Hb electrophoresis

Hemoglobin abnormalities not uncommonly occur as compound disorders (2
or more mutations) that can have complex interactions and variable phenotypes. Although powerful as an
adjunct for a complete and accurate diagnosis, genetic methods alone can give incomplete and possibly
misleading information due to limitations of the methods. Interpretation of genetic data requires the
incorporation of protein analysis results. This profile is well-suited for the classification of hemoglobin
disorders. A large number (>1,000) of variants of hemoglobin (Hb) have been recognized. They are
identified by capital letters (eg, Hb A or Hb S), or by the city in which the variant was first discovered
(eg, Hb Koln). Clinical symptoms that can be associated with hemoglobin disorders include microcytosis,
sickling disorders, hemolysis, erythrocytosis, cyanosis/hypoxia, long-standing or familial anemia,
compensated or episodic anemia, and increased methemoglobin or sulfhemoglobin results. Mayo Clinic
Laboratories receives specimens for this test from a wide geographic area and nearly one-half of all
specimens received exhibit abnormalities. The most common abnormality is an increase in Hb A2 to
about 4% to 8%, which indicates beta-thalassemia minor in the correct clinical context. A wide variety of
other hemoglobinopathies also have been encountered. Ranked in order of relative frequency, these are:
Hb S (sickle cell disease and trait), C, E, Lepore, G-Philadelphia, H, D-Los Angeles, Koln, Constant
Spring, O-Arab, and others. Hb C and S are found mostly in people from west or central Africa and Hb E
and H in people from Southeast Asia. Hemoglobin electrophoresis is often used in the evaluation of
unexplained microcytosis, thus accounting for the frequent detection of Hb Lepore, which is relatively
common in Italians and others of Mediterranean ancestry and in Hb E, which is relatively common in
Southeast Asians resettled in the United States; microcytosis is characteristic of both Hb Lepore and Hb
E. Alpha-thalassemia is very common in the United States, occurring in approximately 30% of African
Americans and accounting for the frequent occurrence of microcytosis in persons of this ethnic group.
Some alpha-thalassemias (ie, hemoglobin variants H, Barts, and Constant Spring) are easily identified in
the hemoglobin electrophoresis protocol. However, alpha-thalassemias that are from only 1 or 2
alpha-globin gene deletions are not recognized by protein studies alone. For the diagnosis of
alpha-thalassemias, deletion and duplication testing is required.
Useful For: Diagnosis and comprehensive classification of thalassemias and hemoglobin variants