Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (978 page)

   HbH is composed of a tetramer of normal β chains, resulting in a markedly reduced production of α chains. HbH has mobility much faster at alkaline pH than HbA. (HbH disease is a severe form of α-thalassemia with only one α chain.)

HEMOGLOBIN A
_1C

   Definition

   Glucose combines with Hb continuously and nearly irreversibly during the life span of RBC (120 days). Therefore, glycosylated Hb (GHb) will be proportional to mean plasma glucose level during previous 6–12 weeks. May be reported as HbA
_1c
or as total of A
_1b
, A
_1a
, or A
_1c
.

Values may not be comparable with different methodologies and even different laboratories using same methodology.

   
Normal range
(ADA 2010 recommendations):

   <5.6%

   5.7–6.4% increased risk for diabetes

   >6.5% diabetic range

   The interpretation of HbA
_1c
levels is not intuitively obvious to many patients with DM, who are accustomed to thinking in terms of blood glucose levels. The American Diabetes Association (ADA) has called for laboratories to express HbA
_1c
results as estimated average blood glucose (eAG). ADA believes that eAG will be easier for patients to understand and will lead to improved management of DM.

   The formula recommended to calculate eAG is

eAG (mg / dL) = 28.7 × hemoglobin A1c − 46.7

   Use

   Monitoring compliance and long-term blood glucose level control in patients with diabetes.

   Index of diabetic control (direct relationship between poor control and development of complications).

   Predicting development and progression of diabetic microvascular complications.