Hemoglobin Himeji and inconsistent hemoglobin A1c values: a case report

An incidental finding of a hemoglobin E variant in a diabetic patient with an abnormal glycated hemoglobin level: a case report

BACKGROUND

Glycated hemoglobin is a well-known marker for evaluating long-term glycemic control. However, the accuracy of glycated hemoglobin measurement can be affected by the presence of hemoglobin variants, which makes the determination and interpretation of glycated hemoglobin values in terms of glycemic control not only difficult but also misleading. Here we present the first ever case of a patient with type 2 diabetes with hemoglobin E from Nepal, diagnosed incidentally because of spurious glycated hemoglobin levels.

CASE PRESENTATION

A 45-year-old Hindu Mongolian female with a history of type 2 diabetes for around 9 years but not very compliant with follow-ups was referred to our facility for plasma fasting and postprandial blood glucose levels and glycated hemoglobin. Fasting and postprandial blood sugars were found to be high. A consistent very low glycated hemoglobin by two different high-performance liquid chromatography (HPLC) methods compelled us to call the patient for a detailed clinical history and for the records of investigations done in the past. The patient has been a known case of type 2 diabetes for around 9 years and presented irregularly for follow-up visits. Around 4 years ago, she presented to a healthcare facility with fatigue, severe headaches, pain in the abdomen, discomfort, and dizziness for a couple of months, where she was shown to have high blood glucose. She was referred to a tertiary-level hospital in Kathmandu, where she was prescribed metformin 500 mg once daily (OD). Due to her abnormal hemoglobin A1c reports, she was then sent to the National Public Health Laboratory for repeat investigations. Her blood and urine investigations were sent. Complete blood count findings revealed high red blood cell and white blood cell counts, a low mean corpuscular volume, and a high red cell distribution width-coefficient of variation. Other parameters, including serum electrolytes, renal function tests, liver function tests, and urine routine examinations, were within normal limits. A peripheral blood smear revealed microcytic hypochromic red cells with some target cells. Hemoglobin electrophoresis showed a very high percentage of hemoglobin E, a very low percentage of hemoglobin A2, and normal proportions of hemoglobin A and hemoglobin F. A diagnosis of homozygous hemoglobin E was made, and family screening was advised.

CONCLUSIONS

Clinicians should be aware of the limitations of glycated hemoglobin estimation by ion exchange high-performance liquid chromatography in patients with hemoglobin E and other hemoglobin variants. If the clinical impression and glycated hemoglobin test results do not match, glycated hemoglobin values should be determined with a second method based on a different principle, and glycemic status should be confirmed through alternative investigations, preferably those that are not influenced by the presence of hemoglobin variants (for example, boronate affinity chromatography, fructosamine test, glycated albumin test, the oral glucose tolerance test, continuous glucose monitoring, etc.). Consistent or even doubtful results should also raise the suspicion of a hemoglobin variant, which should be confirmed through further evaluation and investigations.

The First Case of Hemoglobin J-Guantanamo Reported During HbA1c Measurement by High-Performance Liquid Chromatography at Moroccan Military Hospital Mohammed V

We present a 57-year-old woman with diabetes mellitus and no other known comorbidities. HbA1c measurement by high-performance liquid chromatography (HPLC) gave unquantified results and a supernumerary peak was detected on the chromatogram. A thorough exploration of the hemoglobin profile showed the presence of an unclassified variant. Alkaline pH capillary electrophoresis revealed the presence of an abnormal peak migrating at zone 11, comprising 40.1% of total hemoglobin. An abnormal band migrating between hemoglobin A and hemoglobin F was observed by acid gel electrophoresis. Sequencing of the β-globin gene confirmed the presence of a rare hemoglobin variant, hemoglobin J-Guantanamo (HBB:c.386C>A) in the heterozygous state, which was for the first time documented in Morocco. Through this report, we emphasize the importance of careful analysis of the HPLC chromatogram for the detection of possible hemoglobin variants in HbA1c measurement.

Diagnosis of Hemoglobinopathy and β-Thalassemia by 21 Tesla Fourier Transform Ion Cyclotron Resonance Mass Spectrometry and Tandem Mass Spectrometry of Hemoglobin from Blood

BACKGROUND

Hemoglobinopathies and thalassemias are the most common genetically determined disorders. Current screening methods include cation-exchange HPLC and electrophoresis, the results of which can be ambiguous because of limited resolving power. Subsequently, laborious genetic testing is required for confirmation.

METHODS

We performed a top-down tandem mass spectrometry (MS/MS) approach with a fast data acquisition (3 min), ultrahigh mass accuracy, and extensive residue cleavage by use of positive electrospray ionization 21 Tesla Fourier transform ion cyclotron resonance-tandem mass spectrometry (21 T FT-ICR MS/MS) for hemoglobin (Hb) variant de novo sequencing and β-thalassemia diagnosis.

RESULTS

We correctly identified all Hb variants in blind analysis of 18 samples, including the first characterization of homozygous Hb Himeji variant. In addition, an Hb heterozygous variant with isotopologue mass spacing as small as 0.0194 Da (Hb AD) was resolved in both precursor ion mass spectrum (MS1) and product ion mass spectrum (MS2). In blind analysis, we also observed that the abundance ratio between intact δ and β subunits (δ/β) or the abundance ratio between intact δ and α subunits (δ/α) could serve to diagnose β-thalassemia trait caused by a mutation in 1 HBB gene.

CONCLUSIONS

We found that 21 T FT-ICR MS/MS provides a benchmark for top-down MS/MS analysis of blood Hb. The present method has the potential to be translated to lower resolving power mass spectrometers (lower field FT-ICR mass spectrometry and Orbitrap) for Hb variant analysis (by MS1 and MS2) and β-thalassemia diagnosis (MS1).