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PTD - 244

Test Directory -  HbA1c

Synonyms

Glycosylated Haemoglobin. Glycated Haemoglobin

Clinical Indications

HbA1c is used for the monitoring of glycaemic control in known diabetics. During the life of the red cells (normally 120 days) haemoglobin undergoes a degree of non-enzymatic glycation; HbA1c levels therefore reflect glucose levels during this period.

HbA1c may also be used for the diagnosis of Diabetes Mellitus

Request Form 

Combined Pathology Blood form (Yellow/Black or Blue for GP's)

Availability

On request

Specific Criteria

1. Monitoring glycaemic control in known diabetics.
2. Screening test for Diabetes Mellitus

Samples referred to Basildon Hospital for HbA1c analysis from other Hospitals should be packaged in accordance with our transportation policy and will be assumed to have met the specific criteria of the referring laboratory.

Patient Preparation

None required

Turnaround Time

3 days

Specimen

Whole blood

Volume

3 ml

Container

Purple top (EDTA) tube

Causes for Rejection

Unlabelled sample

Reference Range

Glycaemic Control

     (IFCC) Units mmol/mol

Excellent *

Less than 42

* check not having unrecognised hypoglycaemia

Excellent

43 to 47

Good

48 to 58

Less than Ideal

59 to 64

Poor

65 to 70

Very Poor

Greater than 70

A wall chart HbA1c conversion table is available (please click here)

For Diagnosis

A level of 48 mmol/mol or above is consistent with a diagnosis of Diabetes Mellitus. The diagnosis of diabetes in an asymptomatic person should not be made on the basis of a single abnormal plasma glucose or HbA1c value. At least one additional HbA1c or fasting plasma glucose test result with a value in the diabetic range is required.

Levels below 48 mmol/mol do not exclude Diabetes Mellitus.

Please click here to view 2011 WHO guidelines.

Limitations

Please note from April 2016 new methodology for HbA1c (HPLC). This assay provides accurate analytical results in the presence of most common haemoglobin variants.
Conditions like iron deficiency anaemia may increase red cell survival and yield falsely high results.
HbA1c is not a valid test for glycaemic control in patients with conditions which cause reduced red cell survival (e.g. haemolytic anaemias). An alternative test fructosamine should be used.
In homozygous forms of haemoglobin variants (e.g. HbSS), there is no HbA present and therefore no HbA1c; fructosamine should be requested in these circumstances.
This test should not be used for diagnosis of Diabetes Mellitus in the presence of Hb variants.
In the presence of Hb variants, long term glycaemic control should be assessed by comparison with previous results as reference ranges may not apply

Lab. Handling

Processing: Test code: GHB. Store whole blood at 4C in racks 79-81 in the cold room (CB23) prior to analysis.


Version 1.2 / November 2016                                                                                                  Approved by: Consultant Biochemist