Glycosylated haemoglobin in the fetus: chemistry, laboratory measurements and future clinical implications

Development of filter paper hemoglobin A1c assay applicable to newborn screening

PURPOSE

Gestational diabetes influences risk for future metabolic disease including type 2 diabetes. Hemoglobin A1c (HbA1c) measurement assesses hemoglobin A glycosylation, and could theoretically be used as a test to estimate gestational glucose exposure. HbA1c assay on dried blood spots (DBS) is needed before potential application to statewide newborn screening (NBS) population studies. The study aimed to establish a reliable method to measure HbA1c on NBS DBS specimens. De-identified blood was used to generate trials to evaluate stability of HbA1c in DBS, optimal elution time, and stability of eluted blood.

RESULTS

Analysis of DBS stability HbA1c measurements from 3 to 6days after collection overestimated HbA1c values by a bias factor between 0.83 and 0.87. Sixty minutes of elution time produced maximal reproducibility and minimal bias of results. Within assay standard deviation: 0.058; average bias: -0.02%. Stability of eluted blood did not vary significantly between days 0-2 after DBS elution.

CONCLUSIONS

Measurement of HbA1c levels on DBS from human blood is feasible. Results suggest new method using DBS to measure HbA1c level with the following characteristics: optimal time for sample analysis 3-6days after collection, elution time of 60min and eluted blood analysis within 2days of elution. Measurement of neonatal HbA1c could provide insight regarding the infant's in utero exposure to glucose.

Fetal hemoglobin: assessment of glycation and acetylation status by electrospray ionization mass spectrometry

: Electrospray ionization mass spectrometry (ESI-MS) can be used for the measurement of glycated adult hemoglobin. Here, we describe the evaluation of ESI-MS for measurement of glycated (GHbF) and acetylated (AcHbF) fetal hemoglobin and the identification by mass of different chains of fetal hemoglobin.

: Blood samples were diluted in an acidic denaturing solvent, desalted with AG 50W-X8 resin and introduced directly into the mass spectrometer. Resulting mass spectra were processed to determine the percentage of GHbF and AcHbF and the γ-chain masses.

: The procedure yielded reproducible quantitative assay of GHbF and AcHbF, with coefficients of variation <4.9%. Measurement of α-chain glycation was similarly reproducible and is suggested as an alternative marker of glycemic control. Marked increases in glycation occurred in dried spot blood samples, which were related to duration of storage, temperature and glucose concentration. Molecular masses of fetal hemoglobin chains were also determined and in 42 neonates studied, two types A and B were identified, two-thirds were type A with γ-chain masses corresponding to

: ESI-MS can be used for the estimation of GHbF and AcHbF and the accurate measurement of fetal γ-chain masses. The use of whole blood is preferred for analysis.

Clin Chem Lab Med 2008;46:1230–8.

Derivated fetal haemoglobin as a marker for red cell age in the human fetus reflecting stimulated or impaired red blood cell production

We have determined whether derivated fetal haemoglobin (dHbF, consisting of glycated and acetylated HbF) can be used as a cell age marker for fetal red blood cells (RBCs). Cord blood was obtained between 19 and 39 weeks of gestation from 28 alloimmunised anaemic fetuses (23 RhD+ and 5 Kell) and from 20 non-anaemic fetuses and newborns (controls). Density gradient centrifugation was applied to 36 samples (20 RhD+, 15 controls and 1 Kell) to obtain fractions of increasing cell age. Blood samples were used for measurements of mean cellular volume (MCV), mean cell haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC), pyruvate kinase activity (PK) and derivated fetal haemoglobin (dHbF) by cation-exchange HPLC. Reticulocytes were counted only in the whole blood samples. In all density gradient separated RBC fractions, the values for MCV, MCH and PK activity decreased and those of MCHC and dHbF increased with increasing density (equivalent to increasing cell age). The mean density was lower for RBCs of the anaemic RHD group (1.072+/-0.007 g/ml) than for the non-anaemic controls (1.077+/-0.005 g/ml) (p<0.05) The RBC density of the Kell sensitised fetus did not differ from those of the controls. In the control group, the values of the cell age markers in whole blood changed significantly with the gestational age, showing an increase of mean age of the erythrocyte population. The best linear relationship was found for dHbF (y=6.28+0.17*weeks; r=0.84; p<0.001). In the anaemic RhD+ fetuses, the RBC age markers did not change with gestational age; the dHbF percentages were lower, and the MCV, MCH, PK values and the reticulocyte counts were higher than in the controls (0.05<p<0.001). The dHbF values of the Kell sensitised fetuses were above (p<0.01) and the reticulocyte counts were below normal (p<0.05) for gestational age. For the anaemic fetuses, a significant number of the dHbF values (86%) and of the reticulocyte counts (78%) differed from the values of the controls (p<0.01). The dHbF percentages in RhD+ fetuses showed the best correlation with the Hb deficit, which is a measure for anaemia (r=-0.81, p<0.0001). We conclude that the percentage derivated HbF may indicate whether the RBC production is normal for gestational age. It may in that sense reflect stimulated or impaired erythropoiesis in alloimmunised haemolytic anaemia.

Chromatographic and electrophoretic methods for modified hemoglobins

The discovery of the clinically important glycohemoglobin adducts and their relation to diabetes mellitus have greatly stimulated the study of other minor post-translational modifications of hemoglobin. Chromatographic and electrophoretic procedures have played an important role in these studies. Today several hemoglobin adducts are known and the formation of adducts with glucose, phosphorylated carbohydrates, urea/cyanate, aspirin, vitamins, acetaldehyde, penicillin and acetyl CoA have been described. Furthermore, new adducts, such as those observed using hemoglobin as a biochemical marker monitoring environmental, occupational and lifestyle exposures to reactive toxic chemicals are constantly being reported. This review deals with chromatographic and electrophoretic separation methods available for the study of non-enzymatic post-translational modifications of hemoglobin. Suitability, perspectives and biomedical applications are discussed.