Specimen Collection

Only whole blood can be used. EDTA tubes that have been centrifuged and plasma removed are not suitable for HbA1c analysis.

Specimen Stability

Room temperature	up to 72 hours
Refrigerated	up to 7 days
Frozen	up to 3 months at -80 o C if frozen within 8 hours of collection

4 mL EDTA Blood (Always Required)

0.5 mL Paediatric Micro-EDTA Blood (Always Required)
Reference Intervals

When performed for diagnosis or cardiovascular disease risk screening:

mmol/mol (IFCC units)
40 or less	Virtually excludes diabetes. No need to repeat until next scheduled CVD risk assessment
41 - 49	Suggests abnormal glucose tolerance. Recommend diet/lifestyle changes and assess/manage all CVD risk factors. Repeat annually unless symptomatic in interim.
50 or greater	Supports a diagnosis of diabetes but confirmation is required in asymptomatic patients.

Glucose-based diagnostic criteria should always be used in cases of haemoglobinopathy or increased red cell turnover.

In those with confirmed diabetes

mmol/mol (IFCC units)
less than 50	Excellent control; increased risk of hypoglycaemia if on insulin/sulphonylureas
50 - 54	Very good control; some risk of hypoglycaemia if on insulin/sulphonylureas
55 - 64	May be appropriate and acceptable in many individuals but higher than ideal. Microvascular complication risk increases markedly above 55 mmol/mol
65 - 79	Suboptimal glycaemic control. Consider more intensive treatment. Microvascular complication risk increases markedly above 55 mmol/mol
80 - 99	Poor glycaemic control. More intensive treatment recommended. Microvascular complication risk increases markedly above 55 mmol/mol
100 or more	Very poor glycaemic control. Warrants immediate action

In pregnancy

mmol/mol (IFCC units)
<41	Unlikely to have pre-existing glucose tolerance/diabetes, but can develop gestational diabetes. Follow local guidelines.
41 - 49	May reflect glucose intolerance. Follow local guidelines, or offer 75g oGTT at 24-28 weeks.
50 or greater	Levels consistent with pre-existing diabetes. Refer to local diabetes in pregnancy service.

Glycated haemoglobin measurements may be misleading in cases of haemoglobinopathy or increased red cell turnover.

Uncertainty of Measurement: 6%

Units conversion:

NGSP units (%) = 0.09148 x IFCC units + 2.15

IFCC units (mmol/mol) = 10.93 x [NGSP units - 2.15]

%	mmol/mol
4.0	20
4.5	26
5.0	31
5.5	37
6.0	42
6.5	48
7.0	53
7.5	58
8.0	64
8.5	69
9.0	75
9.5	80
10.0	86
10.5	91
11.0	97
11.5	102
12.0	108
12.5	113
13.0	119

Turnaround Time: Within 2 days

Only available 0800 - 1500 weekdays only

Assay Method

Principle: Capillary electrophoresis

Assay: Sebia

Analyser: Capillaries 3

Diagnostic Use and Interpretation

Haemoglobin A1c is an index of metabolic control in patients with diabetes mellitus.

The result correlates best with the mean level of blood glucose during the previous 8 weeks, with the mean blood glucose during the last 30 days prior to testing contributing about 50% of the final result.

HbA1c is formed continuously during the lifespan of the RBC. The HbA1c level depends on (a) the average glucose level , (b) the mean RBC age, and (c) other factors which are not well understood but which are constant for an individuial.

Unexpectedly low HbA1c occurs when there is increased RBC turnover (reduced mean RBC age):

- Ongoing blood loss, with replacement, e.g. GI bleeding, menorrhagia, venesection

- Haemolysis

- Unstable haemoglobin (e.g. some haemoglobinopathies, thalassaemias)

- Renal failure (red cell lifespan shortened up to 40%)

- Starting iron, B12 or folate in deficient patientsor starting erythropoietin in renal failure patients

- Recent transfusion

- Pregnancy

- HIV-infected patients on antiretrovirals

Unexpectedly high HbA1c occurs when there is increased mean red cell age:

- Nutritional iron deficiency

- Hyposplenism

- Bone marrow failure

These influences mean that interpretation of the HbA1c level should always be in the context of other clinical and laboratory data.

Analytical Issues

Some variant haemoglobins produce erroneous HbA1c results which are often method specific. The possibility of an analytical artefact should be considered when:

- Widely varying results between different laboratories (which may be using different methods)

- Extreme HbA1c results (e.g. over 150 mmol/mol, or below 20 mmol/mol)

- Lack of apparent correlation between HbA1c and repeated glucose results

- Known haemoglobinopathy or presence of significant amounts of HbF.

Contact Information

Emails to chemicalpathologist@adhb.govt.nz will receive priority attention from the on-call chemical pathologist.

If the query concerns a specific patient please include the NHI number in your email.

If email is not a suitable option, please contact the on-call chemical pathologist via Lablink (Auckland City Hospital ext. 22000 or 09-3078995).

Individual chemical pathologists may be contacted but will not be available at all times.

After-hours : contact Lablink (Auckland City Hospital ext. 22000 or 09-3078995) or hospital operator for on duty staff after hours.

Dr Samarina Musaad (Clinical Lead) : SamarinaM@adhb.govt.nz ext. 22402

Dr Cam Kyle: CampbellK@adhb.govt.nz ext 22052

Dr Weldon Chiu: WeldonC@adhb.govt.nz ext. 23427

Dr Campbell Heron: CHeron@adhb.govt.nz ext. 23427

Dr Sakunthala Jayasinghe: Sakunthala@adhb.govt.nz ext. 23427

Last updated at 15:26:00 06/01/2025