Haemoglobin Hope: A Rare Hb Variant Causing Spuriously Elevated HbA1c Values on HPLC Assay

Abstract

Introduction: Hb Hope is a clinically asymptomatic β-chain variant [beta136 (H14) Gly→Asp (GGT→GAT)]. It is more prevalent in Mediterranean region of the world than in Asian countries and extremely rare in India. Aim:To evaluate the interference of clinically silent and extremely rare variant; haemoglobin Hope (Hb Hope) on the final reported value of glycated haemoglobin (HbA1c) by high performance liquid chromatography (HPLC). Materials and Methods:Eight EDTA blood samples showed very high values of HbA1c (>50 gm%) when processed by Bio-Rad Variant II turbo (HPLC). These were further processed for by capillary electrophoresis to look for the abnormal haemoglobin. Glycated Hb was also measured by immunoturbidimetry.Results: On HPLC, single abnormally high peak was observed for all the samples in the chromatogram leading to very high glycated haemoglobin values while in immunoturbidimetric assay reportable values were obtained. Moreover, capillary electrophoresis showed the presence of haemoglobin Hope in all the samples. Conclusion:Hb hope might lead to overestimation and possible misinterpretation of glycated haemoglobin results. Hb Hope is extremely rare in India but the possibility of interference by such clinically silent variant should always be kept in mind while interpreting the HbA1c values. INTRODUCTIONGlycated haemogobin (HbA1c) is a result of non-enzymatic glycation of hemoglobin with plasma glucose and is known to be clinically important in identifying the average plasma glucose concentration over periods of time. HbA1c is a measure of the beta-N-1-deoxy fructosyl component of haemoglobin. The extent of glycation and the relative involvement of β chains of haemoglobin remain unclear [1, 2]. HbA1c is expressed as the percentage of total haemoglobin which is 50% higher than HbA1c alone. Depending on the method used for estimating, the level of HbA1c is approximately 4-6% in healthy patients without diabetes. In clinical practice, the measurement of HbA1c serves as the marker the glycaemic control over the last three months and to determine whether the patient's blood glucose levels have remained within the target range [3]. Various methods and techniques such as high performance liquid chromatography (HPLC), immunoagglutination, boronate affinity assays, and electrophoresis have been developed based on different principles to measure HbA1C clinically but the designated DCCT comparison method is a cation exchange HPLC [4,5]. Despite advances in the measurement of glycated haemoglobin, an increasing number of hemoglobinopathies have been reported to cause falsely elevated or falsely low HbA1c results [3].Hb Hope is a clinically asymptomatic [beta136 (H14) Gly→Asp (GGT→GAT)] unstable variant of the β-globin chain that is frequently found in the Thai population [6]. It is extremely rare in India. We report the interference of Hb Hope with glycated haemoglobin values in South India. MATERIALS AND METHODSIt is a clinical study conducted in Department of Biochemistry, Kasturba Hospital, Manipal from A...

Dealing with Rare Beta Chain Hb Variants – Diagnostic Dilemmas

“…This salt bridge neutralizes the positive charges to the extent that HbA1c and Hb Hope co-elute from the HPLC column. So Hb Hope and HbA1c elute in the same window leading to probable overestimation [3]. Accidental discovery of this abnormal hemoglobin emphasizes the importance of testing glycated haemoglobin by several methods whenever very high values are obtained which are not in line with the blood glucose levels of the patient.…”

“…Dealing with Rare Beta Chain Hb Variants Annals of Pathology and Laboratory Medicine, Vol. 11, Issue 2, February 2024 haemoglobin variants [1]. We bring forth two cases of probable Hb Hope peaks eluted in zone 10 of the electrophoretogram assayed on capillary electrophoresis ( Sebia Capillarys Octa 3) and also show the comparative peaks on HPLC on same patients.…”

“…Hb Hope is one of the 700 haemoglobin variants identified till date that is clinically silent or is a silent variant that does not present with any clinical symptoms usually [1]. Capillary electrophoresis has the ability to completely separate and identify the…”