HbJ Bangkok: a single variant causing diagnostic confusion in bA1cmeasurement for beta-thalassemia trait
HbJ variant interference in HbA1c
Authors
Abstract
Introduction Glycated haemoglobin (HbA1c) is an essential biomarker for assessing glycaemic control in diabetes mellitus. However, haemoglobin variants can interfere with the accuracy of HbA1c measurements.
Case Presentation This case describes a 34-year-old man with beta-thalassemia trait in whom standard HbA1c testing gave misleading results. Despite normal glucose and insulin levels, HbA1c testing by HPLC revealed an unexpectedly low value of 3.1%, which was confirmed on reanalysis. Further testing identified the Hb J Bangkok variant, which was confirmed by genetic testing.
Conclusion This case highlights the importance of considering haemoglobin variants such as Hb J Bangkok when interpreting HbA1c results, as these variants can lead to significant discrepancies in glycaemic assessment and misdiagnosis. In such scenarios, comprehensive genetic evaluation is essential to ensure accurate diagnosis and appropriate patient management.
Keywords
Introduction
Glycated hemoglobin (HbA1c) is a widely used biomarker for monitoring long-term glycemic control in patients with diabetes mellitus. It reflects the average blood glucose levels over a period of approximately three months and is a cornerstone in the diagnosis and management of diabetes. However, the accuracy of HbA1c measurements can be significantly affected by various factors, including the presence of hemoglobin variants. Hemoglobin variants are genetic alterations that can lead to structural changes in the hemoglobin molecule, thereby interfering with HbA1c assays and leading to misleading results 1.
One such variant is Hb J Bangkok, a rare hemoglobinopathy characterized by a substitution in the beta-globin chain. This variant, like others, can produce aberrant results in HbA1c measurements, posing a challenge for accurate glycemic assessment. In patients with hemoglobin variants, HbA1c results may be artificially low or high, depending on the specific assay used, which can complicate the clinical interpretation of glycemic control 2.
The identification of hemoglobin variants such as Hb J Bangkok is crucial, especially in patients who do not have a known history of diabetes but present with unexpected HbA1c results. In such cases, reliance on HbA1c alone for evaluating glycemic control may lead to incorrect diagnoses and inappropriate management strategies. Therefore, alternative markers such as fructosamine, which are not influenced by hemoglobin variants, should be considered. Additionally, genetic testing and hemoglobin electrophoresis are essential tools in diagnosing and understanding the clinical implications of these variants 3.
In this report, we describe a case of a 34-year-old male with no known history of diabetes who was found to have abnormally low HbA1c levels. Further investigation revealed the presence of the Hb J Bangkok variant, highlighting the diagnostic challenges associated with hemoglobinopathies and the need for alternative approaches in assessing glycemic control.
Materials and Methods
A 34-year-old male of Caucasian, residing in the Eastern Black Sea region, presented to the endocrinology clinic for routine evaluation due to a family history of diabetes in his mother. The patient had no known chronic medical conditions. Initial laboratory tests revealed normal fasting and postprandial blood glucose levels, as well as normal insulin levels. His fasting blood glucose was measured at 96 mg/dL, and postprandial blood glucose was 76 mg/dL. The total bilirubin levels, measured at one-month intervals, were 1.73 mg/dL and 1.58 mg/dL, respectively. However, the HbA1c test, performed using high-performance liquid chromatography (HPLC) on a Tosoh G8 analyzer, showed an unexpectedly low result of 3.1%. The internal quality control run of the instrumet was within normal limits. The patient’s sample was rechecked using the Arkray 8180T analyzer, yielding the same HbA1c value of 3.1%.
Given these findings, the patient was contacted and advised to undergo a complete blood count (CBC) and hemoglobin electrophoresis. A detailed medical history was obtained, and previous investigation records were reviewed, including family history. The patient’s family members were invited to the clinic for HbA1c testing. The father’s HbA1c was found to be 3.3%, and the sister’s HbA1c was 3.1%. Notably, the sister’s medical history revealed an HbA1c level of 6% one year prior with the same Tosoh G8 analyser. Patient’s hemoglobin electrophoresis performed, revealing a peak at Z12 (figure 1). Genetic testing was recommended to the patient and his family. While the sister declined testing, both the patient and his father consented to the test.
Although activated partial thromboplastin time (aPTT) and prothrombin time (PT) were normal, during blood sampling, clotting was observed in the patient’s sodium citrate coagulation tube, leading to the decision to also conduct a genetic thrombophilia panel. PCR-DNA sequencing of the beta-globin (HBB) gene, specifically the coding exons and exon-intron boundaries, revealed that the patient was heterozygous for the p.Gly.Asp (c.170G>A) variant in the HBB gene. This variant is classified as “likely benign” in the ClinVar database and as “uncertain significance” in the Franklin database. In the literature, this variant is associated with an abnormal hemoglobin variant known as Hb J Bangkok. Additionally, full gene sequencing of HBA1 & HBA2 for alpha-thalassemia did not detect any mutations. The patient’s peripheral blood sample was analyzed for SNP regions using Real-Time PCR on the ROCHE LightCycler480 device. The results were MTHFR c.677C>T heterozygous, PAI 4G/5G heterozygous, MTHFR c.1298A>C heterozygous, FXIII p.V34L heterozygous, Prothrombin g.20210G>A normal, and FV (Leiden) c.1691G>A (normal). All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.
Discussion
This case exemplifies the diagnostic challenges posed by hemoglobin variants in the context of HbA1c interpretation, particularly in patients without a known history of diabetes. The patient, a 34-year-old male with a family history of diabetes, presented with normal fasting and postprandial glucose levels but exhibited anomalously low HbA1c values across multiple assays. The discovery of the Hb J Bangkok variant through genetic testing underscores the critical need for clinicians to consider hemoglobinopathies when confronted with discordant HbA1c results4. The capillary hemoglobin electrophoresis results revealed a significant peak in the Z12 zone, which is indicative of an abnormal hemoglobin variant. This peak is strongly suggestive of Hb J Bangkok, a rare variant that is not typically present in a healthy individual’s hemoglobin profile. The prominence of the Z12 peak suggests that Hb J Bangkok constitutes a considerable portion of the patient’s hemoglobin, which could explain the interference with standard HbA1c assays and the resulting atypically low readings. In addition to the abnormal peak in the Z12 zone, the electropherogram also shows a distinct peak corresponding to Hb A, the major component of normal adult hemoglobin. The presence of a normal Hb A peak is crucial as it indicates that, despite the presence of the Hb J Bangkok variant, the patient retains a significant proportion of normal hemoglobin. This finding helps in differentiating the presence of a hemoglobin variant from other conditions such as thalassemia, where Hb A might be reduced. The electrophoresis also identified a smaller peak for Hb A2, which typically constitutes 2-3% of the total hemoglobin in a healthy individual. The normal range of Hb A2 observed in this patient further distinguishes the condition from beta-thalassemia, where Hb A2 levels are usually elevated. The absence of significant peaks in other zones, such as Z10 and Z11, further confirms that the major abnormal hemoglobin present is Hb J Bangkok. The capillary electrophoresis findings are therefore essential in understanding the patient’s unique hemoglobin composition and in guiding the clinical interpretation of laboratory results.
Hemoglobin variants, such as Hb J Bangkok, can significantly interfere with the accuracy of HbA1c measurements, leading to potential misinterpretations and inappropriate clinical decisions5,6. This interference arises because these variants can alter the structure of hemoglobin, affecting its behavior in assays designed to measure glycation levels. Consequently, reliance on HbA1c alone in such cases could obscure the true glycemic status of the patient, as evidenced by the consistently low HbA1c levels observed in this case despite normal glucose readings.
The findings in this case also highlight the importance of comprehensive genetic testing when confronted with unexpected laboratory results, especially in populations where hemoglobin variants may be more prevalent 7. The identification of the p.Gly.Asp (c.170G>A) variant in the HBB gene, known to be associated with Hb J Bangkok, was crucial in understanding the patient’s clinical presentation and in guiding further management. Additionally, the discovery of heterozygous mutations in genes associated with thrombophilia further complicates the clinical picture, indicating a potential need for ongoing monitoring and tailored therapeutic approaches8.
Limitations
This case report has several limitations. The observations from a single patient cannot be broadly applied to populations with hemoglobin variants or beta-thalassemia trait. Secondly, the interpretation of HbA1c interference was restricted due to the utilization of only two analytical platforms (Tosoh G8 and Arkray 8180T), and comparing additional assay methodologies might have yielded further insight into the degree of analytical variability. Thirdly, the presence of the Hb J Bangkok variant was confirmed by genetic testing; however, family members were not universally tested, thereby precluding a more extensive assessment of hereditary patterns. Ultimately, the assessment did not include alternative glycemic markers, such as fructosamine or continuous glucose monitoring, which could have provided further evidence of the patient’s actual glycemic state.
Declarations
Animal and Human Rights Statement
All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.
Data Availability
The datasets used and/or analyzed during the current study are not publicly available due to patient privacy reasons but are available from the corresponding author on reasonable request.
Conflict of Interest
The authors declare that there is no conflict of interest.
Funding
None.
Scientific Responsibility Statement
The authors declare that they are responsible for the article’s scientific content, including study design, data collection, analysis and interpretation, writing, and some of the main line, or all of the preparation and scientific review of the contents, and approval of the final version of the article.
Acknowledgements
The authors would like to express their sincere gratitude to the laboratory staff at Recep Tayyip Erdoğan University Training and Research Hospital for their invaluable assistance in the processing and analysis of the patient samples. During the course of preparing this work, the author(s) used ChatGPT for the purpose of refining the language. Following the use of this tool, the authors formally reviewed the content for its accuracy and edited it as necessary. The authors take full responsibility for all the content of this publication.
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How to Cite This Article
Hülya Kılıç, Bayram Şen, Şenol Çitli, Kübra Sönmez, Medeni Arpa. HbJ Bangkok: a single variant causing diagnostic confusion in HbA1c measurement for beta-thalassemia trait. Ann Clin Anal Med 2024; DOI: 10.4328/ACAM.22431
- Received:
- October 1, 2024
- Accepted:
- November 11, 2024
- Published Online:
- January 29, 2025