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Monday, 30 September 2019

DETECCIÓN DE HEMOGLOBINA C HOMOCIGOTA ANTE PRESENCIA DE ERITROBLASTOS

Written by Fernando Calvo Boyero | Javier Hernando Redondo | Anna Marull Arnall, Posted in Volumen11

Figure 1. Scattergram WDF (WBC differential) (a) y WNR (white cell nucleated) (b) where the erythroblasts population is indicated.

We present the case of a 40-year-old male patient from Mali who routinely visits his health center.

In the complete blood count highlights a hemoglobin of 14.1 g/dL (Reference Value [RV]: 13.5-17.2) with an erythrocytosis (5.58 x106 RBC/ul, RV: 4-5) and a decreased Mean Corpuscular Volume [MCV](71.3 fL; RV: 80-100) and Mean Corpuscular Hemoglobin [MCH] (25 pg; RV: 27-33). Iron profile was normal.
In the complete blood count analysis (Sysmex XN Series, Kobe, Japan), normal leukocyte populations are detected, but an erythroblasts population of 3.6 cells per 100 leukocytes was founded (Figure 1) together with a reticulocytosis (3.3%; RV: 0.5-2). The analyzer displays the flags "NRBC_Present" and "Fragments?". Given these results, a peripheral blood smear was performed.

Examination of peripheral blood smear shows a marked anisopoikilocytosis with abundant dysmorphic forms  (target cells and eccentrocytes) and some erythroblasts (4 per 100 leukocytes) compatible with a hemoglobinopathy (Figure 2a), so we added a variant hemoglobins study by HPLC (High Performance Liquid Chromatography).

Hemoglobin variant studies (Figure 2b) performed by HPLC (Variant II, BioRad) demonstrated a normal HbF (0.2%; RV:<1%), normal HbA2 (3%; VR: 2.5-3.5) and elevated HbC (93.8%; VR 0%), consistent with homozygous hemoglobinopathy C.

Figura2Figure 2. A) Peripheral smear shows abundant target cells, eccentrocytes and cells with irregular hemoglobin distribution. There is also a hemoglobin crystal (arrow). B) Separation of the Hemoglobin chains by HPLC. It shows a majority peak of Hemoglobin C and the absence of hemoglobin A.

Hemoglobin C is a variant hemoglobin with a mutation in the beta globin gene at the same position as hemoglobin S, but with a different amino acid change pero con diferente cambio de aminoácido (α2β26Glu→Lys)1

This hemoglobin is native from East Africa, at the east of the Niger River. In the case of Mali, where the patient originates from, the prevalence in some areas is greater than 10%. This high prevalence has been related to the protective effect it produces on Plasmodium falciparum infections2.

In these patients we can found from a normal concentration of hemoglobin to a mild or moderate anemia (8 g / dl). There is usually a marked microcytosis, as well as a MCHC at the high limit of normality. Due to chronic hemolysis, the reticulocyte count is usually slightly elevated, usually 2-4%, and also patients may present splenomegaly and cholelithiasis.

In the HPLC study, a hemoglobin C is usually found that corresponds to almost all the amount of hemoglobins. Fetal hemoglobin may be slightly elevated, but usually does not exceed 3%.

Reference

  1. Bain BJ. Hemoglobinopathy Diagnosis, Second Edition. Blackwell Publishing. 2006.
  2. Travassos MA, Coulibaly D, Laurens MB, Dembélé A, Tolo Y, Koné AK, et al. Hemoglobin C Trait Provides Protection From Clinical Falciparum Malaria in Malian Children. J infect Dis. 2015 Dec 1; 212(11): 1778-1786
 

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