ASCP MLS Clinical Chemistry Exam
Questions & Answers (Grade A+
Which of the following represents the Henderson-Hasselbalch
equation as applied to blood pH?
A. pH = 6.1 + log HCO3-/PCO2
B. pH = 6.1 + log HCO3-/(0.03 × PCO2)
C. pH = 6.1 + log dCO2/HCO3-
D. pH = 6.1 + log (0.03 × PCO2)/HCO3- -
correct answer ✅B. The Henderson-Hasselbalch equation
describes the pH of a buffer comprised of a weak acid and its salt.
pH = pKa + log salt/acid, where pKa is the negative logarithm of the
dissociation constant of the acid. In this case, the salt is sodium
bicarbonate and the acid is the dissolved CO2, which is equal to
0.03 (mmol/L per mm Hg) x PCO2. The pKa includes both the
hydration and dissociation constant for dissolved CO2 in blood, 6.1
and is termed pK´.
What is the PO2 of calibration gas containing 20.0% O2, when the
barometric pressure is 30 in.?
A. 60 mm Hg
B. 86 mm Hg
C. 143 mm Hg
,ASCP MLS Clinical Chemistry Exam
Questions & Answers (Grade A+
D. 152 mm Hg -
correct answer ✅C. Convert barometric pressure in inches to mm
Hg by multiplying by 25.4 (mm/in.). Next, subtract the vapor
pressure of H2O at 37°C, 47 mm Hg, to give dry gas pressure.
Multiply dry gas pressure by the %O2:
25.4 mm/in. × 30 in. = 762 mm Hg
762 mm Hg - 47 mm Hg (vapor pressure) = 715 mm Hg (dry gas
pressure)
0.20 × 715 mm Hg = 143 mm Hg PO2
What is the blood pH when the partial pressure of carbon dioxide
(PCO2) is 60 mm Hg and the bicarbonate concentration is 18
mmol/L?
A. 6.89
B. 7.00
C. 7.10
D. 7.30 -
correct answer ✅C. Solve using the Henderson-Hasselbalch
equation.
pH = pK´ + log HCO3-/(0.03 × PCO2), where pK´, the
,ASCP MLS Clinical Chemistry Exam
Questions & Answers (Grade A+
negative logarithm of the combined hydration and dissociation
constants for dissolved CO2 and carbonic acid, is 6.1 and 0.03 is the
solubility coefficient for CO2 gas.
pH = 6.1 + log 18/(0.03 × 60) = 6.1 + log 18/1.8
pH = 6.1 + log 10. Because log 10 = 1, pH = 7.10
Which of the following best represents the reference (normal)
range for arterial pH?
A. 7.35-7.45
B. 7.42-7.52
C. 7.38-7.68
D. 6.85-7.56 -
correct answer ✅A. The reference range for arterial blood pH is
7.35-7.45
and is only 0.03 pH units lower for venous blood owing to the
buffering effects of hemoglobin (Hgb) known as the chloride
isohydric shift. Most laboratories consider less than 7.20 and
greater than 7.60 the critical values for pH.
, ASCP MLS Clinical Chemistry Exam
Questions & Answers (Grade A+
What is the normal ratio of bicarbonate to dissolved carbon dioxide
(HCO3-:dCO2) in arterial blood?
A. 1:10
B. 10:1
C. 20:1
D. 30:1 -
correct answer ✅C. When the ratio of HCO3-:dCO2 is 20:1, the log
of
salt/acid becomes 1.3. Substituting this in the Henderson-
Hasselbalch equation and solving for pH gives pH = 6.1 + log 20; pH
= 6.1 + 1.3 = 7.4. Acidosis results when this ratio is decreased, and
alkalosis when it is increased.
What is the PCO2 if the dCO2 is 1.8 mmol/L?
A. 24 mm Hg
B. 35 mm Hg
C. 60 mm Hg
D. 72 mm Hg -
correct answer ✅C. Dissolved CO2 is calculated from the
Questions & Answers (Grade A+
Which of the following represents the Henderson-Hasselbalch
equation as applied to blood pH?
A. pH = 6.1 + log HCO3-/PCO2
B. pH = 6.1 + log HCO3-/(0.03 × PCO2)
C. pH = 6.1 + log dCO2/HCO3-
D. pH = 6.1 + log (0.03 × PCO2)/HCO3- -
correct answer ✅B. The Henderson-Hasselbalch equation
describes the pH of a buffer comprised of a weak acid and its salt.
pH = pKa + log salt/acid, where pKa is the negative logarithm of the
dissociation constant of the acid. In this case, the salt is sodium
bicarbonate and the acid is the dissolved CO2, which is equal to
0.03 (mmol/L per mm Hg) x PCO2. The pKa includes both the
hydration and dissociation constant for dissolved CO2 in blood, 6.1
and is termed pK´.
What is the PO2 of calibration gas containing 20.0% O2, when the
barometric pressure is 30 in.?
A. 60 mm Hg
B. 86 mm Hg
C. 143 mm Hg
,ASCP MLS Clinical Chemistry Exam
Questions & Answers (Grade A+
D. 152 mm Hg -
correct answer ✅C. Convert barometric pressure in inches to mm
Hg by multiplying by 25.4 (mm/in.). Next, subtract the vapor
pressure of H2O at 37°C, 47 mm Hg, to give dry gas pressure.
Multiply dry gas pressure by the %O2:
25.4 mm/in. × 30 in. = 762 mm Hg
762 mm Hg - 47 mm Hg (vapor pressure) = 715 mm Hg (dry gas
pressure)
0.20 × 715 mm Hg = 143 mm Hg PO2
What is the blood pH when the partial pressure of carbon dioxide
(PCO2) is 60 mm Hg and the bicarbonate concentration is 18
mmol/L?
A. 6.89
B. 7.00
C. 7.10
D. 7.30 -
correct answer ✅C. Solve using the Henderson-Hasselbalch
equation.
pH = pK´ + log HCO3-/(0.03 × PCO2), where pK´, the
,ASCP MLS Clinical Chemistry Exam
Questions & Answers (Grade A+
negative logarithm of the combined hydration and dissociation
constants for dissolved CO2 and carbonic acid, is 6.1 and 0.03 is the
solubility coefficient for CO2 gas.
pH = 6.1 + log 18/(0.03 × 60) = 6.1 + log 18/1.8
pH = 6.1 + log 10. Because log 10 = 1, pH = 7.10
Which of the following best represents the reference (normal)
range for arterial pH?
A. 7.35-7.45
B. 7.42-7.52
C. 7.38-7.68
D. 6.85-7.56 -
correct answer ✅A. The reference range for arterial blood pH is
7.35-7.45
and is only 0.03 pH units lower for venous blood owing to the
buffering effects of hemoglobin (Hgb) known as the chloride
isohydric shift. Most laboratories consider less than 7.20 and
greater than 7.60 the critical values for pH.
, ASCP MLS Clinical Chemistry Exam
Questions & Answers (Grade A+
What is the normal ratio of bicarbonate to dissolved carbon dioxide
(HCO3-:dCO2) in arterial blood?
A. 1:10
B. 10:1
C. 20:1
D. 30:1 -
correct answer ✅C. When the ratio of HCO3-:dCO2 is 20:1, the log
of
salt/acid becomes 1.3. Substituting this in the Henderson-
Hasselbalch equation and solving for pH gives pH = 6.1 + log 20; pH
= 6.1 + 1.3 = 7.4. Acidosis results when this ratio is decreased, and
alkalosis when it is increased.
What is the PCO2 if the dCO2 is 1.8 mmol/L?
A. 24 mm Hg
B. 35 mm Hg
C. 60 mm Hg
D. 72 mm Hg -
correct answer ✅C. Dissolved CO2 is calculated from the
