NZSSD Position Statement on Screening and Type 2 Diabetes

This statement is a guide for health practitioners and complements guidelines produced by the New Zealand Guidelines Group. The recommendations offered here do not fulfill the requirements of a formal screening programme which would require recall and referral systems, and full treatment services to be in place prior to implementation. Nevertheless, they provide a practical means of opportunistically identifying at risk individuals.

Background:

Screening refers to the process of identifying individuals who are likely to have a particular disease in an asymptomatic population, then confirming whether screen positive individuals do or do not have disease by undertaking diagnostic testing and providing recommended treatment accordingly. Screening for type 2 diabetes and prediabetes states is considered to be justified because of the high and apparently increasing prevalence of the conditions, [1] the convincing clinical trial evidence of reducing risk of progression from IGT to type 2 diabetes by lifestyle measures and some drug treatments [2-4] and the presumed likelihood of reducing risk of complications by early detection and treatment of those with undiagnosed diabetes. Screening for type 2 diabetes is not known to be associated with any significant physical or psychological harm. New Zealand guidelines suggest that screening for type 2 diabetes be undertaken in conjunction with cardiovascular risk assessment. [5] NZSSD supports this approach and recommends additional opportunistic case finding amongst high risk individuals in general practice and other clinical settings.

Who should be screened for diabetes:

NZSSD suggests that all those listed in table 1 should be screened for type 2 diabetes as part of a cardiovascular risk assessment. [5] In addition, NZSSD recommends undertaking opportunistic screening for type 2 diabetes, regardless of age, in those adults:

with ischaemic heart disease (angina or myocardial infarction), cerebrovascular disease or peripheral vascular disease,
on long term steroid or antipsychotic treatment,
who are obese (BMI ≥30; or BMI ≥27 for Indian subcontinent peoples), especially in those with a family history of type 2 diabetes,
with a family history of type 2 diabetes in more than one first degree relative (including adolescents)
with a history of gestational diabetes mellitus

In addition, obese children and adolescents should be screened especially if there is a family history of type 2 diabetes.

Table 1 : The age to start cardiovascular disease and diabetes risk assessment

Group	Men	Women
Asymptomatic people without known risk factors	Age 45 years	Age 55 years
Māori, Pacific and Indian subcontinent peoples*	Age 35 years	Age 45 years
People with other known cardiovascular risk factors or at high risk of developing diabetes 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) 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 (BP) ≥160/95 mm Hg, prior TC:HDL ratio ≥7 Known IGT (impaired glucose tolerance) or IFG (impaired fasting glucose) BMI ≥30 or truncal obesity (waist circumference ≥100 cm in men or ≥90 cm in women) eGFR † <60 ml/min/1.73m 2	Age 35 years	Age 45 years
People with diabetes	Annually from the time of diagnosis

* People from the Indian subcontinent = Indian, including Fijian Indian, Sri Lankan, Afghani, Bangladeshi, Nepalese, Pakistani, Tibetan.

† Estimated glomerular filtration rate (eGFR).

Reproduced with permission from: New Zealand Guidelines Group. New Zealand cardiovascular guidelines handbook: A summary resource for primary care practitioners. 2nd ed. Wellington : New Zealand Guidelines Group; 2009.

Screening tests:

A fasting venous plasma glucose measurement remains the recommended screening test. If a fasting test is not possible, or there is a possibility of incomplete fasting, a non-fasting HbA 1c is recommended. [5] A fasting glucose of ≥5.5 mmol/l, or an HbA1c >6% requires further diagnostic testing.

Frequency of screening:

Evidence regarding frequency of screening is limited. For those with a fasting venous plasma glucose <5.5mmol/l, 5-yearly screening is suggested. [5]

Table 2: What to do following the fasting venous plasma glucose result

Result	Action	Why
7.0 mmol/L or more	Repeat a fasting plasma glucose	Two results above this level, on separate occasions,* are diagnostic of diabetes and do not require an OGTT †
6.1–6.9 mmol/L	Request an OGTT †	This level is diagnostic of impaired fasting glucose. Diabetes or impaired glucose tolerance have not been excluded
5.5–6.0 mmol/L	Request an OGTT † in high-risk groups ‡	The result may be normal, but some patients will show diabetes or impaired glucose tolerance in an OGTT †
5.4 mmol/L or less	Retest in 5 years or earlier if risk factors for diabetes present	This result is normal

* The diagnosis of diabetes should always be confirmed by repeating a fasting plasma glucose on another day unless there is unequivocal hyperglycaemia with acute metabolic decompensation or obvious symptoms of thirst or polyuria.

† OGTT = Oral glucose tolerance test

‡ Non-European ethnicity, first-degree relative with diabetes, past history of gestational diabetes.

Diagnostic tests:

The diagnosis of diabetes is made on the basis of venous plasma glucose measurements (see table 3). In asymptomatic individuals, a fasting glucose >7 mmol/l, repeated on a second occasion confirms the diagnosis of diabetes. A glucose tolerance test is recommended in those with fasting glucose levels 5.5 - 7.0 mmol/l and in those with HbA1c > 6%, though with appreciably raised HbA 1c a fasting glucose often confirms the diagnosis. The place of HbA1c in making the diagnosis of diabetes remains to be clarified. In symptomatic individuals a random glucose (> 11mmol/l) is sufficient to establish the diagnosis of diabetes.

Table 3: Values of venous plasma glucose for diagnosis of diabetes mellitus and other categories of hyperglycaemia

Category	Blood test	Venous plasma glucose (mmol/L)
Diabetes mellitus	Fasting	≥7
	or 2-h post glucose load	≥11.1
	or both
Impaired glucose tolerance (IGT)	Fasting (if measured)	<7.0
Impaired glucose tolerance (IGT)	and 2-h post glucose load	≥7.8 and <11.1
Impaired fasting glycaemia (IFG)	Fasting	≥6.1 and <7.0
Impaired fasting glycaemia (IFG)	and (if measured) 2-h post glucose load	<7.8

Future screening tests:

HbA1c may come to be the preferred screening test in the future.

References:

Ministry of Health. A Portrait of Health. Key results of the 2006/07 New Zealand Health Survey. Wellington: Ministry of Health; 2008. Available online. URL:
http://www.moh.govt.nz/moh.nsf/indexmh/portrait-of-health
Tuomilehto J, Lindström J, Eriksson JG, Valle TT, Hämäläinen H, Ilanne-Parikka P, et al, for the Finnish Diabetes Prevention Study Group. Prevention of type 2 diabetes mellitus by changes in lifestyle among subjects with impaired glucose tolerance. N. Engl. J. Med., 2001; 344:1343-1350.
Knowler WC, Barrett-Connor E, Fowler SE, Hamman RF, Lachin JM, Walker EA, et al. for the Diabetes Prevention Program Research Group. Reduction in the incidence of type 2 diabetes with lifestyle intervention or metformin. N. Engl. J. Med., 2002;346:393-403.
Pan XR, Li GW, Hu YH, Wang JX, Yang WY, An ZX, et al. Effects of diet and exercise in preventing NIDDM in people with impaired glucose tolerance: The Da Qing IGT and Diabetes Study. Diabetes Care, 1997;20:537-544.
New Zealand Guidelines Group. New Zealand cardiovascular guidelines handbook: A summary resource for primary care practitioners. 2nd ed. Wellington: New Zealand Guidelines Group; 2009.