Role of HbA1c in Role of HbA1c in Diabetes MellitusDiabetes Mellitus

Prof. S. ThakurProf. S. Thakur

Diabetes managementDiabetes management

Comprehensive and holisticComprehensive and holistic Defining, achieving, maintaining, Defining, achieving, maintaining,

and monitoring various targetsand monitoring various targets GlycemiaGlycemia HTNHTN DyslipidemiaDyslipidemia

Why glycemiaWhy glycemia

UKPDS/DCCT/Kemanoto studyUKPDS/DCCT/Kemanoto study

Assessment of Glycemic Assessment of Glycemic GoalsGoals

SMBGSMBG HbA1cHbA1c Glycated Protein (Fructosamine)Glycated Protein (Fructosamine) Continuous blood glucose Continuous blood glucose

monitoringmonitoring 1,5 anhydroglucitol (1,5 AG)1,5 anhydroglucitol (1,5 AG)

History of HbA1cHistory of HbA1c

S. Rahbar 1960 – description of S. Rahbar 1960 – description of abnormal Hb in DMabnormal Hb in DM

1970 – HbA1c increases in direct 1970 – HbA1c increases in direct proportion to hyperglycemiaproportion to hyperglycemia

Koenig RJ 1976 – periodic HbA1c Koenig RJ 1976 – periodic HbA1c monitoring indicates degree of monitoring indicates degree of controlcontrol

1980 – HbA1c available as method of 1980 – HbA1c available as method of glucose monitoringglucose monitoring

HbA1c – not fully integrated in HbA1c – not fully integrated in management of DM in Indiamanagement of DM in India 5.9% - tested at diagnosis5.9% - tested at diagnosis 7.6% - tested at diagnosis7.6% - tested at diagnosis

Mean HbA1cin India (8.9 +/- 2.1%)Mean HbA1cin India (8.9 +/- 2.1%) Other Asian Countries (8.6 +/- 2%)Other Asian Countries (8.6 +/- 2%) Significant higher HbA1c>2% above Significant higher HbA1c>2% above

normal in India. Chuang et al. Diabet normal in India. Chuang et al. Diabet Med. 2002.Med. 2002.

Diab care Asia 1998

Bjork et al;2003

TerminologyTerminology

HbA – unglycated hemoglobin.HbA – unglycated hemoglobin. GHb – Glycated HbGHb – Glycated Hb HbA1 – Carbohydrates bound to N terminal valine of B HbA1 – Carbohydrates bound to N terminal valine of B

chain.chain. HbA1a1 – Fructose 1-6 bisphospate ”HbA1a1 – Fructose 1-6 bisphospate ” HbA1a2 – Glucose – 6 – phosphate ”HbA1a2 – Glucose – 6 – phosphate ” HbA1b – Unknown carbohydrate residue ”HbA1b – Unknown carbohydrate residue ” HbA1c – Glucose bound to N terminal of valine of B HbA1c – Glucose bound to N terminal of valine of B

chainchain

Steps in glycationSteps in glycation

Non – enzymatic binding of glucose Non – enzymatic binding of glucose to various proteinsto various proteins

Maillard reactionMaillard reaction Freee amino group (Hb) = aldehyde Freee amino group (Hb) = aldehyde

group (glucose) group (glucose) shiff base shiff base (alamine labie form)(alamine labie form)

Alamine (shiff base) Alamine (shiff base) ketoamine (amadori rearrangement)ketoamine (amadori rearrangement)

Methods used for Methods used for determination of HbA1cdetermination of HbA1c

A1c Assay – percent of hemoglobin A1c Assay – percent of hemoglobin that is glycated that is glycated Boronate affinity chromographyBoronate affinity chromography Cation or ion exchange chromatography Cation or ion exchange chromatography

(HPLC, LPLC)(HPLC, LPLC) Immuno assay (turbidometry)Immuno assay (turbidometry) Agar gelelectrophoresisAgar gelelectrophoresis Mass spectroscopyMass spectroscopy Capillary electrophoresis.Capillary electrophoresis.

Confounders for Confounders for determination of HbA1cdetermination of HbA1c

When to suspectWhen to suspect HbA1c reading low or highHbA1c reading low or high Significant change in various methodsSignificant change in various methods

Types of confoundersTypes of confounders MethodologicalMethodological PhysiologicalPhysiological

Methodological Methodological confoundersconfounders

Hemoglobin variant and chemically Hemoglobin variant and chemically modified Hb (carbamylated and modified Hb (carbamylated and acetylated).acetylated).

Reduced RBC life spanReduced RBC life span Impact on reactivity N terminal Impact on reactivity N terminal

amino group B chainamino group B chain

Physiological Physiological confoundersconfounders

RBC kinetic – decreased RBC life span -RBC kinetic – decreased RBC life span -Decreased HbA1cDecreased HbA1c

Kidney, liver disease, hemolytic anemia, Kidney, liver disease, hemolytic anemia, hemoglobinopathies and recovery from blood hemoglobinopathies and recovery from blood loss.loss.

Decreased erythropoiesis – increased HbA1c – Decreased erythropoiesis – increased HbA1c – Aplastic anemia, Iron deff. Anemia.Aplastic anemia, Iron deff. Anemia.

Inhibition of glycation decreased HbA1c – Vit Inhibition of glycation decreased HbA1c – Vit C, Vit E.C, Vit E.

Pregnancy – HbA1c lower (decreased RBC life Pregnancy – HbA1c lower (decreased RBC life span, decreased Hb)span, decreased Hb)

Contribution of fasting and Contribution of fasting and PP sugar to HbA1cPP sugar to HbA1c

Relationship of HbA1c to Relationship of HbA1c to mean plasma glucose mean plasma glucose

(DCCT trial)(DCCT trial)A1cA1c Mean plasma glucose (mg/dl) Mean plasma glucose (mg/dl)

Mmol/lMmol/l

66 135135 7.57.5

77 170170 9.59.5

88 205205 11.511.5

99 240240 13.513.5

1010 275275 15.515.5

1111 310310 17.517.5

1212 345345 19.519.5

A1c derived average A1c derived average glucose (ADAG) – CAG glucose (ADAG) – CAG

(diabetes care Aug 2008)(diabetes care Aug 2008) eAG (mg/dl)= 28.7 x A1c – 46.7eAG (mg/dl)= 28.7 x A1c – 46.7 eAG (mmol/dl) = 1.5 A1c – 2.59eAG (mmol/dl) = 1.5 A1c – 2.59

A1c%A1c% mg/dlmg/dl mmol/lmmol/l

55 97 (76-120)97 (76-120) 5.4 (4.2 – 6.7)5.4 (4.2 – 6.7)

66 126 (100-152)126 (100-152) 7.0 (5.5 – 8.5)7.0 (5.5 – 8.5)

77 154 (123 – 185)154 (123 – 185) 8.6 (6.8 – 10.3)8.6 (6.8 – 10.3)

88 183 (147 – 217)183 (147 – 217) 10.2 (8.1-12.1)10.2 (8.1-12.1)

99 212 (170 – 249)212 (170 – 249) 11.8 (9.4 – 13.9)11.8 (9.4 – 13.9)

1010 240 (193 – 282)240 (193 – 282) 13.4 (10.7 – 15.7)13.4 (10.7 – 15.7)

1111 269 (217 – 314)269 (217 – 314) 14.9 (12.0 – 17.5)14.9 (12.0 – 17.5)

1212 298 (240 – 347)298 (240 – 347) 16.5 ( 13.3 – 19.3)16.5 ( 13.3 – 19.3)

Reference range of Reference range of HbA1cHbA1c

4-6% - NGSP, DCCT.4-6% - NGSP, DCCT. 2% - 4% - IFCC.2% - 4% - IFCC.

AIC Targets AIC Targets AIC TargetsAIC Targets Level of DiseaseLevel of Disease ADA - <7%ADA - <7% AA DAF - <6.5%DAF - <6.5% >6% ?>6% ? BB No single HbA1c that confer maximum No single HbA1c that confer maximum

benefitbenefit Targets individualized, balancing optimal Targets individualized, balancing optimal

control, safety, feasibility.control, safety, feasibility. Less stringent goals in – h/o hyperglycemic Less stringent goals in – h/o hyperglycemic

episodes, limited life expectancy in children, episodes, limited life expectancy in children, comorbidities, long standing DM with stable comorbidities, long standing DM with stable or minimal microvascular complications (E)or minimal microvascular complications (E)

Frequency of monitoring Frequency of monitoring HbA1cHbA1c

3 month 3 month unstable DMunstable DM change of treatmentchange of treatment

6 month 6 month stable DMstable DM

Pregnancy – more frequentPregnancy – more frequent

Clinical application of Clinical application of HbA1cHbA1c

Only indicated for monitoring, not Only indicated for monitoring, not diagnosis & screeningdiagnosis & screening

Curvilinear relationship between HbA1c Curvilinear relationship between HbA1c and microvascular complications( and microvascular complications( DCCT/EDIC/UKPDS/kumomoto study) DCCT/EDIC/UKPDS/kumomoto study)

Evidence for CVD reduction – only Evidence for CVD reduction – only epidemiological evidenceepidemiological evidence

Lowering AIc from 7% - 6% absolute risk Lowering AIc from 7% - 6% absolute risk reduction however smaller given reduction however smaller given increased risk of hypoglycemiaincreased risk of hypoglycemia

LimitationLimitation

Only for monitoring not diagnosis and Only for monitoring not diagnosis and screeningscreening

Hypoglycemic episodes not detectedHypoglycemic episodes not detected Variability not detectedVariability not detected Methodological and physiological confoundersMethodological and physiological confounders Lack of standardization/availability/costLack of standardization/availability/cost Weighted to most recent changeWeighted to most recent change

50% HbA1c – 30 days50% HbA1c – 30 days 25% HbA1c – 30-60 days25% HbA1c – 30-60 days 25% HbA1c – 60 – 120 days25% HbA1c – 60 – 120 days

Fructosamine vs. HbA1cFructosamine vs. HbA1c

Alternative or suppplement to Alternative or suppplement to HbA1c in glycemic controlHbA1c in glycemic control

Particularly in pregnancy or altered Particularly in pregnancy or altered RBC kineticsRBC kinetics

Unlike HbA1c Fructosamine has not Unlike HbA1c Fructosamine has not proven to be reliable and useful in proven to be reliable and useful in routine management of Diabetesroutine management of Diabetes

SMBG vs HbA1cSMBG vs HbA1c

Both are complimentary in Both are complimentary in managementmanagement

SMBG – predominantly point of care SMBG – predominantly point of care testing and type 1 and type 2 on testing and type 1 and type 2 on insulin treatment.insulin treatment.

UtilityUtility

A1c serves as check on accuracy of A1c serves as check on accuracy of meter.meter.

Adequacy of SMBG testing Adequacy of SMBG testing schedules.schedules.