• Credits
  • Section Writer: Dr. Om J Lakhani
  • Section Editor: Dr. Om J Lakhani

Support us:

1. Support us by purchasing our book - Click here for more details: Volume 1- THE BEST OF NOTES IN ENDOCRINOLOGY BOOK SERIES
2. Support you by Becoming a YouTube member (Click here)

• Q. Who was the first to describe HbA1c?
  • Rhabar et al
• Q. What is the most appropriate Term for HbA1c?
  • It is glycated hemoglobin and not glycosylated hemoglobin
  • Glycosylated suggests it is an enzymatic process whereas, in reality, it is a non-enzymatic reaction
• Q. What does 1c stand for in HbA1c ?
  • 1c stands for the order of hemoglobin molecules on electrophoresis
• Q. On what chain of the hemoglobin is the glucose added?
  • It is added to the beta-chain of the hemoglobin
• Describe the steps to HBA1c formation?
  • Glucose binds to the N terminal of valine residue on the Beta chain of HbA
  • Formation of Schiff’s bases (Aldimine) non-enzymatically →
  • Converts to Amadori product (Irreversible ketamine) →
  • Intermediate glycosylation production →
  • Cross-links- Advanced glycosylation end products
• Q. What part of the above reaction are we measuring when we measure HbA1c?
  • We are measuring the irreversible ketoamine and not the Schiff’s base aldimine
  • The Aldimine is transient and reflects acute glucose fluctuation
  • While the Ketoamine is irreversible and represents chronic hyperglycemia
• Q. HbA1c reflects what period of glycemic control?
  • It reflects truly the glycemic control of only the last 8 weeks
  • Even though the idea is that it lasts the entire period of RBC which is 120 days in reality it only lasts for 8 weeks
  • 50% of the HbA1c is formed in the last 1 month and that of last 3-4 months only contribute 10%
• Q. What are more glycated – The older RBCs or reticulocytes?
  • The older RBCs are more glycated than reticulocytes
• Hba1c assays and methods
• Q. Describe the various methods for HbA1c estimation.
  • 
• Q. Which assay was used in the DCCT trial?
  • It used D10 cation exchange HPLC
  • To be specific- BIORAD DIAMAT using Bio-Rex 70 resin was used in DCCT and also UKPDS
• Q. What is ADAG?
  • It is the study that came up with the estimated average glucose (eAG) formula for HbA1c
  • Study was called "A1c Derived glucose"
• Q. What is the ADAG formula?
  • eAG = 28.7 x HbA1c – 46.7
• **Standardization **
• Q. What is the difference between standardization and harmonization?
  • Harmonization- calibrating the assay using an arbitrarily chosen standard
  • Standardization- calibrating the assay using a standard that is of high order
• Q. What is the current standardization process for HbA1c?
  • Old standardization was done by NGSP (National glycohemoglobin standardization program) which standardized using an assay that was used in DCCT
  • This assay was an HPLC ion exchange electrophoresis
  • It reported as % of total hemoglobin
  • It was harmonization and not standardization
  • The newer standardization is given by IFCC (international federation for clinical chemists)
  • It is a different assay
  • It reports the value as mmol/mol
• Q. How is the IFCC reference derived?
  • 3 steps
    • Step 1
      • Hb separated from lysed RBC is cleaved using endoproteinase
    • Step 2
      • The glycated and non-glycated particles are separated using HPLC
    • Step 3
    • The glycated particles which are separated are measured using capillary electrophoresis
• Q. How is the current reporting done?
  • According to the current consensus the reporting is to be done in three formats
  • IFCC – using mmol/mol value
  • NGSP - % value
  • eAG from ADAG formula
• Q. What is the relation between the new assay of IFCC and DCCT assay?
  • The new assay gives a value that is 1.5% lower than the older assay
• Q. How is the NGSP value of % divided by the IFCC value?
  • Using the formula  0.0914 * IFCC + 2.152
• Q. Using the formula what is HbA1c <7 % in IFCC terms?
  • It is around 53 mmol/mol
• Q. Which anticoagulant is used while taking an HbA1c blood sample?
  • EDTA
• Q. What should the CV be for HbA1c?
  • Interlaboratory  -  CV <3%
  • Intralaboratory  -CV  <5%
• FALSE VALUES
• Q. What are the common causes of false high and false low values of HbA1c?
  • False High
    • Iron deficiency anemia
    • B12 and folic acid deficiency
    • CKD (uremia)- carbamylated hemoglobin
    • Asprin
    • HbF and HbG
  • False low
    • HbS and HbC
    • Hemolytic anemia
    • Pregnancy
• Q. Do the Hemoglobin variants always create a problem?
  • No
  • The newer HPLC and Capillary electrophoresis methods tend to separate the Hb variants and hence do not interfere with the test results
  • The chemical methods do not normally separate the Hb variants
• Q. What happens in CKD?
  • Carbamylated Hb- false high
  • Increase hemolysis and use of EPO  - false low
• Q. What are the racial differences in HbA1c?
  • They are uncertain
  • But Africans and Hispanics- Higher HbA1c
  • Asian and Caucasians- lower HbA1c
• Q. What is the relation between HBA1c and age?
  • With every decade of life HBA1c increase by 0.1% or 1 mmol/mol
• Q. Why does HbA1c correlate so well with Diabetic microvascular complications
  • Glucose enters the RBC via the GLUT1 channel
  • here is bonds to the N-terminus of the Hemoglobin beta-chain to produce an HbA1c
  • Glucose also enters the tissue in which microvascular complications are seen via GLUT1
  • hence the glucose levels intracellular in these organs (kidney, retina, neurons) are similar to that in RBC
  • hence HbA1c correlates well with microvascular complications
• Q. What is the Glycation gap?
  • glycation gap is the difference between the measured HbA1c and the predicted HbA1c
  • this article writes that in almost 30% of patients with Type 1 Diabetes - the HbA1c values do not correlate with the measured SMBG values!
• Q. Does the type of sample- arterial, venous, or capillary affect the results?
  • No data regarding arterial, but generally capillary testing is similar to venous
  • the difference is NOT significant
• Q. Does Point of care testing for HBA1c give inferior results?
  • Not necessarily
• Q. Does HbA1c show diurnal variation ?
  • No
• Q. What about seasonal variation?
  • Yes
  • Levels may be elevated in Winter #ClinicalPearl
• Q. How long can it be stored?
  • In normal conditions, it can be stored easily
  • Storage at 4 degrees is preferred for ion-exchange methods
  • Long-term storage upto 10 years at -70 degrees is possible
• Q. Does drug intake interfere with the value?
  • Vitamin C and Aspirin in very high doses may have an impact
  • but are megadoses and not clinically relevant
• ^^#ClinicalPearl- 50% of the value of HbA1c is impacted by the glucose value in the recent months time^^ - so it is skewed mean and not exact mean of 3 months
• Q. Does Iron deficiency anemia impact the HbA1c? #ClinicalPearl
  • Yes
  • it increases the HbA1c because of increased RBC lifespan
  • giving iron to these patients lowers the HbA1c
• Q. What happens to HbA1c in Sickle cell anemia?
  • HbA1c would not be accurate in Sickle-cell anemia
  • since SCA is associated with a defect in Beta-chain and HbA1c has to do with the beta-chain
  • Any form of Hemoglobinopathy that leads to lower or abnormal beta-chain leads to abnormality in HbA1c values
• Q. What HbA1c value can be useful for the diagnosis of Gestational Diabetes mellitus (GDM)? #ClinicalPearl #Googlekeep
  • Ball-park figure- HBA1c of >5.9% strongly correlates with GDM
• Q. Does hypothyroidism have any relation with HbA1c? #ClinicalPearl
  • Some studies have shown that Subclinical hypothyroidism and Overt hypothyroidism are associated with a mild increase of HbA1c which corrects on Levothyroxine supplementation
• Q. Is HbA1c reliable in a patient with cirrhosis? #ClinicalPearl
  • No
  • because of several factors HbA1c is not very reliable in patients with CLD
• Q. What about CKD? #ClinicalPearl
  • Some experts say
    • Don't use HBA1c for diagnosis of diabetes in CKD 1-3 - can use for monitoring therapy
    • Don't use HBA1c for diagnosis or treatment in patients with CKD 4/5 or ESRD
• Q. Which other drugs or factors can impact HbA1c?
  • Dapsone significantly reduced HbA1c and hence HbA1c should not be used in patients receiving Dapsone
  • Vitamin E may also reduce HBA1c levels
  • Hydroxyurea may cause aberrant HbA1c levels
• Q. Why does Dapsone reduce the HbA1c?
  • By causing hemolysis
  • several antiretroviral drugs like Ribavarin also impact HbA1c in a similar way
• Q. Summarize the conditions producing false high and false low HBA1c.
  • 
• Q. In which condition should you consider hemoglobinopathy and the aberrant result of HbA1c?
  • 1. HBA1c >15%
  • 2. HBA1c and SMBG do not correlate
  • 3. A dramatic difference in HBA1c based on change of lab or methodology
• Q. What is the impact of Hypertriglyceridemia on HbA1c?
  • it produces false elevation of HbA1c
  • Similar thing is seen with glucocorticoids use