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HbA1c testing for type 2 diabetes in general practice

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Almost one million Australian adults live with from type 2 diabetes (in addition, there are perhaps another 500,000 undiagnosed patients), making diagnosis and management a large and growing problem. 
 
In fact, in diabetes contributed to 16,700 deaths (10.5% of all deaths) in Australia in 2018. Lifetime risk of developing the condition is at least one in three, and it is now the fourth most common condition managed in Australian general practice.
  
Diagnosis
Patients should be screened for risk of diabetes every three years from 40 years of age using the Australian type 2 diabetes risk assessment tool (AUSDRISK). People with an elevated AUSDRISK score (or some other risk factors) should be screened with fasting blood glucose (FBG) or HbA1c every three years.
 
HbA1c determinations are an aid in diagnosis of diabetes and identifying patients who may be at risk for developing diabetes, and are useful for the monitoring of long‑term blood glucose control in people with diabetes.
 
HbA1c is one of the glycated haemoglobins, a sub-fraction formed by the attachment of various sugars to the haemoglobin A molecule. As a result, HbA1c reflects the average blood glucose level during the preceding 2–3 months, rather than daily variations in blood glucose levels that may be seen in FBG test results.
 
HbA1c test result interpretation for high-risk asymptomatic patients is relatively straightforward.

Test result	Interpretation	Suggested action
<6% (42 mmol/mol)	Diabetes unlikely	Retest in three years
6–6.4% (42–46 mmol/mol)	High risk/diabetes possible	Retest in one year
≥6.5% (48 mmol/mol)	Diabetes likely	Retest for asymptomatic patients

 
Of course, as with all diagnostic tests, HbA1c test result interpretation should be used in conjunction with information from other diagnostic procedures and clinical evaluations.

In particular, diagnosis in an asymptomatic person should not be made on the basis of a single abnormal plasma glucose or HbA1c value alone. It is also important to note that there are some conditions that can mean HbA1c may lack accuracy and in which fasting blood glucose or oral glucose tolerance test (OGTT) may assist diagnosis.
 
Abnormally low HbA1c can be caused by:

• anaemia
• recovery from acute blood loss
• blood/iron transfusions
• chronic blod loss
• chronic renal failure (variable). 

Abnormally high HbA1c can be caused by:

• iron deficiency anaemia
• splenectomy
• alchoholism. 

In addition, HbA1c is an unreliable measure of glycaemic management in the first four weeks of pregnancy.
 
HbA1c tests can be run in the lab, or on point-of-care testing (POCT) devices. POCT offers lab-like performance with strong correlation to lab instruments, fast turnaround time for results (around six minutes), and can facilitate clinical and administrative workflows in general practices clinics. 
 
POCT devices also need a very small sample size – 1–2 drops (2 μl) – of capillary or venous whole blood, and often utilise a disposable finger prick lance for sample collection.
 
While lab tests are convenient and economical (especially when ordered with other tests), there are some additional advantages to POCT. The American Diabetes Association asserts that POCT may offer the ability for more timely treatment changes.

And while the POCTs are typically more expensive, there may be savings in the reduced need for follow-up visits, which may make POCT more cost effective.
 
Monitoring
HbA1c has been the gold standard for monitoring long-term glycaemic management since 1976. Monitoring is usually recommended at three-month intervals; however, a six-month interval may be appropriate with stable diabetes.
 
The general HbA1c target in people with type 2 diabetes is ≤7% (≤53 mmol/mol), though there may be instances where 6.5% is a more appropriate target for a patient, or a less stringent target may also be appropriate. A threshold of 6.5% (48 mmol/mol) is linked to escalating microvascular disease.
 
We have seen that HbA1c testing is the benchmark for the diagnosis and monitoring of glycemic control, and POCT is a practical solution that allows GPs to take control of type 2 diabetes diagnosis and management.

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diabetes HbA1c point-of-care testing

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