237. Fetal Hemoglobin

Question 1

What is fetal hemoglobin (HbF)?

Answer 1

A physiologic variant of adult hemoglobin (HbA) primarily present in the fetus.

Question 2

How does the oxygen affinity of HbF compare to HbA?

Answer 2

HbF has a higher oxygen affinity than HbA.

Question 3

What is the predominant hemoglobin in newborns?

Answer 3

HbA.

Question 4

What factors can affect the transition from HbF to HbA?

Answer 4

• Transfusion with HbA blood
• Premature birth

Question 5

What controls RBC production in the fetus?

Answer 5

Fetal growth factors.

Question 6

What is the first form of hemoglobin present in the embryo?

Answer 6

Embryonic hemoglobin (Hbε or hemoglobin epsilon).

Question 7

When does the liver begin producing fetal hemoglobin?

Answer 7

At 6 weeks gestational age (wGA).

Question 8

What is the composition of fetal hemoglobin (HbF)?

Answer 8

• Two α (alpha) subunits
• Two γ (gamma) subunits.

Question 9

What happens to HbF around 32 weeks gestational age?

Answer 9

HbF begins to be replaced by HbA.

Question 10

What percentage of fetal hemoglobin does HbF account for at 40 weeks gestational age?

Answer 10

70%.

Question 11

What is the correlation between HbF and hemoglobinopathies?

Answer 11

HbF is selected for in hemoglobinopathies such as sickle cell disease and thalassemia.

Question 12

True or False: HbF levels typically wane to negligible levels 6 months after birth.

Answer 12

True.

Question 13

What is the P50 value for HbF?

Answer 13

19 mm Hg.

Question 14

What is the P50 value for HbA?

Answer 14

26.8 mm Hg.

Question 15

What is hydroxyurea used for in sickle cell patients?

Answer 15

It increases the level of HbF and reduces sickling.

Question 16

What should be included in the history of a patient with hematologic disorders?

Answer 16

History of prematurity and current postconceptual age.

Question 17

How can the mean corpuscular volume (MCV) relate to HbF levels?

Answer 17

A higher MCV reflects a higher proportion of HbF.

Question 18

Fill in the blank: The relationship between HbF and MCV can be represented by the equation HbF (%) = (2.6 × MCV) - _______.

Answer 18

215.5.

Question 19

What happens to the oxygen-hemoglobin dissociation curve after a neonate with HbF receives a transfusion?

Answer 19

It shifts to the right.

Question 20

What is the significance of SO2 in anesthetic monitoring?

Answer 20

It is a crucial parameter for intravascular oxygen content and tissue delivery of oxygen.

Question 21

What is the optimal systemic oxygen saturation for equal pulmonary and systemic blood flows?

Answer 21

80%.

Question 22

How does the blood gas analyzer preset for HbF differ for a term newborn versus one who has received HbA transfusion?

Answer 22

• Term newborn: 80% HbF preset
• Transfused newborn: 0% HbF preset.

Question 23

What can cause an increase in the partial pressure of oxygen (PO2) required for a certain oxygen saturation (SO2) after transfusion?

Answer 23

A decrease in HbF levels.