Unstable Hemoglobinopathies

  • Diagnosis
  • Background
  • Lab Tests
  • References
  • Related Topics
  • Videos

Indications for Testing

  • Unexplained hemolytic anemias
  • Presence of Heinz bodies detected by supravital staining of blood after more common hemoglobinopathies are ruled out by electrophoresis

Laboratory Testing

  • Initial testing – CBC with peripheral smear
    • Usually demonstrates mild anemia with nonspecific findings of hemolysis
    • In hyperunstable hemoglobinopathies– anisocytosis, basophilic stippling, Howell-Jolly bodies common
  • Heat stability and/or heat denaturation – primary diagnostic test for unstable hemoglobins (isopropanol heat stability test)
    • Unstable hemoglobins yield a precipitate – normal hemoglobins do not
    • Can be falsely positive if sample contains >5% HbF (typically neonates); methemoglobinemia
  • Heinz bodies stain – erythrocytes in peripheral blood
    • Requires incubation of erythrocytes with a supravital stain, which show variable positivity for the stain
    • Results unreliable in infants <6 months
  • Hemoglobin electrophoresis or HPLC may detect unstable hemoglobins, but many mutations are not detected
    • Unstable hemoglobin variants undergo rapid denaturation and degradation within the erythrocyte; remaining Hbs may appear relatively normal
      • Severe hemolysis with normal HPLC – consider beta-globin (β-globin) gene sequencing
      • Rare hyperunstable hemoglobins may not be detected by any of the above tests except by globin sequencing

Differential Diagnosis

Hemoglobinopathies are inherited disorders in which hemoglobin production is altered as a result of quantitative or qualitative defects. Qualitative defects are usually due to point mutations and are referred to as structural hemoglobinopathies. Some mutations decrease solubility of hemoglobin and the precipitated hemoglobin decreases survival times of red blood cells (RBCs). These mutations are referred to as unstable hemoglobins.

Epidemiology

  • Incidence – rare
  • Age – neonatal; usually not recognized in the first few months unless related to mutations of gamma-globin (γ-globin) genes

Inheritance

Pathophysiology

  • Unstable hemoglobins exhibit altered solubility due to oxidation of amino acid residues in globin chains by the following pathophysiological interactions
    • Preventing formation of intact hemoglobin tetramer through weakened binding of heme to globin
    • Interfering with secondary and tertiary structures of the subunit
    • Affecting subunit interactions (eg, interference with quaternary structure)
  • Hyperunstable hemoglobins (rare)
    • Barely detectable or undetectable in the hemolysate
    • Presumably synthesized normally but rapidly destroyed because of extreme instability, creating the phenotype of dominant inherited thalassemia
    • Examples include Hb Cervantes, Hb Marañón
  • Heinz bodies (inclusions seen in RBCs) are the product of hemoglobin denaturation and the production of hemichromes
    • Hemichromes are generated when heme is dissociated from globin and binds elsewhere on the globin chain
    • Hemichromes attach to RBC membranes and are more likely to be destroyed in the spleen
    • End result is premature destruction of RBCs with hemolysis and possible anemia
    • Heinz bodies also found in enzymopathies and thalassemia

Clinical Presentation

  • Congenital Heinz body hemolytic anemia
    • Jaundice, anemia, dark urine, leg ulcers, bilirubin gallstones
  • Neonatal syndromes [Hemoglobin Poole and hemoglobin Hasharon (γ-globin mutations)]
    • Neonatal hemolysis – jaundice, anemia
    • Resolves with aging as adult hemoglobin replaces fetal hemoglobin
  • Other presentations
    • Congenital anemia, splenomegaly, pigmented gallstones
    • Mild or minimal anemia with reticulocytosis out of proportion to circulating hemoglobin
    • Drug (eg, sulfonamides) and other oxidant-induced (eg, infection) acute hemolysis
Tests generally appear in the order most useful for common clinical situations. Click on number for test-specific information in the ARUP Laboratory Test Directory.

Heinz Body Stain 0049090
Method: Supravital Stain

Hemoglobin Evaluation with Reflex to Electrophoresis and/or RBC Solubility 0050610
Method: High Performance Liquid Chromatography/Electrophoresis/RBC Solubility

Limitations 

May not detect all hemoglobin variants

Diagnostic errors can occur due to rare sequence variations

Hemoglobin, Unstable 0049020
Method: Visual Identification

Limitations 

Test cannot be used on infants <6 months of age due to physiologically elevated Hb F levels

General References

ACOG Committee on Obstetrics. ACOG Practice Bulletin No. 78: hemoglobinopathies in pregnancy. Obstet Gynecol. 2007; 109(1): 229-37. PubMed

de la Fuente-Gonzalo F, Nieto JM, Ricard P, Anguita J, Martínez R, Cervera A, Villegas A, González FA, Ropero P. Hb Cervantes, Hb Marañón, Hb La Mancha and Hb Goya: Description of 4 new haemoglobinopathies Clin Biochem. 2015; 48(10-11): 662-7. PubMed

Gallagher PG. Diagnosis and management of rare congenital nonimmune hemolytic disease Hematology Am Soc Hematol Educ Program. 2015; 2015: 392-9. PubMed

Jacob HS, Winterhalter KH. The role of hemoglobin heme loss in Heinz body formation: studies with a partially heme-deficient hemoglobin and with genetically unstable hemoglobins. J Clin Invest. 1970; 49(11): 2008-16. PubMed

Kutlar F. Diagnostic approach to hemoglobinopathies. Hemoglobin. 2007; 31(2): 243-50. PubMed

Rund D, Fucharoen S. Genetic modifiers in hemoglobinopathies. Curr Mol Med. 2008; 8(7): 600-8. PubMed

Wajcman H, Traeger-Synodinos J, Papassotiriou I, Giordano PC, Harteveld CL, Baudin-Creuza V, Old J. Unstable and thalassemic alpha chain hemoglobin variants: a cause of Hb H disease and thalassemia intermedia. Hemoglobin. 2008; 32(4): 327-49. PubMed

Yates AM, Mortier NA, Hyde KS, Hankins JS, Ware RE. The diagnostic dilemma of congenital unstable hemoglobinopathies. Pediatr Blood Cancer. 2010; 55(7): 1393-5. PubMed

References from the ARUP Institute for Clinical and Experimental Pathology®

Greene DN, Vaughn CP, Crews BO, Agarwal AM. Advances in detection of hemoglobinopathies Clin Chim Acta. 2015; 439: 50-7. PubMed

Medical Reviewers

Last Update: August 2016