HbA1C: Description, Diagnostic use, contraindication and interpretation
HbA1c description
Glycated haemoglobin (hemoglobin A1c or HbA1c) is a form of
hemoglobin which is formed by non-enzymatic glycation pathway when hemoglobin
is exposed to plasma glucose. HbA1c is defined as haemoglobin which is
irreversibly glycated at one or both N-terminal valines of the beta chains of
HbA1c. The haemoglobin molecule is glycated and continues to remain in the red
blood cell for the rest of its life-span (120 days) of RBC[1].
Normal range:
Healthy < 6.3 % HbA1c
Controlled 6.3-8.0%
HbA1c diagnostic use
HbA1c determination is important diagnostic investigation for
diabetes mellitus diagnosis, as well as it is used in monitoring of dietary control and
therapeutic policy during the treatment of diabetes where the effective control
of blood glucose levels is important in the prevention of ketosis and
hyperglycemia, and decreases severity of late diabetic complications such as
retinopathy, neuropathy, nephropathy, and cardiac disease [3].
HbA1c blood specimen
K2-EDTA or
NH4-heparinized whole blood.
HbA1c determination methods
1.
Haemoglobin
A1c Chromatography of normal adult blood divides in two parts: HbA 92-94%. HbA1 (6-8%) in which the B chain has an additional glucose group [2].
2. Cation exchange, high performance liquid chromatography (HPLC) to
separate HbA1c from other haemoglobin fractions. A
hemolyzed preparation of the whole blood is mixed continuously for 5 minutes
with a weak binding cation-exchange resin.
During this time, HbA binds to the resin. HbA consist of all the
other hemoglobins except A1c which remains in solution. After the mixing
period, a filter is used to separate the supernatant containing the A1c from
the resin. The percent glycohemoglobin is determined by measuring the
absorbance at 415 nm of the A1c fraction and the total hemoglobin fraction. The
ratio of the two absorbances gives the percent of HbA1c [4].
2.
The
HbA1c usually measured by isoelectric focusing or electrophoresis [2].
HbA1c contraindication
RBC lifespan is 120 days and 50%
of glycation occurs in 90-120 days. Therefore, some RBCs disorders result in
shortened RBCs life span and defect in glycation [5]. HbA1c is not good indicator for diabetic control in following cases:
Ø Blood loss.
Ø Haemolysis.
Ø Haemoglobinopathies and red cell disorders [1].
References
1. Gupta S et al. (2017) Laboratory Diagnosis of HbA1c: A Review. J
Nanomed Res 5(4):00120.
2. Koval D et al. (2011) Analysis of glycated hemoglobin A1c by
capillary electrophoresis and capillary isoelectric focusing. Anal Biochem
413(1): 8-15.
3. Niederau CM et al. (1998) Glycohemoglobins In: Thomas L, ed.
Clinical Laboratory Diagnostics. Use and assessment of clinical laboratory
results. Frankfurt/Main:TH-Books Verlagsgesellschaft mbH: 142-148.
4. NCCLS Document (1999), “Procedures for the collection of
arterial blood specimens”, Approved Standard, 3rd Ed.
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