What is Diabetes?

Diabetes is a disorder characterised by a higher than normal blood glucose (sugar) level (hyperglycaemia). Blood glucose levels are normally controlled by the hormone insulin; this is produced by beta cells in the pancreas (a gland which lies just below the stomach).

Glucose, from the sugars and starches that we eat, is transported in the bloodstream. Insulin is needed for glucose to leave the bloodstream and enter the body’s cells where it is burned to provide energy. Without insulin, cells are deprived of glucose and energy, and the blood glucose level rises.

What’s covered on this page

>> Formal Classification of Diabetes Mellitus
(Next Page)

Type 1 and Type 2 Diabetes

In Type 1 diabetes, the cells that should produce insulin have been destroyed. At the moment, people with Type 1 diabetes face daily insulin injections for the remainder of their lifetime.

In Type 2 diabetes, which is far more common, the body doesn’t respond properly to insulin, and often not enough insulin is produced. People with Type 2 diabetes may require only a controlled diet, combined with increased levels of activity to promote weight loss, but often tablets are prescribed as well. Many people with Type 2 diabetes eventually go on to need insulin injections.

A comparison of Type 1 and Type 2 diabetes

  Type 1

  Type 2


May include the following: frequent urination, thirst, weight loss, extreme fatigue, acetone breath, nausea and vomiting, blurred vision and itchiness in the genital area. Symptoms tend to develop more gradually in Type 2 and are usually less severe.


Apparent rapid onset of symptoms (weeks)

Usually <20 yrs
High blood glucose

Develops slowly (often over years) and symptoms may go unnoticed
Usually >40 yrs
Moderately increased blood glucose
Often overweight


In most cases, the body is prompted to turn against itself and destroys the beta cells which produce insulin.

This is brought about by cells of the immune system which should only respond to foreign invaders, and is known as an ‘autoimmune response’.

Insulin is produced but the body does not  respond properly to it. This is known as ‘insulin resistance’.  Often insufficient insulin is produced to cope with the body’s requirements.


Insulin injections and a diet regimen. Diet and exercise regimen.
Tablets are often also required.
Often insulin injections are needed, later on in life.


A word about the terminology:

Type 1 diabetes is often referred to as insulin-dependent (IDDM) or juvenile-onset diabetes. Type 2 diabetes is often referred to as non-insulin dependent (NIDDM) or maturity-onset diabetes. People with NIDDM may require insulin treatment later on, so this is confusing terminology. The use of ‘juvenile onset’ and ‘maturity’ or ‘adult onset’ has diminished as we have learned more of the biology of the two types of diabetes. Defining diabetes as ‘Type 1’ or ‘Type 2’ according to the cause, as opposed to ‘IDDM’ or ‘NIDDM’ according to the treatment, is the most acceptable classification.

Other Types of Diabetes

Gestational Diabetes (GDM)

Pregnant women often develop diabetes. During pregnancy large quantities of hormones are produced; these hormones may reduce insulin action in the mother’s body, causing insulin resistance (similar to Type 2 diabetes). Treatment for gestational diabetes consists of diet and, sometimes, insulin therapy. The diabetes usually disappears after the baby is born, but many women do then develop Type 2 diabetes later on in their lives.


Latent Autoimmune Diabetes in Adults. It is becoming evident that a proportion of adults may have a slowly evolving kind of Type 1 diabetes, which is characterised by the presence of autoantibodies. Some people diagnosed with Type 2 diabetes soon find themselves dependent on insulin; these people may actually have a slowly progressive form of Type 1 diabetes or LADA.


Maturity Onset Diabetes of the Young. This is a rarer form of diabetes – a non insulin dependent condition which is diagnosed in young people. There is usually a clear pattern of dominant inheritance in MODY patients and investigation of this genetically defined subgroup of Type 2 diabetes has so far revealed more than six different genetic causes.


Maternally Inherited Diabetes and Deafness has been identified as another less common subtype of diabetes, which is genetically defined.

Other specific forms

Some other specific forms or causes of diabetes are given below:

  • Drug or chemical induced (includes steroids, thyroid hormone and ‘adrenergic agonists’
  • Pancreatitis and other disease of the pancreas
  • Diabetes is associated with some other diseases or syndromes, including:
    • Syndrome X
    • Cushing’s Syndrome
    • Hyperthyroidism
    • Haemochromatosis
    • Leprechaunism
    • Cystic Fibrosis
    • ‘Stiff man’ Syndrome
    • Other genetic syndromes

Diabetes occurring in such circumstances is often referred to as ‘secondary diabetes‘. In many instances though, there may be an existing tendency towards diabetes anyway; drugs or diseases, a few of which are mentioned above, then effectively act as an environmental stimulus, ‘unmasking’ the diabetes.

Some forms of secondary diabetes result in a lack of insulin and are similar, in many respects, to Type 1 diabetes. Others are associated with insulin resistance and show parallels with what we describe as Type 2 diabetes.

For a formal classification of diabetes, see Page 2

Diagnosing Diabetes

Criteria for the diagnosis of diabetes have been described by the American Diabetes Association (1) and WHO (2)  and are widely adopted.

The use of HbA1c for diagnosing Type 2 diabetes has now been approved in New Zealand. It is now the tool of choice for opportunistic screening with advantages including:

  • No need for fasting
  • HbA1c is less afected by day-to-day variation in blood glucose levels
  • Reduced biological variability (therefore fewer false positives and negatives with HbA1c testing compared to plasma glucose testing)
  • Simpler laboratory requirements

Although HbA1c testing is expensive, since the long term consequences of undiagnosed diabetes are also expensive this cost is offset by (hopefully) savings made further down the line. Forward thinking!

Criteria for the diagnosis of diabetes mellitus

Symptoms of diabetes plus random plasma glucose > 11.1 mmol/l


Fasting Plasma Glucose (FPG) > 7.0 mmol/l


Oral Glucose Tolerance Test (OGTT) 2-hr post glucose load > 11.1 mmol/l


HbA1c test > 48 mmol/mol (6.5%) *see note below


In the absence of symptoms two separate diagnostic tests are recommended.

All tests should be performed in an accredited laboratory. This means that point-of-care testing – whilst useful – cannot be used definitively for diagnosis.

*HbA1c is unsuitable as a diagnostic tool in certain circumstances including:

    • For the diagnosis of Type 1 diabetes
    • For the diagnosis of diabetes in pregnancy (see ‘Gestational Diabetes‘ below)
    • In patients who are acutely unwell


  • In patients who have had diabetes symptoms for less than 2 months
  • In patients with certain haemoglobinopathies or anaemias (see section on HbA1c)


Pre-diabetes and Impaired Glucose Tolerance

In the context of Type 2 diabetes, it is important to point out that there is an intermediate between the “definitely diabetic” and “definitely not diabetic” states. The term ‘borderline diabetes‘ has been used to describe this. Many will vehemently cry that surely you either have diabetes or you do not; but unfortunately there is a grey area…

The term ‘glucose tolerance‘ describes the ability of the body to keep blood glucose levels within the normal range. There is a grey area within the diagnostic criteria for diabetes in which people with ‘not-quite-normal’ glucose tolerance fall. Such people are said to have ‘impaired glucose tolerance’, or IGT. Some may go on to develop full blown diabetes, others may not. People with IGT are also at risk of developing diabetes related complications.

Another term sometimes used is ‘impaired fasting glucose’ or IFG. This describes the borderline condition in which fasting blood glucose levels are slightly high.

Recently, IGT and IFG have both been reclassified as ‘pre-diabetes‘. People with ‘pre-diabetes’ are at high risk of developing diabetes.

Identifying ‘Pre-diabetes’

Method of testing FPG OGTT  HbA1c
Normal < 5.6 mmol/l 2-hr post glucose load <7.8 mmol/l < 5.7%
<39 mmol/mol
Pre-diabetes 5.6 – 6.9 mmol/l 2-hr post glucose load
7.8 – 11.1 mmol/l
5.7 – 6.5%
39 – 48 mmol/mol
Diabetes > 7.0 mmol/l 2-hr post glucose load
> 11.1 mmol/l
> 6.5%
> 48 mmol/mol



Diagnosis of Gestational Diabetes

Diagnosis of diabetes in pregnancy – Gestational DIabetes or GDM – has slightly different criteria; the text below has been taken from the MOH Clinical Practice Guideline (3)

Early pregnancy

Universal screening using glycated haemoglobin (HbA1c), as part of ‘booking’ antenatal blood tests (ideally before 20 weeks), will identify women with probable undiagnosed diabetes or prediabetes. Women with an HbA1c ≥ 50 mmol/mol should be under the care of a service that specialises in diabetes in pregnancy. Women with HbA1c values in the range of 41–49 mmol/mol should be offered the diagnostic oral glucose tolerance test at 24–28 weeks as they are at an increased risk of gestational diabetes. Some local policies currently treat women with HbA1c values in the range of 41–49 mmol/mol.

At 24–28 weeks’ gestation

At 24–28 weeks’ gestation, all women not previously diagnosed with diabetes who are at high risk of gestational diabetes (HbA1c of 41–49 mmol/mol) should be offered the diagnostic two-hour, 75 g oral glucose tolerance test. (If fasting glucose ≥ 5.5 mmol/L or two-hour value ≥ 9.0 mmol/L, refer to services that specialise in diabetes in pregnancy.) All other women should be offered screening for gestational diabetes using the one-hour, 50 g, oral glucose challenge test known as the polycose test. (If glucose ≥ 11.1 mmol/L, refer directly to services that specialise in diabetes in pregnancy without further testing; if glucose ≥ 7.8–11.0 mmol/L, arrange a 75 g, two-hour oral glucose tolerance test (OGTT) without delay). Offer enrolment in the randomised trial of different diagnostic criteria. For further details of the New Zealand GEMS Trial contact gems@auckland.ac.nz or go to www.ligginstrials.org/GEMS

Metabolic Syndrome

Metabolic syndrome is a term often used in relation to diabetes and heart disease. It refers to the cluster of conditions that are the most dangerous of the heart attack risk factors.

  • A quarter of the world’s adults have metabolic syndrome
  • People with metabolic syndrome are twice as likely to die from, and three times as likely to have a heart attack or stroke compared with people without the syndrome
  • People with metabolic syndrome have a five-fold greater risk of developing type 2 diabetes
  • Up to 80% of the 200 million people with diabetes globally will die of cardiovascular disease
  • This puts metabolic syndrome and diabetes way ahead of HIV/AIDS in morbidity and mortality terms yet the problem is not as well recognised

Earlier diagnosis is needed to stop this global time bomb. This new International Diabetes Federation (IDF) Worldwide Definition of the Metabolic Syndrome provides physicians with the tools to quickly identify those at risk and also to compare the impact across nations and ethnic groups. The new IDF worldwide definition was developed during a unique consensus workshop

According to the new IDF definition, for a person to be defined as having the metabolic syndrome they must have the following:

Central obesity (defined as waist circumference ≥ 94cm for Europid men and ≥ 80cm for Europid women, with ethnicity specific values for other groups) plus any two of the following four factors:

Raised TG level: ≥ 150 mg/dL (1.7 mmol/L), or specific treatment for this
lipid abnormality
Reduced HDL cholesterol: < 40 mg/dL (1.03 mmol/L*) in males and < 50
mg/dL (1.29 mmol/L*) in females, or specific treatment for this lipid
Raised blood pressure: systolic BP ≥ 130 or diastolic BP ≥ 85 mm Hg, or
treatment of previously diagnosed hypertension
Raised fasting plasma glucose (FPG) ≥ 100 mg/dL (5.6 mmol/L), or
previously diagnosed type 2 diabetes

If above 5.6 mmol/L or 100 mg/dL, OGTT is strongly recommended but is not
necessary to define presence of the syndrome.

The Effects of High Blood Glucose Levels

When blood passes through the filtering system in the kidneys, glucose is normally retained; but when the blood glucose level rises too high, glucose ‘spills over’ into the urine. This makes the urine so concentrated that extra water is drawn out too. People with untreated diabetes therefore produce large volumes of urine, becoming dehydrated and very thirsty. Fungal infections (such as thrush) thrive in the moist sugary environment of the genital area and can prove to be a persistent problem in people with diabetes.

In the absence of insulin, the body’s cells are not able to take glucose from the bloodstream. Messages are sent to the liver to release glucose from its stores because the cells believe that the body is in starvation. The blood glucose level rises… In desperation, cells turn to fats as a fuel instead. Burning up fats yields chemicals known as ketones. If these are produced faster than they can be disposed of by the body, they build up in the bloodstream and become toxic. Ketones make the blood too acidic and messages are sent from the brain to the lungs to breathe faster. You can smell ketones on the breath – fruity, like pear drops. If left untreated then vomiting, drowsiness and eventually coma will result. This life-threatening state is called diabetic ketoacidosis or DKA. It is usually only a potential problem for people with Type 1 diabetes.

Prolonged severe high blood glucose levels in people with Type 2 diabetes may lead to a condition known as ‘hyperosmolar non-ketotic coma‘ (HONK). This is caused by extreme loss of fluid (dehydration) and the resulting chemical imbalance in the blood.

Over a period of years, high blood glucose levels can cause damage to numerous body tissues, including the eyes, nerves, kidneys and heart. These ‘complications’ are chiefly the result of damaged blood vessels.

Treatments for Diabetes

Treatments for diabetes depend on the individual person and the type of diabetes. The aim of treatment is to keep blood glucose levels as near normal as possible.

Treatment for controlling blood glucose levels may consist of one of the following approaches:

  • Diet and Exercise (T2DM, GDM)
  • Diet and Exercise and Tablets (T2DM)
  • Diet and Exercise and Tablets and Insulin (T2DM)
  • Diet and Exercise and Insulin (T1DM, T2DM, GDM)

Daily finger-prick blood glucose testing is necessary and this is a tool that can be used to make your treatment work for you.

However, none of these treatment approaches work on a prescriptive basis. Successful diabetes therapy involves your conscious input from one day to the next, for the rest of your life. For this reason, your diabetes treatment will need to be complemented by your diabetes management or ‘self-care’ skills.

The appropriate treatment, plus good day-to-day diabetes management should help you to achieve good diabetes control.

Here, we outline the basic principles behind the different treatment approaches. There is more detailed information on the different aspects of diabetes treatment in the “Diabetes Management” section.

Type 1 Diabetes (T1DM)

If you have Type 1 diabetes then your body will not be producing any insulin. Insulin is necessary for survival, so the only option is to provide the body with insulin from an outside source. Because it is a protein hormone, if it is taken by mouth (e.g. as a tablet) it is destroyed by the digestive system before it has chance to be absorbed. Insulin is therefore injected into the layer of fat that lies just beneath the skin. Alternatively, insulin can be supplied continuously by a pump; it is fed into the body through a long thin tube with a needle or plastic cannula that is inserted under the skin.

The amount of insulin that is given must closely match the body’s requirements in order to keep the blood glucose level in the right range. Too much insulin causes it to fall too low (hypoglycaemia) and too little causes it to rise too high (hyperglycaemia). Both of these conditions are unpleasant and can be dangerous if they are not corrected.

So, insulin needs to be closely matched with food intake (amount and timing) and exercise levels. This continual juggling act forms the crux of diabetes management and is only made possible with regular testing of blood glucose levels during the day.

Type 2 Diabetes (T2DM)

If you have Type 2 diabetes, your treatment will depend on a number of factors, including:

  • Your body weight
  • Your current eating habits
  • Your current level of physical activity
  • The severity of your symptoms
  • Your blood glucose levels
  • How long you have had diabetes for

You may at first be advised to make changes in your lifestyle – lose some weight and increase your level of physical activity, for example. Weight loss and exercise can be very successful in getting blood glucose levels back down to the normal range. Although it can be very difficult to change habits of a lifetime, the threat of your health deteriorating further may signify that now is the time to stop and take stock of things.

In some people, the ‘diet and exercise’ approach is simply not enough to bring blood glucose levels into line and extra help is needed. Usually the next step is tablets – known as oral hypoglycaemics – that either help you to produce more insulin, or help your body to use the insulin more effectively. These tablets, however, are only effective if your body is able to produce some insulin. You may be prescribed more than one type of tablet. You should remember that diet, weight loss and exercise are still crucial to the diabetes management plan even when tablets are prescribed.

Some people with Type 2 diabetes need insulin injections. This might be temporary – if your body is under a lot of stress, you have an infection or you have been admitted to hospital for surgery, for example. However, in many cases, Type 2 diabetes is a progressive condition in which insulin production declines slowly over the years. Eventually, not enough insulin is produced and then there is no alternative but to start on injections. If this happens to you then you must remember that this is not a failing on your part – it is just the natural progression of things.

Regardless of the treatment approach, people with Type 2 diabetes should ideally test blood glucose levels on a day-to-day basis. It is only with this information that you can assess the effects of your daily activities on your blood glucose level.

Gestational Diabetes (GDM)

The aim of treatment in Gestational diabetes is to bring blood glucose levels into the normal range in order to prevent complications of the pregnancy.

Dietary therapy is usually the first line of treatment. Refined foods and simple sugars should be replaced with more complex carbohydrates and fat intake should be reduced. A moderate restriction in calorie intake and increased exercise are generally recommended in overweight women.

In some women, modifying the diet is not sufficient to bring blood glucose levels down. In such cases, insulin injections are required.

The effectiveness of your diabetes management will largely be down to the choices that you make on a daily basis. Diabetes Info NZ aims to provide you with the information and tools to enable you to make the right choices.


Explore this section Introducing Diabetes:

What is Diabetes?  |  Causes of Diabetes  |  Long Term Complications  |  Managing Diabetes