. hypothyroidism.
   d. postcollection evaporation.
   e. analytic error.

Answer 7

d. postcollection evaporation.

Question 8

8. What is the expected effect on plasma K+ concentration
   if a freshly drawn sample is stored on the bench for 1.5
   hours prior to being centrifuged?

a. An increase in plasma K+ of ∼2 mmol/L
b. A decrease in plasma K+ of ∼0.2 mmol/L due to transcellular shift into RBCs
c. An insignificant increase in plasma K+ of ∼0.2 mmol/L
d. A decrease in plasma K+ due to increased hemolysis
e. A decrease in plasma K+ ∼2 mmol/L due to transcellular shift into RBCs

Answer 8

c. An insignificant increase in plasma K+ of ∼0.2 mmol/L
d. A decrease in plasma K+ due to increased hemolysis

Question 9

9. Hemolysis of a plasma sample will most likely affect which of the following, and why?

A. sodium; it is present in equal amounts both intracellularly and extracellularly
B. glucose; it moves out of cells into plasma
C. insulin; it is the major intracellular anion and is present in high amounts in RBC’s
D. potassium; it is localized mainly within cells, particularly RBC’s

Answer 9

D. potassium; it is localized mainly within cells, particularly RBC’s

Question 10

10. Which of the following equations is the correct Henderson-Hasselbalch equation?
    a. pK′ + pH + log [cHCO3]/[cH2CO3]
    b. pK′ + pH + log [cH2CO3]/[cHCO3]
    c. pH + pK′ + log [cHCO3]/[c H2CO3]
    d. pH + pK′ + log [cH2CO3]/[cHCO3]

Answer 10

c. pH + pK′ + log [cHCO3]/[c H2CO3]