Fructosamine andHemoglobin A1C (bHA1C)

Dr. Yousef Elshrek

What is fructosamine• Fructosamine is one of the blood tests that can

be carried out to measure the blood glucose levels of people who have diabetes.

• Many people with this disease check their blood glucose levels daily with a home blood sugar meter.

• Glucose levels can fluctuate throughout the day, however, and doctors frequently wish to know the overall levels of this sugar in the blood.

• Usually, glucose control is monitored by the hemoglobin A1c test, which determines the blood sugar levels over the past three months.

• The fructosamine test is an alternate test that determines glucose levels over the previous 2-3 weeks.

• The common symptom of different types of diabetes mellitus is excessive levels of the sugar glucose in the blood.

• Over time, high levels of sugar can severely damage the kidneys, eyes, feet, and cardiovascular system.

• Therefore, diabetes is treated aggressively, frequently with medication.

• To determine how well the treatment schedule is working, patients generally check their blood sugar levels at least once a day with a blood sugar meter.

• It may appear that the levels of glucose are at their ideal levels, but levels may change wildly over the course of the day.

• To get a more accurate measurement of the glucose levels over time, doctors frequently perform blood tests to assess the average level of glucose over a period of time.

• There are two lab tests commonly performed to check blood glucose levels:1. The hemoglobin A1C test 2. The fructosamine test.

•Both measure the amount of glucose that has bound to proteins in the blood, known a glycated proteins.

The formation of Fructosamine• Fructosamine can be formed by as follows:-• Formation of Amadori product:- It is an intermediate in

the production of an advanced glycation end-product (AGE) as a result of glycation, the formation of an AGE involves the following steps:

1. Advanced glycation end products (AGEs)2. Advanced glycation end products (AGEs) are

modifications of proteins or lipids that become nonenzymatically glycated and oxidized after contact with aldose sugars.

• In other words, they are the result of a chain of chemical reactions which follow an initial glycation reaction.

• The intermediate products are known as Schiff base, Amadori, and Maillard products, after the researchers who first described them.

• Initially, glycation involves covalent reactions between free amino groups of amino acids, such as lysine, arginine, or protein terminal amino acids and sugars (glucose, fructose, ribose, etc), to create the following reactions

• first, the Schiff base and then Amadori products, of which the best known are HbA1c (Figure 1) and fructosamine (fructoselysine).

• Additional reactions occur successively

• Fig. 1 : The initial step of the Maillard reaction between glucose and an amino acid (RNH2), in which R is the amino acid side group

Figure 2. Formation of glycated hemoglobin A1c (HbA1c). HbA1c is an Amadori product and is formed through the intermediate Schiff base step.

• AGE formation from fructoselysine involves the nonoxidative dissociation of fructoselysine to form new reactive intermediates that again modify proteins to form AGEs of various different chemical structures (Figure 3).

• Alternatively, fructoselysine decays and releases its carbohydrate moiety either as glucose or as the more reactive hexoses, such as 3-deoxyglucosone, which themselves may modify proteins.

• In addition, it has recently been found that glucose can auto-oxidize to form reactive carbonyl compounds (glyoxal and methylglyoxal) which can react with proteins to form glycoxidation products .

• In addition to this, products of oxidative stress, such as peroxynitrite, can also induce the formation of carboxymethyl lysine by oxidative cleavage of Amadori products and/or the generation of reactive dicarbonyl compounds from glucose (Figure 2 and 3).

• Thus, AGEs can arise from glucose and lipids through several, partially intermingling reactions.

• Once formed, they may damage cellular structures via a number of mechanisms, including the formation of cross-links between key molecules in the basement membrane of the extracellular matrix (ECM) and the interaction of AGEs with RAGEs on cell surfaces, thus altering cellular functions.

Fig (3)Schematic representation of the formation of some common advanced glycation end products (AGEs).

• Accumulation of AGEs in the ECM occurs on proteins with a slow turnover rate, with the formation of cross-links that can trap other local macromolecules.• In this way, AGEs alter the properties of the

large matrix proteins collagen, vitronectin, and laminin. AGE cross-linking on type I collagen and elastin causes an increase in the area of ECM, resulting in increased stiffness of the vasculature.

• Glycation results in increased synthesis of type III collagen, type V collagen, type VI collagen, laminin, and fibronectin in the ECM, most likely via upregulation of transforming growth factor-â pathways. Formation of AGEs on laminin results in reduced binding to type IV collagen, reduced polymer elongation, and lower binding of heparan sulfate proteoglycan.

• Glycation of laminin and type I and type IV collagens, key molecules in the basement membrane, causes inhibited adhesion to endothelial cells for both matrix glycoproteins.

• In addition, it has been suggested that AGE formation leads to a reduction in the binding of collagen and heparan to the adhesive matrix molecule vitronectin.

• AGE-induced alterations of vitronectin and laminin may explain the reduction in binding of heparan sulfate proteoglycan, a stimulant of other matrix molecules in the vessel wall, to the diabetic basement membrane.

• As for the role of lipids, glycated low-density lipoprotein (LDL) reduces nitric oxide (NO) production and suppresses uptake and clearance of LDL through its receptor on endothelial cells.

Fig (1) Formation of fructosamine

• The amount of these proteins is much higher in people that have poor control of their diabetes.

• Many factors affect the amount of free glucose in the blood, but changes in the levels of glycated proteins happen much more slowly and give much more reproducible readings.

• The measurement of fructosamine detects the reaction product of glucose that has bound to the accessible amino group on a protein such as albumin, for example, giving glycated albumin.• Albumin has a circulating half life of

approximately 17 days, compared to 120 days for HbA1c. • Fructosamine is considered to be an

intermediate indicator of diabetic control because it is not as immediate as blood glucose, but not as longstanding as HbA1c.

• In general, fructosamine levels reflect glycemic control over the previous 2 to 3 weeks

• This test measures glucose levels over the last 2-3 weeks.

• It is an alternative to the more common hemoglobin a1c test, which can give false readings for patients with blood problems such as hemolytic or sickle cell anemia

• Additional reasons to use this alternate method of hematology include the need to measure blood sugar levels during pregnancy.• Because of the mother’s hormonal changes,

women with gestational diabetes can have rapid changes in their blood sugar. • Doctors wish to monitor these changes much

more frequently than with the three month period afforded by the standard test. • With the fructosamine test, they check blood

sugar levels for the past 2-3 weeks.

• Patients frequently undergo changes in their medication. • Their blood sugar levels may need to be checked frequently to

determine the effect of these changes. • The fructosamine test is better suited than the glycated

hemoglobin test to measure the rapidly changing glucose levels of such patients.

• It is more important to look at trends when evaluating fructosamine levels than it is to analyze the absolute percentage.

• Levels that decrease suggest that glucose levels are being brought under better control.

• Increasing levels suggest the opposite. • This test is not useful for screening for diabetes. • At the lower limit of the test, it is not clear whether a patient has

good diabetic control or whether they are free of the disease.

• Fructosamine is most useful when measurement of HbA1c is unreliable due to a hemoglobinopathy or hemolysis. • Fructosamine values are not accurate in

individuals with serum albumin levels below 3 g/dL or when serum albumin turnover is accelerated.• Examples include cirrhosis, nephrotic syndrome,

thyroid disease and paraproteinemia.• Reference range is 200 – 285 umol/L.

What is glycated protein• Several authors are improperly using the terms

“glucosylated (or glycosylated) hemoglobin”, 'protein glucosylation (or glycosylation)', etc. to refer to the products of nonenzymic reactions between glucose or other sugars and free amino groups of proteins.

• The compounds so formed are not glycosides, however, but result from the formation of a Schiff's base followed by an Amadori rearrangement.

• For example, the product of the reaction between glucose and hemoglobin is not glucosylated hemoglobin but an amino linked 1-deoxyfructose derivative of hemoglobin.

• The term 'glycation' for any reaction that links a sugar to a protein, whether it is catalyzed by an enzyme or not.

• The product of glycation is a glycated protein, or, in the particular case of the reaction with hemoglobin, glycated hemoglobin.

• Glycosylated Hemoglobin or Hemoglobin A1C (bHA1C)• Reflects average blood sugar levels over the preceding 90-

day period.• Elevated levels are associated with prediabetes and

diabetes.• Individuals with diabetes have an increased risk of a

cardiac event.• A diabetic person's risk for heart attack is the same as a

non-diabetic person, who has experienced one heart attack, having a second heart attack.

• Aggressive global preventive risk reduction efforts, such as lower LDL targets, diet, exercise and blood pressure control, are recommended.

• Goal values (per American Diabetes Association guidelines):

• A range of 5.7-6.4 percent indicates an increased risk for development of diabetes (i.e., prediabetes), and lifestyle interventions may be beneficial.

• A value equal or greater than 6.5 percent is considered diabetic.

• This test may be measured any time of the day without fasting.

• Glycosylated hemoglobin is blood glucose attached to hemoglobin (a component of blood). This test is often called the "diabetic report card." It reflects the average blood sugar for the two to three month period before the test.

• To calculate the average blood glucose level from the HbA1C:

• HbA1C level x (multiplied by) 33.3 – 86 = average blood glucose level for the past 90 days.

• HbA1C can be helpful to track diabetic control over time.

• e.g. If Some one has HgA1c is 6.6?.• HgA1c is 6.6 is not bad• A 6% is an average of 126. • If some has HgA1c is 7% is an average of 154 so

yours is some where in between or approx. 142-3. • The formula to convert A1c to BS is:• = 28.7 x A1c – 46.7. • Thus, an A1c of 7% = ( 28.7x7.0) – ( 46.7) = 154

HbA1c targets• For most people with diabetes, the HbA1c target is below

48 mmol /mol , since evidence shows that this can reduce the risk of developing diabetic complications, such as nerve damage, eye disease, kidney disease and heart disease.

• Individuals at risk of severe hypoglycaemia should aim for an HbA1c of less than 58 mmol /mol.

• However, any reduction in HbA1c levels (and therefore, any improvement in control), is still considered to have beneficial effects on the onset and progression of complications

HbA1c results

• You will now be getting used to seeing your HbA1c results reported using the IFCC (International Federation of Clinical Chemistry) reference measurement procedure of mmol/mol.

• A rough guide to the equivalent values can be found in the following conversion table

• To calculate the average blood glucose level from the HbA1C for past 90 days: • HbA1c level x (multiplied by) 33.3 – 86 =

average blood glucose level for the past 90 days. • HbA1c level = 0.017x Fructosamine +

1.61• Fructosamine = HbA1c- 1.61 ) X 58.82• HbA1C and Fructosamine can be helpful

to track diabetic control over time.

(%) (mmol/ mol)6.0 426.5 487.0 537.5 588.0 649.0 75

Table (1) Conversion of Hg A1c to mmol/ mol