Haemoglobin A1c

Alternative names, keywords

HbA_1c, glycated haemoglobin, HbA1c

Samples required

EDTA blood (purple cap/ yellow cap ring, 4 mL tube).

A separate EDTA sample is required for HbA_1c as other EDTA-requiring tests (e.g. PTH, FBC) have different processing requirements.

2 mL EDTA tubes (purple cap/ white cap ring) are available for paediatric samples however please note the 1.3 mL neonatal tubes cannot be processed.

Test indications

Test information

The assay detects all haemoglobin variants which are glycated at the β‑chain N‑terminus and which have antibody-recognizable regions identical to that of HbA_1c.

It can therefore be used for patients with the most frequent haemoglobinopathies (HbAS, HbAC,HbAE, HbAD), however please note caveats below.

Factors affecting test performance/ results

HbA_1c may be unreliable in the presence of Hb variants or when red cell turnover is altered. In either of these cases, HbA_1c must not be used for the diagnosis of diabetes mellitus.

Abnormal haemoglobins 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 glycaemic control that would be expected in patients with normal haemoglobin. Whenever it is suspected that the presence of an Hb variant (e.g. HbSS, HbCC or HbSC) affects the correlation between the HbA_1c value and glycaemic control, HbA_1c must not be used for the diagnosis of diabetes mellitus.

Any cause of shortened erythrocyte survival or decrease in mean erythrocyte age (e.g. haemolytic disease, homozygous sickle cell trait, pregnancy, recent significant or chronic blood loss) will reduce exposure of erythrocytes to glucose with a consequent decrease in mmol/mol HbA_1c values. HbA_1c must not be used for diagnosis of DM in these situations.

Glycated HbF is not detected by the HbA_1c assay but HbF contributes to the the total Hb used to calculate mmol/mol HbA_1c. Specimens containing high amounts of HbF (> 10 %) may therefore result in lower than expected mmol/mol HbA_1c values.

There is no significant interference from glucose up to a concentration of 55.5 mmol/L.

Results should always be assessed in conjunction with the patient’s medical history, clinical examination and other findings.

Reference range

Diabetes monitoring

Individualised targets recommended - see NICE NG 28.

Diagnosis

_{Source: NHS Diabetes Prevention Programme}, _{NICE PH38 ’Type 2 diabetes: prevention in people at high risk’.}

Turnaround time

24 hours. Samples arriving on Friday afternoon, at the weekend, or on Bank Holidays will be analysed on the next routine working day.

Enquiries

Biochemistry (Automation)