Diagnosis and Characterization of Hb C/Hb Iowa: A Rare but Easily Misidentified Compound Heterozygous Condition

Abstract

Hb Iowa is a rare hemoglobin (Hb) variant with a Gly --> Ala substitution at position 119 of beta-globin. It was previously reported only in an African American infant who was also heterozygous for Hb S [beta6(A3)Glu --> Val] and her mother (Hb A/Iowa). Here we describe the second report of Hb Iowa, the first in conjunction with Hb C [beta6(A3)Glu --> Lys]. The patient was an African American girl, originally diagnosed as homozygous Hb C during neonatal screening. When seen in our clinic, hematological data for both the child and her mother (Hb C trait) indicated mild anemia with slightly low mean corpuscular volume (MCV) but normal red blood cell (RBC) count. Analysis of blood from the child by capillary isoelectric focusing (cIEF) identified Hb C and an unknown Hb variant with an isoelectric point (pI) intermediate to that of Hbs F and A. The unknown variant was identified as Hb Iowa by DNA sequence analysis of the beta-globin gene (GGC --> GCC). Both reported cases of Hb Iowa indicated that there are no abnormal hematological manifestations associated with this rare Hb variant. In both cases, however, Hb Iowa was mistaken for Hb F during routine neonatal screening by high performance liquid chromatography (HPLC) and/or gel IEF. Neonatal misidentification of Hb Iowa led to misdiagnosis of sickle cell disease and Hb C disease, respectively. In our patient, Hb Iowa was also misidentified as Hb A at 2 years of age by a commercial reference laboratory using cellulose acetate and citrate agar gel electrophoresis. This led to an incorrect diagnosis of Hb C trait. These results show that commonly used analytical methods can easily misidentify Hb Iowa as Hbs F or A in neonates, or older individuals, resulting in incorrect identification of the Hb phenotype. We conclude that the presence of Hb Iowa, or other variants with similar pIs, should be considered in cases where the results of follow-up testing conflict with neonatal diagnosis of sickle cell or Hb C disease, or where clinical presentation does not agree with diagnosis of either homozygous or heterozygous Hb S or Hb C.

Association between Inflammation and Biological Variation in Hemoglobin A1c in U.S. Nondiabetic Adults

“…Numerous studies have shown, however, that variation in HbA1c in human populations cannot be fully explained by interindividual variation in MBG (1)(2)(3)(4)(5)(6). In vivo and in vitro studies suggest that HbA1c levels are influenced by erythrocyte turnover, pH, and other factors besides blood glucose concentration (1,2,5,(7)(8)(9)(10)(11). Moreover, clinical studies have convincingly demonstrated that some individuals and racial groups have persistently lower or higher than expected HbA1c levels compared with others with similar blood glucose levels (2)(3)(4)(5)(6)(11)(12)(13).…”

CE‐based analysis of hemoglobin and its applications in clinical analysis

“…Certain variants, such as Hb A and Hb C are of too small molecular weight difference to be resolved; nevertheless, the mutation could induce a sufficiently large change in pI (0.4 pH units) to allow their complete separation by CIEF (more common Hb variants' pI values are listed in Table 1). Most of the pioneering works were demonstrated by Hempe and Craver et al [21][22][23][24][25][26][27][28], whose first-hand experimental results showed that the CIEF technique was reproducible, objective and specific for many abnormal Hb variants, and has proven to be superior to most conventionally and routinely used assay techniques.…”