Lab Index

Serum Glycosylated Hemoglobin Measurement Lab

Background

1. Measures amount of Glycosylated Hemoglobin (HbA1c) in blood
   • Provides accurate long-term index of average blood glucose level
   • Also called "glycated hemoglobin"
2. Physiology
   • Origin: glycosylated hemoglobin is blood glucose bound to hemoglobin
   • Function: amount of HbA1c depends on amount of glucose available in bloodstream over RBC 120 days lifespan
   • Excretion: via urine

Normal Reference Ranges

1. Adult:
   1. Nondiabetic: 4-5.9% of total Hb
   2. Pre-Diabetes: 5.9-6.4%
   3. Diabetes: > 6.4%
   4. Recommended target A1c for diabetics: < 7% [< 53 mmol/mol]
      • < 6.5% if can be achieved without significant hypoglycemia, short duration diabetes, type 2 DM treated with lifestyle changes, no significant cardiovascular disease
      • < 8% if extensive co-morbidities, limited life expectancy, difficult DM course management
2. Pediatric HbA1c
   • 4-5.9% of total Hb
     • Guideline A1c target: < 7.5% [< 58 mmol/mol]
     • Glycemic goals should be individualized and based on benefit-risk assessment

Interpretation

1. High (> 15% of total Hb)
   • Medical causes
     • Diabetes mellitus
     • Glycosuria
     • Hyperglycemia
     • Polycystic ovary syndrome
2. Low
   • Medical causes
     • Anemia (hemolytic, pernicious, sickle cell)
     • Renal failure (chronic)
     • Thalassemias
   • Factitious/spurious
     • Chronic blood loss
     • Effects of splenectomy
   • Drug causes: monoclonal antibodies

Related Tests and Testing Strategies

• Glucose, serum
• Glucose, urine

Technical Information

1. Collection of specimen
   • Draw 5 mL venous blood
   • Use lavender-top, pink-top, or green-top tube
   • Transport whole blood
2. Methods/Accuracy
   • HPLC/boronate affinity
   • Roche Tina-quant (spectrophotometry + turbidimetry)

References

1. American Diabetes A. Standards of Medical Care in Diabetes-2018. Diabetes Care. Jan 2018;41(Suppl 1):S1-S159
2. In: van Leeuwen AM, Bladh ML; (eds). Davis's Comprehensive Handbook of Laboratory and Diagnostic Tests with Nursing Implications, 7th ed., Philadelphia, PA: FA Davis Co., 2017
3. In: Pagana KD, Pagana T; (eds). Mosby's Manual of Diagnostic and Laboratory Tests, 6th ed., Elsevier, 2018