Recognition of rare hemoglobin variants by hemoglobin A1c measurement procedures

[Effects of Hemoglobin Variants on Glycosylated Hemoglobin Testing]

Objective

To examine the common types of hemoglobin variants and to evaluate the influence of common variants on the results of two kinds of glycosylated hemoglobin (HbA1c) tests.

Methods

We conducted a retrospective study, analyzing the data of a patient population undergoing two HbA1c tests, high performance liquid chromatography (HPLC) and capillary electrophoresis (CE), at West China Hospital, Sichuan University between March 2021 and February 2022. By screening the chromatograms, the hemoglobin variants were identified and their migration positions in the CE method were recorded. The effects of the variants with different migration positions on the findings of the two methods were compared. Variant samples with different migration positions were selected and Sanger sequencing was performed to determine mutations in HBA1, HBA2, and HBB genes in the variant samples.

Results

We examined the HbA1c of 207 786 patient samples, identifying variant peaks in the chromatograms of 372 patients. The detection rate of variants was 0.18%, with the variant identification rate of HPLC being 43.3% and that of CE, 100%. Through sequencing, 20 variants were detected. A total of 261 patient samples were tested for HbA1c with both HPLC and CE. HPLC reported all HbA1c results, while CE did not report HbA1c results for 28 samples, among which, 26 showed abnormal peaks that overlapped with HbA1c peaks, and 2 showed abnormal peaks that overlapped with HbA0 peaks. The commonly observed variant migration positions, as revealed by CE, were at the horizontal coordinates of 225±1, 200±3, 100±2, 124±1, 70±2, and 182±1. There was significant difference between HPLC method and CE method in the determination of HbA1c ( P<0.0083), and the difference between the two methods was the largest when there were variants in the 200±3 region. Linear regression showed that the correlation of HbA1c results between the two methods was different when different regional variants were present, and that the correlation between the two methods was strongest when 124±1 region was present ( r=0.998).

Conclusion

There are diverse types of hemoglobin variants and most of them can affect the HbA1c findings of HPLC. Analyzing the chromatogram facilitates the identification of the variants.

The pivotal role of HbA1c assay to detect hemoglobinopathies: A 5-year observational retrospective study in the population of Southern France

Background and Aims

Mobility and migration flows are growing from different countries of the world to European countries, including France and in particular the Mediterranean basin. This study aimed to investigate the presence of hemoglobin (Hb) variants in outpatients/inpatients of the Montpellier Hospital (France) in whom an HbA1c assay had been performed and for which the country of birth had been informed.

Methods

This is a retrospective study from January 2016 to December 2020 based on all high-performance liquid chromatography (HPLC) chromatograms (Tosoh Bioscience HLC-723G8) having an alarm of suspected Hb variant during HbA1c measurement. The corresponding samples were systematically sent to the hematology laboratory for confirmation and identification of Hb variant. Patient's medical history, clinical and demographic data were extracted from each medical chart. Statistical analyses were performed using XLSTAT® software, version 2016.06.35661.

Results

Three hundred sixty-three patients were confirmed with Hb variant exhibiting 17 different Hb profiles, highlighting the pivotal role of glycated hemoglobin (HbA1c) as a detection step. The prevalence of Hb variant in this southern French population was 0.71%, with the highest frequency for the beta-globin variants (n = 342/363; i.e., 94.2%), including the most common: S, C, E, and D in 200/342 (58.5%), 83/342 (24.3%), 29/342 (8.5%), and 11/342 (3.2%), respectively. Among patients with Hb variants, almost half (165/363; i.e., 45.4%) were born in the African continent with a predominance for Morocco (32/165; i.e., 19.3%) and Algeria (29/165; i.e., 17.5%).

Conclusion

HbA1c assay is a useful tool to detect Hb variants. Hemoglobinopathies are a public health issue in the current French population which is a multiethnic society. Despite the monocentric nature of our study, we note a high frequency of Hb variants in the south of France, which underlines the importance of screening for Hb variants in the whole population.

The Hemoglobin Wayne Variant and Association With Falsely Elevated HbA1c

The objective of this work is to explain the effect of the clinically silent hemoglobinopathy hemoglobin Wayne (Hb Wayne) variant on glycated hemoglobin A1c (HbA1c) assay. This variant can result in falsely high HbA1c values among euglycemic individuals without diabetes mellitus (DM). We discuss 3 patients who were diagnosed with type 2 DM based on spuriously high HbA1c values due to the presence of Hb Wayne. All 3 patients were found to have elevated HbA1c values that did not correlate with other glycemic parameters such as capillary blood sugar, 2-hour oral glucose tolerance test, and fructosamine levels. Hemoglobin electrophoresis revealed that each patient had a rare hemoglobinopathy called Hb Wayne variant. These patients were reassured that they did not have DM and were able to avoid unnecessary treatment. These cases emphasize the importance of clinical judgment in recognizing the limitations and caveats of the HbA1c test. It is always necessary to investigate further any discordance between HbA1c values and the clinical picture or other glycemic parameters.

Discordantly high HbA1c may assist in diagnosing α-thalassemia but not diabetes: A case report

Glycated hemoglobin (HbA1c) is an important method for monitoring blood glucose and diagnosing diabetes. High‐performance liquid chromatography is more commonly used in the laboratory for the detection of HbA1c. Although HbA1c detected by high‐performance liquid chromatography is susceptible to abnormal hemoglobin, there are few reports that it is affected by α‐thalassemia. Previous reports have generally concluded that α‐thalassemia does not affect or lower HbA1c. Here, we report a case of discordantly high HbA1c inconsistent with fasting blood glucose. Finally, the patient was diagnosed with α‐thalassemia and insulin resistance. α‐Thalassemia might lead to a discordantly high HbA1c result, which could be attributed to elevated hemoglobin H. In this case, glycated albumin might accurately reflect the real average level of blood glucose. When finding discordant HbA1c, patients should be advised to undergo thalassemia and hemoglobinopathy screening by diabetologists/endocrinologists or primary care physicians to avoid a missed diagnosis of hematopathy.

Two co-inherited hemoglobin variants revealed by capillary electrophoresis during quantification of glycated hemoglobin

OBJECTIVES

The observation of numerous new structural defects in hemoglobin (Hb) has often been linked to the evolution and development of device technologies used for the separation and quantification of hemoglobin components. However, the increased use of preventive tests for hemoglobinopathies and separative methods to quantify glycated hemoglobin (HbA_1c) also contributed to these observations, as demonstrated by the case described here. Our aim is to emphasize that different separative method can provide more useful information in patient management.

METHODS

A 64-year-old diabetic woman of Moroccan descent was examined in the context of HbA_1c monitoring. The test was performed using high performance liquid chromatography (HPLC) and capillary electrophoresis (CE) systems. Molecular characterization was performed by direct sequencing of the β and α globin genes.

RESULTS

The two methods used showed the presence of an anomalous fraction identified as HbS, already observed previously, but only through CE it was possible to observe the presence of another variant and its hybrid components. Direct sequencing of β and α globin genes confirmed heterozygous HbS [β6 (A3) Glu→Val; HBB: c.20A>T] and allowed to identify a mutation on the α ₂, [α114 (GH2) Pro→Leu gene; HBA2: c.344C>T] corresponding to the rare Hb Nouakchott variant.

CONCLUSIONS

The two Hb variants highlighted by the EC and the molecular characterization therefore allowed adequate advice, the correct assessment of HbA_1c and metabolic status and therefore better clinical management of the patient. The availability of different instruments in the same laboratory, confirming situations of diagnostic uncertainty, represents a valuable opportunity that should be encouraged.

Hemoglobin Wayne causing a falsely elevated hemoglobin A1c

Hemoglobin A1c (HbA1c) is an important tool for diagnosis and management of patients with diabetes mellitus (DM). However, hemoglobin variants can interfere with laboratory assays and lead to inaccurate results. This study describes a patient who was found to have falsely elevated HbA1c values secondary to hemoglobin Wayne, a rare hemoglobin variant. Although hemoglobin Wayne is often clinically silent, falsely elevated HbA1c results could lead to unnecessary medical interventions that could cause patient harm. This variation in results highlights the importance of utilizing additional measurements such as glucose readings and evaluating for hemoglobin variants when results are discordant.

A Comparative Evaluation of Capillary Electrophoresis, Cation-Exchange High-Performance Liquid Chromatography, and Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry for the Screening of Hemoglobin Variants

OBJECTIVES

The present study was conducted to evaluate the usefulness of capillary electrophoresis (CE), cation-exchange high-performance liquid chromatography (HPLC), and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) for the screening of hemoglobin (Hb) variants prevalent in southern China.

METHODS

A total of 102 types of Hb variants in 1,083 variant carriers were identified over a 5-year period. These variants were analyzed by a CE method (Capillarys 3 TERA), a cation-exchange HPLC analyzer (Variant II Turbo 2.0), and a MALDI-TOF MS system (QuanTOF).

RESULTS

The presence of 85 (83.3%, 85/102), 84 (82.4%, 84/102), and 62 (60.8%, 62/102) Hb variants was detected by Capillarys 3 TERA, Variant II Turbo 2.0, and QuanTOF, respectively. Of the three methods, only Capillarys 3 TERA recognized all 10 of the most frequent Hb variants in southern China. There were six, two, and three Hb variants that can only be detected by Capillarys 3 TERA, Variant II Turbo 2.0, and QuanTOF, respectively. The detection limit of mass difference for QuanTOF was approximately 11 to 20 Da.

CONCLUSIONS

MALDI-TOF MS is suitable for use as an auxiliary method rather than a stand-alone method for the screening of Hb variants prevalent in southern China.

A Novel α-Globin Chain Variant, Hb Nanchang [HBA2: c.46G>A, Codon 15 (GGT>AGT) (Gly→Ser)], Detected by Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry

Here we report a new α chain variant accidentally discovered during Hb A_1c measurement by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry (MS) that revealed the presence of a variant α chain with a mass of 15155 Da. However, this hemoglobin (Hb) variant cannot be detected by the first-line methods such as cation exchange high performance liquid chromatography (HPLC) and capillary electrophoresis (CE). Sanger sequencing confirmed the presence of a heterozygous missense mutation [HBA2: c.46G>A, codon 15 (GGT>AGT), (Gly→Ser)]. The theoretical mass difference (30 Da) due to the substitution of amino acid glycine to serine matched the actual measured mass difference (29 Da). As this is the first report of the mutation, we named it Hb Nanchang after the place of residence of the proband.

Hemoglobin Fukuoka caused unexpected hemoglobin A1c results: A case report

BACKGROUND

Glycated hemoglobin (Hb) (HbA_1c) is an indicator that is used to diagnose and monitor the treatment of diabetes. Many factors can affect the detection of HbA_1c. One of the most important of these factors is the Hb variant. Here, we report a rare Hb variant and evaluate its effect on HbA_1c.

CASE SUMMARY

A 35-year-old man was suspected of harboring an Hb variant following the measurement of HbA_1c with the Variant II Turbo 2.0 Hb detection system during a routine examination. Subsequently, we used the Arkray HA-8160 and ARCHITECT c4000 system to reanalyze HbA_1c. Finally, the Hb variant was detected with a Capillary2FP analyzer that operates on the principle of capillary electrophoresis. We also used gene sequencing to investigate the mutation site. The value of HbA_1c detected with the Variant II Turbo 2.0 system was 52.7%. However, the Arkray HA-8160 system did not display a result while the ARCHITECT c16000 system showed a result of 5.4%. The Capillary2FP analyzer did not reveal any abnormal Hb zones. However, gene sequencing identified the presence of a mutation in the Hb β2 chain [CD2(CAC>TAC), His>Tyr, HBB: c.7C>T]; the genotype was Hb Fukuoka.

CONCLUSION

Hb variants could cause abnormal HbA_1c results. For patients with Hb variants, different methods should be used to detect HbA_1c.

Signature of Glycylglutamic Acid Structure

BACKGROUND

Glutamate (Glu) is of great interest in biomedical research. It is considered a biomarker in diabetes, which may potentially contribute to the development of autism in genetically vulnerable human populations, and it is found in relation to advanced glycation end products (AGEs) [1]. Additionally, Glu plays an active role in the function of ligand-gated ion channel glutamate receptors, chloride channels capable of filtering glutamate, as well as Potassium (K+)-channel [2]. Glu attains α [3] and β [4] crystal forms and Cβ-CH2 show asymmetric 1H signal pattern in NMR spectra.

OBJECTIVES

The current study was undertaken to understand the signal patterns of Cβ-CH2 in Glu of the smallest dipeptide, Glycylglutamic Acid (GlyGlu), as well as the order, and planarity of the amide bond in the molecule.

MATERIALS AND METHODS

NMR spectra of GlyGlu were measured in D2O to deduce 1H and 13C chemical shifts and coupling constants. GlyGlu was crystallized from MeOH and the structure was determined by single crystal X-ray diffraction techniques.

RESULTS

The sidechain of Glu in the dipeptide dissimilates the β form. The amino group of Gly (Glycine) is protonated and exhibits hydrogen bonding with the main chain carboxylate group of a symmetry-related Glu that is deprotonated in the crystal packing of GlyGlu. The deprotonated main chain carboxylate of Glu is also in hydrogen-bonding distance from the side chain carboxylic acid group that is in the protonated form of a symmetry-related Glu of the dipeptide. The Cβ-CH2 geminal protons on the side chain of Glu have different chemical shifts and splitting pattern in 1H NMR reflecting their dissymmetric environment.

CONCLUSION

The results reported will be useful for monitoring changes that Glu and/or molecules in connection to Glu may undergo in in vivo, in situ, and in vitro conditions. This provides a valuable metric which will enable the examination of the metabolites relevant to the detection and diagnosis of disease or developmental conditions, as well as scrutinizing the effectiveness of treatment options.

Hemoglobin Yamagata [β132(H10)Lys→Asn; (HBB: c.399A>T)]: a mosaic to be put together

OBJECTIVES

Artifactually altered glycated hemoglobin (HbA_1c) concentrations are frequently linked to hemoglobin (Hb) variants. Their expression and detection require in-depth analysis.

METHODS

Cation exchange high performance liquid chromatography (HPLC) (Bio-Rad Variant™ II; Trinity Biotech Premier Hb9210 Resolution), capillary electrophoresis (CE) (Sebia Capillarys 2 Flex Piercing) and mass spectrometry (MS) (Waters) were used for variant detection; Sanger sequencing, multiplex ligation-dependent probe amplification (MLPA) and next generation sequencing (NGS) were used for DNA analysis; HbA_1c was measured with cation exchange HPLC (Bio-Rad Variant™ II; Arkray Adams HA-8180V; Tosoh HLC-723 G7), CE (Sebia Capillarys 2 Flex Piercing), boronate affinity HPLC (Trinity Biotech Hb9210 Premier), immunoassay (Cobas c501 Tina-quant HbA_1c Gen. 3; Nihon Kohden CHM-4100 Celltac chemi HbA_1c HA-411V) and enzymatic assay (Abbott Architect c 8000 HbA_1c).

RESULTS

Hb Yamagata [β132(H10)Lys→Asn; (HBB: c.399A>T)] was identified in the proband by MS after the observation of an abnormal peak in HPLC and CE. A mosaic expression of this variant was detected by NGS (mutant: 8%; wild type: 92%), after negative results in Sanger sequencing. Hb Yamagata interfered with HbA_1c measurements by cation exchange HPLC and CE whereas immuno and enzymatic assay values showed good agreement with boronate affinity HPLC measurement.

CONCLUSIONS

A mosaicism of Hb Yamagata was found in a patient with altered HbA_1c values. This rare gene variant was detected only by advanced technologies as MS and NGS. The variant interfered with common HbA_1c determination methods.

Unexpected HbA1c results in the presence of three rare hemoglobin variants

Hemoglobin (Hb) variants, characterized by structural abnormalities in the globin chains, are among the most common inherited disorders. It has been shown that Hb variant remains an important cause of erroneous HbA_1c results. Thus, it is important to be aware of the extent of the interference of each Hb variant encountered to avoid reporting unreliable results. However, the effects of many types of Hb variants on the measurement of HbA_1c remain unclear. Here, we describe three rare Hb variants, Hb J-Tashikuergan [HBA2: c.59 C > A], Hb Pyrgos [HBB: c.251G > A], and Hb Hope [HBB: c.410 G > A], which lead to extremely high values (>25%) determined by Variant II Turbo 2.0. We further investigated their effects on HbA_1c measurement by an HPLC system (Bio-Rad D100), a CE system (Sebia Capillarys 3 TERA), a boronate affinity chromatography system (Premier Hb9210), and an immunoassay method (Roche Diagnostics), and found that these Hb variants severely interfered with HbA_1c measurement by Variant II Turbo 2.0 and Bio-Rad D100. This study demonstrates that patients with abnormally high HbA_1c levels should be highly suspected of carrying Hb variants. When the HbA_1c results are considered unreliable, other indicators such as glycated albumin may be a possible alternative to HbA_1c in diabetic patients.

Hemoglobin variants in southern China: results obtained during the measurement of glycated hemoglobin in a large population

Objectives

Hemoglobin (Hb) variant is one of the most common monogenic inherited disorders. We aimed to explore the prevalence and hematological and molecular characteristics of Hb variants in southern China.

Methods

We collected blood samples from all patients with suspected variants found during HbA1c measurement via a cation-exchange high-performance liquid chromatography system (Bio-Rad Variant II Turbo 2.0) or a capillary electrophoresis method (Sebia Capillarys). Hematological analysis, Sanger sequencing, and gap-PCR were performed for these samples.

Results

Among the 311,024 patients tested, we found 1,074 Hb variant carriers, including 823 identified using Capillarys and 251 using Variant II Turbo 2.0, with a total carrier rate of 0.35%. We discovered 117 types of Hb variants (52 HBB, 47 HBA, and 18 HBD mutations) containing 18 new mutations. The most common variant found was Hb E, followed by Hb New York, Hb J-Bangkok, Hb Q-Thailand, Hb G-Coushatta, Hb G-Honolulu, Hb G-Taipei, and Hb Broomhill. Most heterozygotes for the Hb variant exhibited normal hematological parameters. However, most patients with compound heterozygotes for the Hb variant and thalassemia showed varied degrees of microcytic hypochromic anemia.

Conclusions

The prevalence of hemoglobin variants remains high and exhibits genetic diversity and widespread distribution in the population of southern China.

Impact of Rare and Common Genetic Variants on Diabetes Diagnosis by Hemoglobin A1c in Multi-Ancestry Cohorts: The Trans-Omics for Precision Medicine Program

Hemoglobin A1c (HbA1c) is widely used to diagnose diabetes and assess glycemic control in individuals with diabetes. However, nonglycemic determinants, including genetic variation, may influence how accurately HbA1c reflects underlying glycemia. Analyzing the NHLBI Trans-Omics for Precision Medicine (TOPMed) sequence data in 10,338 individuals from five studies and four ancestries (6,158 Europeans, 3,123 African-Americans, 650 Hispanics, and 407 East Asians), we confirmed five regions associated with HbA1c (GCK in Europeans and African-Americans, HK1 in Europeans and Hispanics, FN3K and/or FN3KRP in Europeans, and G6PD in African-Americans and Hispanics) and we identified an African-ancestry-specific low-frequency variant (rs1039215 in HBG2 and HBE1, minor allele frequency (MAF) = 0.03). The most associated G6PD variant (rs1050828-T, p.Val98Met, MAF = 12% in African-Americans, MAF = 2% in Hispanics) lowered HbA1c (-0.88% in hemizygous males, -0.34% in heterozygous females) and explained 23% of HbA1c variance in African-Americans and 4% in Hispanics. Additionally, we identified a rare distinct G6PD coding variant (rs76723693, p.Leu353Pro, MAF = 0.5%; -0.98% in hemizygous males, -0.46% in heterozygous females) and detected significant association with HbA1c when aggregating rare missense variants in G6PD. We observed similar magnitude and direction of effects for rs1039215 (HBG2) and rs76723693 (G6PD) in the two largest TOPMed African American cohorts, and we replicated the rs76723693 association in the UK Biobank African-ancestry participants. These variants in G6PD and HBG2 were monomorphic in the European and Asian samples. African or Hispanic ancestry individuals carrying G6PD variants may be underdiagnosed for diabetes when screened with HbA1c. Thus, assessment of these variants should be considered for incorporation into precision medicine approaches for diabetes diagnosis.

Hb Sichuan [α67(E16)Thr→Ile, HBA2: c.203C>T]: A Novel Hemoglobin Variant That Can Be Detected by Glycated Hemoglobin Electrophoresis

We report a novel α2-globin chain hemoglobin (Hb) variant in a 23-year-old female of Chinese Han nationality. The Hb variant can be detected by glycated Hb electrophoresis (CapillaryS2, Hb A_1c program). However, Hb fractions analyzed by capillary electrophoresis (CE) (CapillaryS2, Hb program) and high performance liquid chromatography (HPLC), (VARIANT II™ β-Thalassemia Short Program) showed no suspicious Hb variant. Sanger sequencing revealed a novel mutation [α67(E16)Thr→Ile, HBA2: c.203C>T]. We named this novel variant Hb Sichuan after the geographic origin of the proband.