HbA1c for Diagnosis

Purpose:
HbA1c is used for both the diagnosis (Type 2) and monitoring of diabetes (Type 1 & 2) and as part of the NHS England Health Check for subjects that on initial screen are identified as having a risk of developing diabetes.

The diagnosis of diabetes is based on the measurement of plasma glucose or glycated haemoglobin (HbA1c), with a cut off value for HbA1c of 48 mmol/mol used as the diagnostic threshold for diabetes; however, plasma glucose remains the preferred test in people with symptoms who are suspected of having type 1. Diagnosis and management of type 2 diabetes (HEARTS-D). Geneva]: World Health Organization; 2020 (WHO/UCN/NCD/20.1).

HbA1c is commonly used to monitor glycaemic control in both Type 1 and Type 2 diabetes as it provides a measure of average plasma glucose over the preceding 8 – 12 weeks.

Diabetes (type 1 and type 2) in children and young people: diagnosis and management. NICE guideline [NG18]
Recommendations: HbA1c targets and monitoring

HbA1c should be measured using methods calibrated according to International Federation of Clinical Chemistry (IFCC) standardisation.
Children and young people with type 1 diabetes – HbA1c target level of 48 mmol/mol or lower will minimise risk of long-term complications.
Children and young people with type 1 diabetes who have an HbA1c level above 48 mmol/mol that any reduction in HbA1c level reduces their risk of long-term complications.
HbA1c should be measured 4 times a year in children and young people with type 1 diabetes.
Diabetes services should document the proportion of children and young people with type 1 diabetes who achieve an HbA1c level of 53 mmol/mol or lower.

Type 2 diabetes in adults: management. NICE guideline [NG28]
Recommendations: HbA1c measurement and targets

HbA1c levels in adults with type 2 diabetes should be measured every: 3 to 6 months (tailored to individual needs) until HbA1c is stable on unchanging therapy or 6 months once the HbA1c level and blood glucose lowering therapy are stable.
HbA1c should be measured using methods calibrated according to IFCC standardisation.
NICE has produced a patient decision aid on agreeing HbA1c targets, which also covers factors to weigh up when discussing HbA1c targets with patients.
For adults whose type 2 diabetes is managed either by lifestyle and diet, or lifestyle and diet combined with a single drug not associated with hypoglycaemia, aim for an HbA1c level of 48 mmol/mol. For adults on a drug associated with hypoglycaemia, aim for an HbA1c level of 53 mmol/mol.
In adults with type 2 diabetes, if HbA1c levels are not adequately controlled by a single drug and rise to 58 mmol/mol or higher: reinforce advice about diet, lifestyle and adherence to drug treatment and support the person to aim for an HbA1c level of 53 mmol/mol and intensify drug treatment.

Scope:
Weqas provides 3 different Programmes for HbA1c based on the clinical utility of the HbA1c test. This programme aims to cover the clinically relevant ranges, encompassing the diagnostic cut-off level, of 48mmol/mol Hb for the diagnosis of diabetes. However, the analytical measuring range will also be assessed where appropriate. The programme is suitable for Laboratories utilising their HbA1c test for the diagnosis of diabetes, however, this Programme should also be used if the Laboratory method in use is also used for monitoring HbA1c for the management of diabetes.

Fresh EDTA whole blood from individual diabetic patients and healthy volunteers are distributed monthly. These samples reflect the wide range of HbA1c seen in healthy individuals and in Diabetic patients. Challenging samples from patients with known Hb variants are also distributed to assess current practice.

The HbA1c reference target values in the Weqas programme are assigned using IFCC secondary reference methods in an IFCC network laboratory. The programme allows for the assessment of the organisation’s and method’s performance, including linearity, trueness, bias, and imprecision. The acceptable performance specification used in this programme reflects the clinical requirement for diagnosis of diabetes.

Key Features:

Whole blood samples are collected from healthy volunteers and patients with Type II Diabetes.
Samples cover non-diabetic, diagnostic cut-off level, (48mmol/mol Hb), pathological and analytical ranges.
Case studies including challenging samples with known Hb variants distributed.
Scoring based on clinically relevant hybrid Milan Model 1 and 2 performance specification.
Programme assesses both laboratory and method performance, including trueness, bias, within and between batch imprecision.
Trueness is assessed using the IFCC secondary reference methods.
Additional samples are distributed annually as part of the European HbA1c Trial to assess the performance across all countries and all manufacturers. The full report is provided as part of the programme.