see Thalassemias

Fetal hemoglobin is composed of 2 α chains has and two γ chains : its affinity for O2 is greater than hemoglobin A. It disappears progressively after birth to be replaced by HbA. The normal concentration of HbF is < 1 % at 12 months of age.

It is still present in significant amounts in cases of thalassemia or homozygous sickle cell disease. 

Its concentration may increase in case of:

-        myelomonocytic syndromes  of the child, or primary myelofibrosis

-         pernicious anemia, Fanconi or Blackfan-Diamond

-         significant increase of erythropoiesis (after hemorrhage, for example).

-         mutation of loci involved in the quantitative production of HbF (QTL): HBFQTL1 (11p15.4), HBFQTL2 (6q23), HBFQTL3 (Xp22. 2), HBFQTL5 (2p15) [MIM 142 335], HBFQTL6 (KLF1 gene at 19p13) and HBFQTL4 (8q), which interacts with the XmnI-G-gamma polymorphism of HBG2. to influence HbF production.  

There is also the hereditary persistence of fetal hemoglobin [MIM 141 749], a rare disease of autosomal dominant transmission found mainly in the black population. It results from p11.15 deletions in the beta-globin gene region (e.g., the delta-globin gene) or point mutations in promoter regions of the HBG1 or HBG2 genes. 

A distinction is made between :

- heterozygous: presence of 5 to 30 % HbF, asymptomatic

- homozygous: presence of 100 % HbF, no consequence other than a leftward deviation of the hemoglobin dissociation curve.

Anesthetic implications: 

complete blood count; pulse oximetry: the presence of large quantities of HbF increases SpO2 when paO2 varies from 50 to 100 mmHg. 

The Kleihauer test, designed to detect the presence of fetal cells in maternal blood in the event of fetomaternal hemorrhage, is falsely positive in patients with abnormally high HbF levels.

References :

-        Picard L, Delabaere A, Serre Sapin A-F, Giansily Blaizot M, Gallot D.
Test de Kleihauer « faussement » positif et syndrome héréditaire de persistance de l’hémoglobine fœtale.
Gynécologie Obstétrique Fertilité & Sénologie 2019 ; 47 : 612-4

Updated: January 2024