Screening for type 2 diabetes

Screening for diabetes is the process of identifying people who are likely to have diabetes, and then using diagnostic testing to confirm whether these people do or do not have diabetes.

Screening for type 2 diabetes and pre-diabetes is justified because of the increasing number of people with these conditions. New Zealand guidelines recommend that screening for type 2 diabetes be undertaken in conjunction with cardiovascular risk assessment. (1)

Criteria for screening in men

Men should be screened for type 2 diabetes at 3 to 5 yearly intervals depending on risk.

From age 45 years

Men who do not have symptoms and do not have known cardiovascular risk factors.

From age 35 years

  • Maori, Pacific peoples or Indo-Asian peoples (Indian including Fijian Indian, Sri Lankan, Afghani, Bangladeshi, Nepalese, Pakistani, Tibetan)
  • In the presence of cardiovascular factors – family history risk factors:
    • Diabetes in first-degree relative (parent, brother or sister).
    • Premature coronary heart disease or ischaemic stroke in a first-degree relative (father or brother <55 years, mother or sister <65 years).
  • In the presence of cardiovascular factors – personal history risk factors:
    • People who smoke (or who have quit only in the last 12 months).
    • Prior blood pressure ≥160/95 mm Hg.
    • Prior TC:HDL ratio ≥7.
    • Known borderline HbA1c (41-49 mmol/mol) or fasting glucose 6.1-6.9 mmol/l).
    • BMI ≥30 kg/m2 or truncal obesity (waist circumference ≥94 cm in men).
    • Estimated glomerular filtration rate (eGFR) <60 ml/min/1.73m2.

From age 25 years

  • Individuals with ischaemic heart disease (angina or myocardial infarction), cerebrovascular disease, or peripheral vascular disease
  • Those on long-term steroid or antipsychotic treatment
  • Individuals who are obese (BMI ≥30; or BMI ≥27 kgm-2 for Indo-Asian peoples)
  • If there is a family history of early age of onset type 2 diabetes in more than one first-degree relative.

Criteria for screening in women

Women should be screened for type 2 diabetes at 3 to 5 yearly intervals depending on risk.

From age 55 years

If they don't' have any symptoms and do not have known cardiovascular risk factors.

From age 45 years 

  • Maori, Pacific peoples or Indo-Asian peoples (Indian including Fijian Indian, Sri Lankan, Afghani, Bangladeshi, Nepalese, Pakistani, Tibetan)
  • In the presence of cardiovascular factors – family history risk factors:
    • Diabetes in first-degree relative (parent, brother or sister).
    • Premature coronary heart disease or ischaemic stroke in a first-degree relative (father or brother <55 years, mother or sister <65 years).
  • In the presence of cardiovascular factors – personal history risk factors:
    • People who smoke (or who have quit only in the last 12 months).
    • Gestational diabetes.
    • Polycystic ovary syndrome.
    • Prior blood pressure ≥160/95 mm Hg.
    • Prior TC:HDL ratio ≥7.
    • Known borderline HbA1c (41-49 mmol/mol) or fasting glucose 6.1-6.9 mmol/l).
    • BMI ≥30 kg/m2 or truncal obesity (waist circumference ≥80 cm in women).
    • Estimated glomerular filtration rate (eGFR) <60 ml/min/1.73m2.

From age 25 years

  • Individuals with ischaemic heart disease (angina or myocardial infarction), cerebrovascular disease, or peripheral vascular disease
  • Persons on long-term steroid or antipsychotic treatment
  • Individuals who are obese (BMI ≥30; or BMI ≥27 kgm-2 for Indo-Asian peoples)
  • Have a family history of early age of onset type 2 diabetes in more than one first-degree relative.
  • Have a past personal history of gestational diabetes mellitus.

Criteria for screening in children and young adults

Obese children and young adults (BMI ≥30 kg/m2 or BMI ≥27 kg/m2 for Indo-Asian peoples) should undergo screening for type 2 diabetes if:

  • there is a family history of early-onset type 2 diabetes
  • they are of Mäori, Pacific or Indo-Asian* ethnicity.

Screening tests for diabetes

HbA1c is the recommended diagnostic screening test (1)

  • Point-of-care assays are not sufficiently accurate for use in diagnosis nor is there a permanent record of the result.
  • If it is not possible to measure HbA1c, or there are concerns about its validity, then a fasting plasma glucose is recommended (2). A fasting glucose might also be measured at the time of CVD risk assessment of lipids.
  • Oral glucose tolerance test (OGTT) should only be used when there is uncertainty about the validity of HbA1c measures in specific patients – for example in the presence of haemoglobinopathy or abnormal red cell turnover, or where there are special clinical reasons.

Interpreting the results

People with symptoms (symptomatic)

Result Action Why

HbA1c ≥ 50 mmol/mol
             and, if measured,
fasting glucose ≥ 7.0 mmol/L

OR

random blood glucose ≥ 11.1 mmol/L

No further tests required Diabetes is confirmed

People without symptoms (asymptomatic)

Result

Action

Why

HbA1c ≥ 50 mmol/mol and, if measured, fasting glucose ≥ 7.0 mmol/LOrrandom blood glucose ≥ 11.1 mmol/L

 Repeat HbA1c or a fasting plasma glucose

Two results above the diagnostic cutoffs, on separate occasions are required for the diagnosis of diabetes* 

HbA1c  41 to 49 mmol/mol and, if measured, fasting glucose 6,1-6.9 mmol/L

Advise on diet and lifestyle modification. Repeat the test after 6 to 12 months

 Results indicate 'pre-diabetes' or impaired fasting glucose*

HbA1c ≤ 40 mmol/mol  and, if measured, fasting glucose ≤ 6 mmol/L

Retest at intervals as suggested in cardiovascular guidelines 

 The result is normal

* When HbA1c and fasting glucose are discordant with regard to diagnosis of diabetes, repeat testing at an interval of 3-6 months is recommended.

  • The test that is above the diagnostic cut point should be repeated – if the second test remains above the diagnostic threshold then diabetes is confirmed.
  • If the second result is discordant with the first then subsequent repeat testing at intervals of 3 to 6 months is recommended. Patients with discordant results are likely to have test results near the diagnostic threshold.

References

  1. NZSSD Position statement on the diagnosis of, and screening for, type 2 diabetes. Sept 2011 New Zealand Society for the Study of Diabetes

  2. Management of type 2 diabetes. New Zealand Primary Care Handbook 2012