Glycohemoglobin (GHb), Total

CPT Test code: 83036

Related Information:	Hemoglobin (Hb) A_1c
Specimen:	Whole blood
Volume:	7 mL
Minimum Volume:	0.5 mL (Pediatric EDTA whole blood tubes may be submitted. Please place the entire tube inside a transfer tube for shipment to the laboratory.)
Container:	Lavender-top (EDTA whole blood) tube is the preferred anticoagulant. Heparin and fluoride are also acceptable.
Collection:	Send entire tube to the laboratory. To avoid delays in turnaround time, please submit a separate lavender-top tube for each test requiring a lavender-top.
Storage Instructions:	Room temperature
Reference Interval:	• Diabetic adult: <9.0% • Healthy adult: 3.9% to 7.3% (DCCT/NGSP) Current ADA guidelines recommend a treatment goal <7.0% Hb A_1c for diabetic patients, which corresponds to a <9.0% glycohemoglobin result with this method.
Use:	This is an irreversible glucose-protein bond which extends through the life of an erythrocyte. Glycated hemoglobin values are used to assess long-term glucose control in diabetes, especially in insulin-dependent diabetics whose glucose levels are labile, and in whom blood and urine glucose measurements exhibit significant daily variation. GHb measurements reflect the level of control present during the preceding 100 to 120 days; more recent levels have greater weight. GHb is especially helpful when renal thresholds are high or low. Glycosylated hemoglobin measurements are less frequently needed in stable diabetics. In such patients, whose fasting glucose concentrations are fairly consistent from day to day, there is a correlation between glycosylated hemoglobin and single fasting glucose levels. Continued high levels of blood glucose are reflected in high GHb concentrations. Singer, et al suggest a diagnostic approach in which glycated hemoglobin may be substituted for the glucose tolerance test. They advocate it as well as an adjunct in gestational diabetes.¹ It is also useful in evaluation of fetal risk in known type II diabetics who become pregnant. Glycosylated hemoglobin predicts the progression of retinopathy.²
Limitations:	GHb measurements supplement conventional urine and blood glucose levels. Chronic blood loss, hemolytic anemia, or other setting for decrease in RBC lifespan, results in a decrease in the glycated hemoglobin level. Pregnancy may lower glycated hemoglobin. Chronic renal failure with or without dialysis leads to decreased levels of glycated hemoglobin.
Additional Information:	A useful test to reassure the patient who is well controlled, and to assess the status of insufficiently controlled patients. Measurement of glycated hemoglobin by affinity chromatography permits better differentiation of the degree of blood glucose control among diabetics than does hemoglobin A_1c or hemoglobin A₁ measurements.³
Footnotes:	1. Singer DE, Coley CM, Samet JH, et al, “Tests of Glycemia in Diabetes Mellitus − Their Use in Establishing Diagnosis and Treatment,” Ann Intern Med, 1989, 110(2):125-37. PubMed 2642375 2. Klein R, Klein BE, Moss SE, et al, “Glycosylated Hemoglobin Predicts the Incidence and Progression of Diabetic Retinopathy,” JAMA, 1988, 260(19):2864-71. PubMed 3184351 3. Teupe B, “Quantitative Determination of Glycated Hemoglobin Using Affinity Chromatography,” Symposium Proceedings: The Role of Glycated Hemoglobin in the Management of Diabetes, Akron, OH: Isolab, Inc, 1988, 9-16.