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Laboratory:

Clinical Biochemistry

Test Name:

HEMOGLOBIN A1C - (B)

Test Code: GYHB

Clinical Information:

Test Indications: Hemoglobin A1c (HbA1c) testing is used for monitoring long term glycemic control in diabetic patients. The HbA1c level reflects the average blood glucose level during the preceeding 2 to 3 months. The risk of diabetes complications such as diabetic nephropathy and retinopathy increases with poor metabolic control. HbA1c measurement is therefore a useful indicator for the prediction of diabetes complications.
The Canadian Diabetes Association (CDA), American Diabetes Association (ADA), International Expert Committee (IEC) and the World Health Organization (WHO) recommend the use of HbA1c to diagnose diabetes, using a threshold of 6.5%. The HbA1c assay used by our laboratory is a validated assay standardized to the National Glycohemoglobin Standardization Program ((NGSP) - Diabetes Complications Trial (DCCT) reference and meets the diagnostic criterion for diabetes diagnosis.
Recommendations: See: Definition, Classification and Diagnosis of Diabetes, Prediabetes and Metabolic Syndrome. Diabetes Canada Clinical Practice Guidelines Expert Committee. Can J Diabetes 42 (2018) S10-S15

Collection Devices:

Preferred Device:	1 - EDTA 4 mL NO GEL Tube(s) - Full Tube Collection EDTA 4 mL NO GEL Tube(s) - Full Tube Collection Manufacturer: Becton Dickinson & Company Catalogue #: 367861
Alternate Device:	2 - Microtainer(s) - EDTA, NO GEL (0.5 mL) to fill line Microtainer(s) - EDTA, NO GEL (0.5 mL) to fill line Manufacturer: Becton Dickinson & Company Catalogue #: 363706

Both microtainers should contain at least 0.5 mL blood in each.

Specimen Required:

Stability 7 days refrigerated, 6 months frozen

Referral:

Ship whole blood specimen in primary EDTA tube. Store and ship refrigerated.

Requisition:

_SH Biochemistry Hematology Requisition (R250-10-92)

_SH Hospital Biochemistry Hematology Non Winnipeg Brandon (R250-10-91)

_SH Winnipeg Brandon Biochemistry Hematology Requisition (R250-10-94)

_SH Winnipeg Brandon Hospital Biochemistry Hematology Requisition (R250-10-93)

Reference Values:

4.0 - 6.0 %

Please consult the Canadian Diabetes Association Clinical Practice Guidelines at http://guidelines.diabetes.ca/ for the interpretation of HbA1c in various clinical conditions.

Limitations of HbA1C as a diagnostic marker:

1) For diagnostic purposes, % HbA1c values (DCCT/NGSP) should be used in conjunction with information from other diagnostic procedures and clinical evaluations.

2) Care must be taken when interpreting any HbA1c result from patients with Hb variants. Abnormal hemoglobins might affect the half-life of the red cells or the in vivo glycation rates. In these cases even analytically correct results do not reflect the same level of glycemic control that would be expected in patients with normal hemoglobin.28 Whenever it is suspected that the presence of an Hb variant (e.g. HbSS, HbCC or HbSC) affects the correlation between the HbA1c value and glycemic control, HbA1c must not be used for the diagnosis of diabetes mellitus.

3) Any cause of shortened erythrocyte survival or decrease in mean erythrocyte age will reduce exposure of erythrocytes to glucose with consequent decrease in mmol/mol HbA1c values. Causes of shortened erythrocyte lifetime might be hemolytic anemia or other hemolytic diseases, homozygous sickle cell trait, pregnancy, recent significant or chronic blood loss, etc. Similarly, recent blood transfusions can alter the % HbA1c values. Caution should be used when interpreting the HbA1c results from patients with these conditions. HbA1c must not be used for the diagnosis of diabetes mellitus in the presence of such conditions.

4) Glycated HbF is not detected by the assay as it does not contain the glycated β-chain that characterizes HbA1c. However, HbF is measured in the total Hb assay, and as a consequence, specimens containing high amounts of HbF (> 7 %) may result in lower than expected % HbA1c values.

5) HbA1c value is not suitable for the diagnosis of gestational diabetes.

6) In very rare cases of rapidly evolving type 1 diabetes, the increase of the HbA1c values might be delayed compared to the acute increase in glucose concentrations. In these conditions, diabetes mellitus must be diagnosed based on plasma glucose concentrations and/or the typical clinical symptoms.

Availability:

Weekdays