- RBCs have a life cycle of 8-12 weeks.
- HbA1C is formed by glycation (attachment of glucose) to Hb and reflects glucose concentration of the previous 2-3 months.
- HbA1C diagnostic of DM – 6.5% (48mmol/mol)
- goal of DM management – <7%
Factors that alter the HbA1C value:
- erythrocyte life span
- increased lifespan – increases time RBC is exposed to glucose, increases HbA1C falsely, (ex. splenectomy)
- decreased lifespan – HbA1C decreased (ex. hemolytic anemia)
- decreased erythropoiesis – increases mean age of RBC, increases HbA1C level (ex. iron deficiency anemia)
- severe CKD decreases erythropoietin levels
- severe hypertriglyceridemia and chronic alcoholism
- interferes with assay
- Hb variants – yields inaccurate results
- genetic factors or the “glycation gap”
- genes that affect RBC life span or glycation
ALTERNATIVE TESTING METHODS
- glycated albumin and fructosamine (measures all glycated serum protein)
- half life of albumin is 14-21 days; all glycated serum protein tests reflect average blood glucose concentrations over the previous 2-3 weeks
- not affected by RBC disorders but by serum protein abnormalities (i.e. nephrotic syndrome)
- daily fingerstick
- continuous glucose monitor
- serum 1,5 anhydroglucitol (1,5-AG) test
CONVERSION A1C EST AVE BLOOD GLUCOSE:
The formula for converting A1C to an estimated average blood glucose level, according to the American Diabetes Association, is (28.7 x A1C) – 46.7 = estimated average glucose.
O’Keeffe, Derek T., Spyridoula Maraka, and Robert A. Rizza. “Hba 1C In The Evaluation Of Diabetes Mellitus”. JAMA 315.6 (2016): 605. Web. 13 Feb. 2016.
Nhrmc.org,. N.p., 2016. Web. 13 Feb. 2016. https://www.nhrmc.org/~/media/files/ diabetes-health-plan/class-materials/diabetes-overview-class/conversion-table-revised-12-30-14.pdf?la=en