A test tube with a HbA1c test label

We have changed the equipment we use for measuring HbA1c (average blood glucose levels). We are now using a TOSOH analyser, and our Biochemistry Team would like to share some information about the changes and scenarios that apply to various patient groups.

The clinical utility of HbA1c will remain for aiding in the diagnosis and monitoring of Diabetes Mellitus (DM) and non-diabetic hyperglycaemia. The cut-off values and interpretation of the numerical results also remain unchanged. Overall, the HbA1C results will be commutable between the methods for much of the population. In addition, the electronic requesting of the HbA1c test through ICE/EPR will continue unchanged.

The new equipment is expected to enhance diagnostic accuracy and improve monitoring.

There are some new limitations associated with reporting HbA1c. It’s possible that some individuals will be carriers of a benign variant of haemoglobin. There will also be rare cases of individuals with haemoglobinopathies (these will likely be known, e.g. Sickle cell disease). In both cases, we cannot report the HbA1c result accurately for aiding diagnosis of DM. Please note advice for these patient scenarios below.

Laboratory comments will be added to reports when a possible haemoglobin variant has been detected with information on how to monitor patients already diagnosed with DM and how to diagnose new patients with DM. We are unable to report the specific variant phenotype, however, in cases when a haemoglobinopathy is suspected, we will advise discussion with Clinical Haematology.

If you would like any further information, please contact our Consultant Biochemists,  chris.cockcroft2@cht.nhs.uk or daniel.herrera2@cht.nhs.uk.

Changes to HbA1c reporting – scenarios based on different patient groups

Scenario 1: Diagnosis of DM for haemoglobin heterozygous variant carriers

If the Individual has no clear history of HbA1c >47 mmol/L the HbA1c will be non-reportable. Then diagnosis and monitoring using plasma glucose is required (serum fructosamine cannot be used).

Scenario 2: Monitoring glycaemic control in DM for haemoglobin heterozygous variant carriers

If the Individual has had a least 2 previous HbA1c >47 mmol/L results that are consistent with DM or have been diagnosed based on plasma glucose (see scenario 1). Then for certain variants the HbA1c can be used for non-diagnostic monitoring purposes. The typical exception being individuals with HbE variants (see scenario 3).

Scenario 3: Un-reportable HbA1c due to haemoglobinopathies and HbE variants

If in rare cases the HbA1c is not reportable due to a haemoglobinopathy or the benign HbAE/EE phenotype. Then diagnosis using plasma glucose and laboratory monitoring using plasma glucose and serum fructosamine is now available. Note, fructosamine measures glycated proteins and reflects the average blood glucose concentration over the previous 2-3 weeks. This request is now available on ICE and EPR for requestors.

Scenario 4: Potentially unreportable HbA1c due to other pre-analytical factors

Please note, as with the outgoing methodology, the remaining limitations of interpreting HbA1c remain. These include conditions with high-red cell turnover, iron deficiency anemia, recent B12 infusion, blood transfusion. Please also note that HbA1c should not be used for diagnosis of type-1 DM, plasma glucose is always required.

Useful references: