Also Known As
Diabetes mellitus
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This article waslast modified on 24 October 2018.
What is it?

Note: This article addresses diabetes mellitus, not diabetes insipidus. Although the two share the same reference term "diabetes" (which means increased urine production), diabetes insipidus is much rarer and has a different underlying cause.

Diabetes mellitus is a condition in which the level of glucose (sugar) in an individual's blood becomes too high because the body cannot use it properly. This results either from an inability to produce insulin or because the individual's body has become resistant to the insulin produced. About 2.8 million people in the United Kingdom (4.45% of the population) are known to have diabetes and a further ¾ million may have the condition and not know it. Insulin is a hormone, produced by beta cells of the pancreas, which controls the movement of glucose into most of the body's cells and maintains blood glucose levels within a narrow concentration range. Most tissues in the body rely on glucose for energy production, and all but a few - such as the brain and nervous system - are entirely reliant on insulin to deliver this essential fuel. Diabetes disrupts the normal balance between insulin and glucose. Usually after a meal, carbohydrates are broken down into glucose and other simple sugars. This causes blood glucose levels to rise and stimulates the pancreas to release insulin into the bloodstream. Insulin allows glucose into the cells, where it also promotes storage of excess glucose - either as glycogen in the liver or as triglycerides in adipose (fat) cells.
If there is insufficient or ineffective insulin, glucose levels remain high in the bloodstream and the body's cells "starve." Since glucose is not available to the cells with severe insulin deficiency, the body may attempt to provide an alternate energy source by breakind down fatty acids from fat cells. This less efficient process leads to a build-up of ketones (by-products that result from the use of fat as an alternative energy source when glucose is unavailable) and upsets the body’s acid-base balance, producing a state known as ketoacidosis.
This can cause both short term and long term problems depending on the severity of the imbalance. In the short term it can upset the body's electrolyte balance, causing dehydration as high blood glucose levels increase the amount of urine produced. If unchecked, this can eventually lead to loss of consciousness, kidney failure and death. In the longer term, sustained high glucose levels can damage blood vessels, nerves, and organs throughout the body, contributing to other problems such as high blood pressure, heart disease, kidney failure and loss of vision in addition to diabetes.


Accordion Title
About Diabetes
  • Types of Diabetes

    There are two main types of diabetes: Type 1 (which used to be called insulin dependent diabetes or juvenile onset diabetes) and Type 2 (which used to known as non-insulin dependent diabetes or adult onset diabetes). In addition, Gestational Diabetes is a term used to describe diabetes which is recognised for the first time during pregnancy. Pancreatic disease or damage can also cause diabetes if the insulin producing beta cells are destroyed.

    Type 1 diabetes develops if the body can no longer produce insulin. It accounts for approximately 10% of diabetes cases in the United Kingdom and is usually diagnosed in those under the age of 30. Symptoms often develop abruptly and the diagnosis is often made following an emergency admission to hospital. The patient may be seriously ill, even unconscious, with very high glucose levels and high levels of ketones.
    Patients with Type 1 diabetes make very little or no insulin. Any insulin producing beta cells that patients have at the time of diagnosis are usually completely destroyed within 5 to 10 years leaving them entirely reliant on insulin injections. The exact cause of type 1 diabetes is unknown, but a family history of diabetes, viruses that injure the pancreas, and autoimmune processes (where the body's own immune system destroys the beta cells) are all thought to play a role. As type 1 diabetes has an earlier age of onset and hence longer duration, patients may have more severe medical complications than other forms of diabetes. For instance, currently 40% of those with type 1 diabetes develop serious kidney problems leading to kidney failure by the age of 50.

    Those with Type 2 diabetes do make their own insulin but it is either not in a sufficient amount to meet their needs and/or their body has become resistant to its effects. At the time of diagnosis they may have typical symptoms of diabetes, especially thirst, weight loss or may be passing large amounts of urine or they may not have any symptoms, and diagnosis may be made on finding high glucose concentrations in the blood. About 90% of diabetes cases in the United Kingdom are type 2. It generally occurs later in life, in those who are obese, sedentary and over 45 years of age. Risk factors include:

    • Weight excess / obesity
    • Lack of exercise
    • A family history of diabetes
    • Any abnormality of glucose tolerance – the oral glucose tolerance test (OGTT) may identify individuals whose ability to handle a high glucose meal is not normal but is not sufficiently abnormal to identify them as Diabetic
    • Ethnic groups - more common in Asian and African-Caribbean communities
    • Gestational diabetes during pregnancy or baby weighing more than 9 pounds
    • High blood pressure
    • High triglycerides, high cholesterol, low HDL

    Because the population of the western world is becoming more obese and not getting enough regular exercise, the number of those developing type 2 diabetes is rising and, of particular concern is its development in young people.

    Gestational diabetes is usually a temporary type of hyperglycaemia (high blood glucose concentration) seen in some pregnant women, usually during the second or third trimester. The cause is unknown, but it is thought that some hormones from the placenta increase insulin resistance in the mother causing elevated blood glucose levels. In the UK, gestational diabetes is usually diagnosed by an oral glucose tolerance test carried out, either because high glucose concentrations have been found in the urine or blood or because the women is known to be at risk for the condition (obesity, a family history of Type 2 diabetes, an unexplained stillbirth or neonatal death in a previous pregnancy, a very large infant in the current or a previous pregnancy). Testing is usually performed between the 24th and 28th week of pregnancy. If gestational diabetes is not treated, the baby is likely to be larger than normal, be born with low glucose levels, and be born prematurely. Gestational diabetes also raises the risk of eventually developing type 2 diabetes, for both the mother and the baby.

    Impaired fasting glycaemia or impaired glucose tolerance (sometimes referred to as "pre-diabetes") are conditions which can only be detected by use of the oral glucose tolerance test and are characterised by glucose levels that are higher than normal, but not high enough to be diagnostic of diabetes. Usually these individuals do not have any symptoms but if nothing is done to lower their glucose levels, they are at great risk of developing diabetes in the future. Recognising these conditions is important as recent evidence shows that progression to diabetes can be markedly reduced by simple measures such as weight loss and increased exercise.


  • Signs and Symptoms

    The signs and symptoms of diabetes are related to high glucose levels (hyperglycaemia), temporarily low glucose levels (hypoglycaemia), and to complications associated with diabetes. The complications can be related to lipid (fat) production, to macrovascular (large blood vessel) or microvascular (small blood vessel) damage, to organ damage - for example kidney (diabetic nephropathy), nerve (diabetic neuropathy), and eye (diabetic retinopathy) damage, and/or to the slower healing associated with diabetes. Patients with Type 1 diabetes are often diagnosed with acute severe symptoms that require hospitalisation. With early type 2 diabetes, and gestational diabetes there may be no symptoms.

    Symptoms of type 1 and type 2 diabetes with hyperglycaemia may include any of:

    • Increased thirst
    • Passing increasing amounts of urine
    • Increased appetite (with type 1 weight loss is also seen)
    • Tiredness
    • Feeling sick
    • Vomiting
    • Stomach pain (especially in children)
    • Blurred vision
    • Slow-healing infections
    • Numbness, tingling, and pain in the feet
    • Erectile dysfunction in men
    • Absence of menstruation in women
    • Rapid breathing (acute)
    • Decreased consciousness, coma (acute)

    Symptoms of impending hypoglycaemia:
    Temporary hypoglycaemia in the diabetic patient may be caused by the accidental injection of too much insulin, not eating enough or waiting too long to eat, exercising strenuously, or by the swings in glucose levels seen in patients with diabetes which is difficult to control (often referred to as 'brittle diabetes'). Hypoglycaemia needs to be treated because, if it is severe, it can rapidly progress to unconsciousness. True hypoglycaemia occurs when the blood sugar is below 2.5 mmol/L, though symptoms may develop earlier, especially if the blood sugar falls rapidly, and include:

    • Sensation of hunger
    • Headache
    • Anxiety
    • Sweating
    • Confusion
    • Trembling
    • Weakness
    • Double vision
    • Convulsions (severe)
    • Coma (severe)


  • Tests

    Diabetes is diagnosed by measurement of glucose in blood (or more correctly in plasma which is the fluid left behind when cells have been removed from blood) in accordance with the criteria of the World Health Organisation.
    Either random or fasting measurements or the measurements made during an oral glucose tolerance test (OGTT) may be used. The OGTT involves a fasting glucose, followed by the patient drinking a standard amount of a glucose solution to "challenge" their system, followed by another glucose blood test two hours later.
    In an individual with typical symptoms, diabetes is diagnosed by finding either a random plasma glucose concentration greater than 11.0 mmol/L or a fasting plasma glucose concentration greater than 7.0 mmol/L or a plasma glucose concentration greater than 11.0 mmol/L two hours after taking 75g of anhydrous glucose in an OGTT. HbA1c (also called haemoglobin A1c or glycohaemoglobin) evaluates the average amount of glucose in the blood over the last 2 to 3 months and has been recommended more recently as another test to screen for diabetes.
    In the absence of typical symptoms, diagnosis should not be based on a single glucose measurement but requires confirmation by at least one further glucose test result on another day with a value in the diabetic range. If the fasting or random glucose concentrations do not fall into the criteria given above then an oral glucose tolerance test should be performed. Gestational diabetes (GDM) is diagnosed by an OGTT, undertaken in a woman at risk for GDM.
    Sometimes random urines are tested for glucose, protein, and ketones during a routine clinical examination using a 'dipstick test'. If glucose and/or protein or ketones is present on the dipped indicator strip then further investigations are necessary. This screening tool is not sensitive enough for monitoring patients who have been diagnosed as diabetic.
    Patients with diabetes can monitor their condition by measuring their own blood glucose level. Home blood measurements are done by placing a drop of blood, obtained by pricking the finger with a small lancet device, onto a plastic glucose test strip and then inserting the strip into a small test meter, which provides a digital readout of the blood glucose concentration. Glucose measurements can be made several times a day at a frequency which depends on how well their blood glucose concentration is controlled.

    Several laboratory tests may be used to monitor diabetes on a regular basis.

    To monitor glucose control:
    Glucose, Haemoglobin A1c (HbA1c)

    To monitor kidney function:
    Creatinine, Creatinine Clearance, Microalbuminuria  (A test which detects very small quantities of albumin in the urine and can indicate early kidney damage.  It is measured as the Albumin Creatinine ratio (ACR) or Albumin Excretion rate)

    To monitor lipids:
    Triglycerides, cholesterol, HDL cholesterol, LDL cholesterol.


  • Treatment

    While there is no way to prevent type 1 diabetes, the risk of having type 2 diabetes can be greatly decreased by losing excess weight, exercising and by eating a healthy diet with limited fat intake. By identifying pre-diabetic conditions and making the necessary lifestyle changes to lower glucose levels to normal levels you may be able to prevent type 2 diabetes or delay its onset by several years.  Normalising blood glucose can also minimise or prevent vascular and kidney damage.

    There is currently no cure for diabetes (although there has been some success with transplants including islet (beta) cell transplantations as a way to restore insulin production). The goals of diabetes treatment are to keep glucose levels close to normal and to treat any progressive vascular disease or organ damage that arises.
    Treatment of diabetes at the time of diagnosis may be very different to that required afterwards.

    Type 1 diabetes may be diagnosed following a short term illness - patients may have very high blood glucose levels, electrolytes out of balance, be in a state of diabetic ketoacidosis (where their body has tried to break down fats to use as an alternate fuel source, leading to the toxic build up of ketones in the blood) with some degree of kidney failure. They may have become unconscious and comatose. This is a serious condition requiring immediate hospitalisation and expert care to get the body back to its normal balance.

    Patients with Type 2 diabetes may occasionally be sick in a similar way to that described for those with type 1 diabetes. This may occur if they have ignored initial symptoms, if they have neglected their regular treatment, or if they have a serious stress to their system such as a heart attack, stroke or an infection. Very high blood glucose levels and dehydration reinforce each other, leading to weakness, confusion, convulsions, and to hyperglycaemic hyperosmolar (highly concentrated blood) coma. This is also a serious condition requiring immediate admission to hospital.
    Ongoing treatment involves daily glucose monitoring and control, eating a healthy planned diet, and exercising regularly (to lower glucose levels in the blood, increase the body's sensitivity to insulin, and to increase blood circulation). It is important to work closely with your doctor or diabetes nurse and have regular checks that can include monitoring tests such as microalbuminuria, haemoglobin HbA1c, lipids and tests of kidney function in addition to blood pressure, eye and foot tests. Immediate attention is required for complications such as:

    • Wound infections, especially on the feet. They are slow to heal and if not adequately treated could eventually lead to amputation. Aggressive and specialised measures are often necessary
    • Vision problems, diabetic retinopathy can lead to eye damage, a detached retina, and to blindness. Laser surgery may be necessary
    • Urinary tract infections which may be frequent and resistant to antibiotic treatment

    Type 1 diabetic patients must self check their blood glucose levels and inject themselves with insulin from once to several times a day. (Insulin is not available in an oral form, it breaks down in the stomach so it must be injected under the skin). For some, a similar amount of insulin is taken every day; others prefer a more flexible regime where the amount and type of insulin injected is adjusted to take into account what they are eating, the size of their meals, and the amount of activity they are getting. There are several types of insulin available, some are fast acting and short lived while others take longer to act but have a longer duration.
    Most patients with type 1 diabetes use a combination of insulins to meet their needs, and maintaining control can sometimes be a challenge. Stress, illnesses, and infections can alter the amount of insulin necessary, and some patients have "brittle" control - where glucose levels makes rapid swings during the day. A number wear insulin pumps, programmable devices that are carried at the waist and provide small amounts of insulin (through a needle under the skin) throughout the day to more closely match normal insulin secretion. As another complicating factor, type 1 diabetic patients may develop antibodies to insulin over time, their body begins to identify the injections as an "intruder" and works to destroy the insulin, resulting in the necessity of higher doses of insulin or of switching to a different kind.
    Patients may also "overshoot," running into trouble with low glucose levels (hypoglycaemia or "hypos") if they inject too much insulin, go extended periods of time without eating, or if their needs change unexpectedly. They must carry glucose with them, in the form of tablets or sweets and be ready to take some at the first signs of hypoglycaemia (low blood sugar). Carrying glucagon injections is also recommended for times when their hypoglycaemia is not responding to oral glucose or for someone else to give them if they have become unconscious. Glucagon is a hormone which counter-acts the action of insulin and increases glucose concentrations. Acute conditions, such as diabetic ketoacidosis or renal failure, may require admission to hospital to resolve.

    Type 2 diabetic patients usually monitor control either by blood glucose measurements or testing urine for the presence of glucose. Patients range from those who can control their glucose levels with diet and exercise, through those who require oral medicines, to those who need to take daily insulin injections. Many will move along through this range as their disease progresses. The oral medicines fall into three groups, those that stimulate the pancreas to produce more insulin, those that help make the body more sensitive to the insulin it is producing, and those that slow the absorption of carbohydrates in the stomach (slowing down the increase in blood glucose after a meal). Type 2 diabetics often take 2 or more of these medicines, and/or insulin injections - whatever it takes to achieve glucose control.

    With gestational diabetes, the mother-to-be will need to eat a modified diet, get regular exercise, and monitor glucose regularly. If more control is needed, she will be given insulin injections (at this time oral medications are not used). Usually diabetic symptoms will decrease after birth, although the woman remains at a higher risk of developing type 2 diabetes and she should be carefully monitored with any subsequent pregnancies. Soon after birth her baby will be monitored for signs of hypoglycaemia and for any breathing distress.