Glycated albumin and glycated hemoglobin- A comparison

The progressive complications of unmanaged diabetes include heart disease, blindness, kidney failure, amputation of extremities due to circulation problems, and nerve disorders, as well as other chronic conditions. The process of protein glycation is now understood to be both a marker for the progress of diabetes complications and an underlying cause of many of the most serious complications. Diabetes monitoring for protein glycation, an essential element for the long-term control of the complications of diabetes mellitus, is currently managed by a combination of daily self-monitoring of blood glucose (SMBG) measurements and physician-assessed hemoglobin A1c (A1C) levels every 3–6 months.


Introduction
The progressive complications of unmanaged diabetes include heart disease, blindness, kidney failure, amputation of extremities due to circulation problems, and nerve disorders, as well as other chronic conditions. 1,2,3 The process of protein glycation is now understood to be both a marker for the progress of diabetes complications and an underlying cause of many of the most serious complications. Diabetes monitoring for protein glycation, an essential element for the long-term control of the complications of diabetes mellitus, is currently managed by a combination of daily self-monitoring of blood glucose (SMBG) measurements and physician-assessed hemoglobin A1c (A1C) levels every 3-6 months. 4,5,6,7,8

Glycated Haemoglobin
A form of hemoglobin that is measured primarily to identify the average plasma glucose concentration over prolonged periods of time. It is formed in a non-enzymatic glycation pathway by hemoglobin's exposure to plasma glucose. Normal levels of glucose produce a normal amount of glycated hemoglobin. As the average amount of plasma glucose increases, the fraction of glycated hemoglobin increases in a predictable way. 9,10,11 In the normal ~120-day lifespan of the red blood cell, glucose molecules react with hemoglobin, forming glycated hemoglobin. Once a hemoglobin molecule is glycated, it remains that way. The HbA 1c level is proportional to average blood glucose concentration over the previous four weeks to three month. 12,13

Glycated Albumin
Human serum albumin is the most abundant protein in human blood plasma. It is produced in the liver. Albumin constitutes about half of the blood serum protein. It is soluble and monomeric. The reference range for albumin concentrations in blood is 3.4 to 5.4 g/dL. It has a serum half-life of approximately 20 days. It has a molecular mass of 67 kDa. Approximately 10% of the albumin in normal human serum is modified by nonenzymatic glycosylation, primarily at the epsilon-amino group of lysine residue 525. The amount of glycosylated albumin in serum is markedly elevated in diabetes and thus its determination may help in the monitoring of the disease. 14,15

Materials
Hospital's Ethical Committee clearance was obtained to carry out the study.
The patients for the study were selected from Medicine OPD, KIMS and were divided into three groups: • 25 healthy patients (non diabetic) were included as controls.
• 25 patients were included with diabetic history of more than five years and urine micral levels less than 20µg/ml.
• 25 patients were included with diabetic history of more than five years and urine microalbumin levels between 20-200µg/ml.
Inclusion criteria for the project was patient with DM >5 years and presence of hypercholeteremia (>250 mg/dl).
Exclusion criteria were patient with ESRD and participation in another clinical trial. HbA1c levels and Glycated Albumin levels were measured in all the three groups along with Fasting Glucose levels.

Methods
Fasting blood glucose levels were measured by Glucose Oxidase Peroxidase Method.
Urine Micral levels were measured by Immunoturbidimetric Method using latex coated anti albumin antibodies.
HbA1c levels were measured by High Performance Liquid Chromatography using D10 HbA1c Analyzer. Glycated Albumin was measured by enzymatic method (Lucica GA-L glycated albumin assay kit) using albumin specific protease, ketoamine oxidase and albumin assay reagent. GA was hydrolyzed to amino acids by albumin specific proteinase and then oxidized by ketoamine oxidase to produce hydrogen peroxide, which was measured quantitatively. The GA value was calculated as the percentage of GA relative to total albumin, which was measured with bromocresol purple method.

Discussion
The normal cut of value for GA was calculated using the control group and was found to be around 14%. GA was significantly higher in diabetic patients indicating its role in assessing glycemic control. Microalbuminuric patients had significantly higher GA levels (Normal Range-11 to 16%) than normoalbuminuric patients (p<0.05) indicating poor glycemic control patients are more likely to have diabetic complications. The increase in GA levels correlated with the increase in HbA1c levels (r=0.87), which proves GA can be used as an alternative glycemic indicator. Patients with microalbuminuria had higher % of hypertension compared with diabetic patients in whom microalbumin in urine was negative, signifying hypertension can be a factor for diabetic complications.
Microalbumin in urine was present in patient with longer diabetic history (around 10 years). This results correlated well with documentated evidence that diabetic nephropathy usually occur after 10-15 years after diagnosis of diabetes.

Conclusion
Glycated Albumin can be used as marker for glycemic control. As half life of albumin is significantly lower compared to life span of RBC, GA can be used as an intermediate glycemic indicator (every three to four weeks). Monthly assessment of GA in patients of Diabetes more than 5 years can prevent complications.