Diagnostics

Hemoglobin C (Hb C)

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Method:
Anticoagulant:
Recommendation:

Method:

Blood Count
Anticoagulant:

EDTA*
Recommendation:

obligatory

Method:

Hemoglobin Differentiation
Anticoagulant:

EDTA*
Recommendation:

obligatory

Method:

Iron Status
Anticoagulant:

Serum**
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Dep. on Blood Count

Method:

Molecular genetics
Anticoagulant:

EDTA***
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once

^{*3 ml EDTA blood (blood count tube), **7.5 ml serum, ***7.5 ml EDTA blood (extra tube)}

Overview
Diagnosis

Hemoglobin C: Overview

Hemoglobin C (Hb C) is based on the exchange of the seventh amino acid of the β-globin chain from glutamate to lysine (HBB:c.19G>A p.Glu7Lys, HbVarID 227). Hb C disease is caused by the homozygous presence of Hb C (HbCC), a combination of Hb C and β-thalassemia (HbC-β-thalassemia), or of Hb C and certain other abnormal hemoglobins. An exception is the combination of Hb C and Hb S, which is treated as sickle cell disease.

Clinically, Hb C disease is similar to sickle cell disease, but the course is milder. However, it can still be associated with severe health problems such as risk of blindness and deafness. The cause is the instability and increased aggregation tendency of hemoglobin C in the deoxygenated state. Depending on the molecular basis, patients show varying degrees of hemolytic anemia. Carriers of Hb C (HbAC) show no clinical signs.

Hemoglobin C: Diagnosis

Diagnosis or exclusion of Hb C disease or carrier status of Hb C is made by a combination of blood count, iron status (in the presence of hypochromia and/or microcytosis), hemoglobin differentiation, and molecular genetic testing in the presence of abnormal findings to confirm the diagnosis.

Hb C heterozygosity shows a normal blood count with normal erythrocyte indices. Patients with Hb C disease show a sickle cell disease-like picture with chronic hemolytic anemia (Hb 10 - 12 g/dL, MCV <75 fl).

Carriers of Hb C show normal iron status. Patients with Hb C disease may show iron overload with elevation of ferritin due to hemolysis.

The distribution of hemoglobin fractions in Hb C variants and different genotypic combinations is shown in the following table:

Genotype	Hemoglobin fractions
Genotype	HbA	HbC	HbF	HbA2	Other Hb-Fraktionen
HbCC	0%	>95%	Ca. 0,5%	Ca. 2,5%	n.d.
HbAC	Ca. 47%	Ca. 50%	<5%	Ca. 3,0%	n.d.
HbC-β⁰-thalassemia	0%	>80%	<20%	>3,5%	n.d.
HbSC, see sickle cell disease

n.d. not detectable

At initial diagnosis, the Hb C-underlying mutation (HBB:c.19G>A p.Glu7Lys, HbVarID 227) is confirmed by sequencing of the β-globin gene HBB. In Hb C disease, molecular genetic deletion analysis of the β-globin gene complex is used to distinguish HbC homozygosity from a combination of Hb C and β-thalassemia.

Bain BJ. Haemoglobinopathy Diagnosis. Wiley-Blackwell 2020;3. Edition.

Busse B et al. Stufendiagnostik der Hämoglobinopathien. LaboratoriumsMedizin 2015;39(5):335-341.

Kohne E. Hemoglobinopathies. Deutsches Ärzteblatt international 2011;108(31-32):532-540.

Thomas L 2022 Labor und Diagnose. www.labor-und-diagnose-2020.de. Ausgabe 30.06.2022.

Status: April 2024

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