Hemoglobinopathy Syndromes

/ Newsletter

2006-10

P8N 2Z6

P.O. Box 3003
Dryden, ON P8N 2Z6
Phone: (807) 223-8264
Fax : (807) 223-7342
e-mail:

Newsletter

2006-10

Hemoglobinopathy Syndromes

Goal:

To provide physicians with information on the appropriate tests to diagnose Hemoglobinopathies.

Definition:

Hemoglobinopathies are the result of a genetic defect in abnormal structure of one of the globin chains of the hemoglobin molecule.

Hemoglobin (Hb) is composed of four subunits, each of which contains a molecule of heme and a globin chain. The major adult hemoglobin is Hb A, which consists of two α and two β globin subunits. The hemoglobinopathies are genetic disorders of globin and can be divided into two broad categories, the hemoglobin variants, in which structurally abnormal globin chains are produced, and the thalassemias, which are the result of deficient production of normal globin chains.

Approximately 25% of the 11,000,000 people in Ontario belong to ethnic groups that are at high risk of being heterozygous carriers for clinically significant hemogloninopathies.

Identification:

The definition of common hemoglobinopathies is important for three reasons:

Diagnosis of serious or life threatening hemoglobin abnormalities due to homozygous or compound heterozygous hemoglobinopathies.

Identification of individuals of reproductive age who are carriers of clinically significant hemoglobin mutations.

Investigation of microcytic anemia in order to prevent erroneous and unnecessary medical intervention for iron deficiency in individuals with thalassemia trait.

Diagnosis:

Diagnosis of hemoglobinopathies relies on identification and often quantitation of hemoglobin variants. Identification is aided by patient history and clinical presentation due to the genetic etiology of hemogloninopathies.

Recommendations:

Once patient history is taken, the Laboratory recommends the following screening tests:

Figure 1:

CBC
Decreased / MCV / Normal or Increased
RBC Morphology / RBC Morphology
Hypochromic, variations in size and shape, / Hypochromic, variations in size and shape,
Target cells, some nucleated RBC’s. / Target cells, some nucleated RBC’s,
/ Pronounced cells shapes (ie. sickle)
Phenotypic appearance? / Phenotypic appearance?

Thalassemia trait (normal or near normal Hb, increased erythrocyte count*)

Normal
Sickling abnormality

Thalassemia intermedia (more severe presentation than thalassemia trait, non-transfusion dependant)

Hemolytic anemia
Erythrocytosis

Thalassemia major (transfusion dependant thalassemia)

Cyanosis

Consider / Consider
α thalassemia / Hb S
Hb H disease / Hb C
β thalassemia / Hb D
Β thalassemia / Hb E
Hb E / Rare Hb variants
Hb Lepore / Hereditary persistence of fetal hemoglobin
Hb Constant Spring

* A normal RDW is not a reliable indicator of the presence of thalassemia trait.

Further investigation should include:

Hemoglobin Electrophoresis

For additional assistance in diagnosing hemoglobinopathies, refer to Figures 2 – 5.

Figure 2: Algorithm for interperting the hemoglobinopathy investigation results of patients with decreased MCV.

Decreased MCV
Hb A2 Level /

0.036 – 0.08, Hb A>0.90 = β Thalassemia Trait

Normal /

Greater than 0.08 = Hb variant running in conjunction with Hb A2, e.g. Hb E

Consider Hb Variants that present with the thalassemia phenotype, eg:

-Hb E
-Hb Lepore
-Hb H
-Hb Constant Spring

See Figure 4: Interpretation of hemoglobinopathy screenresults for Hb variants associated with the thalassemia phenotype

/ Hb Variant Detection Technique /

See Figures 4 and 5 for the interpetation of β Thalassemia Trait in conjunction with various

Hb variants.

No variant detected
Hb F Level /

0.05– 0.20Hb = β Thalassemia Trait

Normal /

Hb F markedly increased, Hb A reduced or absent = β

Thalassemia Intermedia or Major
* Proceed to Figure 3: Investigation for α Thalassemia trait.

Figure 3: Investigation for α thalassemia trait.

Decreased MCV, Normal Hb A2 and Hb F level, No Hb Variants Detected
Hb H Inclusion Bodies /

Hb H bodies = Many = Hb H Disease or Hb H/Constant Spring Disease

Hb H bodies negative /

Hb H bodies = Occasional = a Thalassemia Trait

No / Patient involved in a pregnancy or planned pregnancy? / Yes
Ferritin Level /
Decreased / Normal or increased / History of Chronic or
Inflammatory Disease / Investigate for
α thalassemia by DNA techniques regardless
of ferritin level
Iron deficiency / Yes / No
Anemia of
Chronic Disease / Suggestive of
α thalassemia trait

Figure 4: Interpretation of hemoglobinopathy screen results for Hb variants associated with the thalassemia phenotype.

Note: Hb fraction quantities are approximate values and will vary depending on the method

used and the individual patient presentation.

Hb E detected / / Typical presentations

Hb A >0.50, Hb E 0.25 – 0.30 = Hb E trait*
Hb A absent, Hb E 0.85 – 0.95, Thalassemia trait phenotype = Homozygous Hb E**
Hb A absent, Hb E present, Hb F >0.20, Thalassemia intermeia or major pehenotype = Hb E/β thalassemia***

Other presentations

Hb E <0.20, Low MCV = Hb E trait with concomitant a thalassemia

* Hb E trait presents with an MCV ranging from slightly decreased to normal.
** Homozygous Hb E presents with a decreased MCV.
*** Hb A2 is not measurable in the presence of Hb E. Differentiation of Hb E//β
thalassemia from homozygous Hb E is based on pnehotypic appearance, and family study.
Hb Lepore detected / / Typical presentations

Hb A >0.70, Hb Lepore 0.08 – 0.15 = Hb Lepore trait*
Hb A absent, Hb Lepore present, Hb F >0.20 = Hb Lepore/β thalassemia or Homozygous Hb Lepore

* The presence of a low MCV with a variant running to the position of Hb Lepore
and quantifying between 0.08 – 0.15 is diagnostic of Hb Lepore trait.
Hb H detected / / Typical presentations

Hb A >0.80, Hb H 0.02 – 0.10, Numerous H inclusive bodies = Hb H disease
Hb A >0.70, Hb H 0.11 – 0.25, Numerous H inclusive bodies = Suspect Hb H/Constant Spring Disease*

* Hb H/Constant Spring disease has a more severe phenotype than Hb H disease.
Situations where Hb H quantifies at greater than 0.10 should warrant a careful
examination of the electrophoresis or chromatography to determine if Hb Constant Spring is present.
Increase Hb F detected / / Typical presentation

Hb A >0.80, Hb F 0.05 – 0.20, decreased MCV*, normal Hb A2 = β thalassemia trait

* See Figure 5 for the interpretation of increased levels of Hb F not associated with
the thalassemia phenotype.

Figure 5: Interpretation of hemoglobinopathy screen results for Hb variants not associated with the thalassemia phenotype.

Note: Hb fraction quantities are approximate values and will vary depending on the method used

and the individual patient presentation.

Hb S detected / / Typical presentations

Hb A >0.50, Hb D 0.35 – 0.45 = Hb D trait*
Hb A absent, Hb D 0.85 – 0.95, Normal Hb A2** = Homozygous Hb D
Hb A absent, Hb D 0.85 -= 0.95, Low MCV, Increased Hb A2** = Hb D/βthalassemia

Other presentations

Hb A >0.50, Hb C <0.30, Low MCV = Hb C trait with concomitant α thalassemia
Hb A absent, Hb F 0.20 – 0.30, Hb C = 0.65 – 0.75 = Hb C/HPFH
Hb A <0.040, Hb C >0.50, Low MCV, Increased Hb As* = Hb C/β+thalassemia
Hb A absent, Hb C 0.85 – 0.95, Normal Hb As*, Low MCV = Hb C disease with concomitant α thalassemia

* Measurement of Hb As in the presence of Hb C is possible with HPLC only.
Increased Hb F detected / / Typical presentations

Hb A >0.50, Hb F 0.10 – 0.30, normal MCV = Heterozygous HPFH

Other presentations

Hb A absent, Hb F 0.85 – 0.95, normal Hb and MCV = Homozygous HPFH
Hb A >0.80, Hb F 0.02 – 0.05, normal MCV = mild HPFH or increased Hb F secondary to another condition, eg. pregnancy, or myelodysplastic syndrome

Hb D detected* / / Typical presentations

Hb A >0.50, Hb D 0.35 – 0.45 = Hb D trait
Hb A absent, Hb D 0.85 – 0.95, Normal Hb A2** = Homozygous Hb D
Hb A absent, Hb D 0.85 – 0.95, Low MCV, Increased Hb A2** = Hb D/β thalassemia

Other presentations

Hb A > 0.50, Hb D <0.30, Low MCV = Hb D trait with concomitant α thalassemia
Hb A absent, Hb F 0.20 – 0.30, Hb D = 0.65 – 0.75 = Hb D/HPFH
Hb A <0.40, Hb D >0.50, Low MCV, Increased Hb A2** = Hb D/β+ thalassemia

* Identification of Hb D is presumptive in most laboratories and relies on:

The detection of a β chain variant ie. Quantifies at >0.30 in the heterozygous state.
Electrophoretic or chromatographic criteria consistent with Hb D.
No hematological abnormality.

** Measurement of Hb A2 in the presence of Hb D can be done by HPLC. With manual chromatography, a method capable of measuring HB A2 in the presence of Hb D is required.
Rare Hb Variants detected / / Typical presentations

Hb A >0.50, Rare Hb Variant >0.30 = Heterozygous for a rare β Chain Hb variant
Hb A >0.65, Rare Hb Variant <0.25 = Heterozygous for a rare α Chain Hb variant

Other presentations

Hb A Absent, Low MCV, Rare Hb Variant Present = Compound Heterozygous rare Hb variant with thalassemia trait

Reference:

QMP-LS, Good Practice Guidelines for the Laboratory Investigation of Hemoglobinopathies. Hematology-General, Volume 3, Section 1.2.1., pg 21. October 2, 2001.

Acknowledgments:

The Kenora-Rainy River Regional Laboratory Program, Inc. and its Managers have prepared this Newsletter. It can also be found on our website

Dr. MacDonald would be pleased to discuss this perspective with you at his next onsite visit.

We’d like to hear from you!!

Was this article helpful? Are there other topics you would like information on?

Let us know by contacting your Laboratory Manager or,

Anna Robinson

Regional Laboratory Consultant

Kenora-Rainy River Regional Laboratory Program, Inc.

P.O. Box 3003, Dryden, ON P8N 2Z6

Phone: 807-223-8264 Fax: 807-223-7342

e-mail:

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