Until recently type 2 diabetes was often discovered using a urine dipstick test when a person began to experience symptoms. In recent years, screening for type 2 diabetes has been expanded and now it is more often diagnosed using a blood test before any symptoms develop.

Type 1 diabetes symptoms normally develop very rapidly, sometimes over a couple of weeks. They tend to be more severe. Some 23% of type 1 diagnoses occur when the person presents in diabetic ketoacidosis. Type 2 diabetes symptoms are normally milder and develop gradually. These symptoms are caused by the effect of raised blood glucose levels on the body.

If the level of glucose in the blood becomes too high, excess glucose is removed from the blood by the kidneys and excreted via the urine (glycosuria). This results in greater urine production and causes the patient to urinate frequently. This may also lead to frequent episodes of thrush. Water held in the cells is required to replace lost blood volume and further causes dehydration and thirst.

Symptoms of type 1 diabetes:

• polyuria - the need to urinate frequently
• polydipsia - increased thirst & fluid intake
• polyphagia - increased appetite
• weight loss
• tiredness.

Other major symptoms include:

Blurred vision: a change in glucose absorption can bring about a change in the shape of the lens in the eye, leading to an altered vision quality. This can cause blurred vision, a common complaint that can indicate type 1 or type 2 diabetes.

Diabetic ketoacidosis: diabetic ketoacidosis occurs when the body begins to break down stores of fat as an alternative source of energy, leading to a build-up of acids in the blood known as ketones. This can result in weight loss and muscle wasting. Diabetic ketoacidosis is a rare and acute complication of diabetes, often requiring admission to ITU / HDU. Diabetic Ketoacidosis can result in coma and possibly death if left untreated. Symptoms of type 1 diabetes can develop quickly, over weeks or even days.

Symptoms of type 2 diabetes:

In type 2 diabetes the signs and symptoms are not always obvious as the condition usually develops slowly over a period of years. It may only be picked up in a routine medical check-up. The common symptoms are:

• tiredness
• poor healing process
• malaise
• sometimes weight gain or weight loss
• thirsty and nocturia
• dry mouth.

Thirst and polyuria will develop as hyperglycaemia progresses, particularly in the elderly. It is important to be vigilant for the signs and symptoms of diabetes as early diagnosis and treatment can reduce the risk of developing complications later. Many people have type 2 diabetes for years without knowing it because early symptoms can be general.

Useful resources

• Diabetes UK. Type 1 diabetes symptoms
• Diabetes UK. Type 2 diabetes symptoms

If you or your patient suspects that these symptoms may indicate diabetes then it needs to be correctly diagnosed before treatment can be given. It is important to be vigilant for the signs and symptoms of diabetes and non-diabetic hyperglycaemia when treating patients, and to diagnose as early as possible so that treatment can be started. In the case of NDH, early diagnosis could mean that type 2 diabetes can be prevented. Once somebody is diagnosed with diabetes, they should be entered onto their GPs diabetes register to ensure they begin the diabetes care pathway.

A range of diagnostic approaches are outlined below:

HbA1c

Glycated haemoglobin is the chemical that carries oxygen in red blood cells, which also has glucose attached to it. It differs from a blood glucose level as it provides a longer-term average reading (approximately three months – the lifespan of a red blood cell). The HbA1c test is usually done in hospital or a GP clinic and then sent to a laboratory and is usually checked at three to six monthly intervals depending on patient requirements. Increasingly, instant readings may be obtained at new ‘point of care’ testing stations.

HbA1c has become the most common method of diagnosing diabetes, as recommended by the World Health Organization (WHO). It primarily measures the levels of HbA1c in the blood to identify the average plasma glucose concentration over the previous six to twelve weeks. The test measures a part of the amount of blood glucose attached to haemoglobin. The test gives a good indication of an average blood glucose control as it reflects periods of higher blood glucose, for example, following meals and periods of lower blood glucose, for example, following exercise.

A blood sample is required. An HbA1c of 48mmol/l (6.5%) or more is a diagnosis of diabetes in most situations. HbA1c is also used to monitor diabetes in a patient and will normally be done every three to six months depending on patient requirements. Patients with diabetes aim to lower the HbA1c level to below a target level, normally around 48-53 mmol/mol (6.5% - 7.0%, NICE guidelines 2018). However, individualisation of the target goal level will be negotiated between the patient and their diabetes team as the levels may vary for each patient, e.g. in the elderly and frail. Attempting to maintain a low HbA1c may place an elderly or frail patient at risk of hypoglycaemia and falls.

A blood sample is required. An HbA1c of 48mmol/l (6.5%) or more is a diagnosis of diabetes in most situations. HbA1c is also used to monitor diabetes in a patient and will normally be done every three to six months depending on patient requirements. Patients with diabetes aim to lower the HbA1c level to below a target level, normally around 48-53 mmol/mol (6.5% - 7.0%, NICE guidelines 2018). However, individualisation of the target goal level will be negotiated between the patient and their diabetes team as the levels may vary for each patient, e.g. in the elderly and frail. Attempting to maintain a low HbA1c may place an elderly or frail patient at risk of hypoglycaemia and falls.

When it cannot be used:

• children and young people
• if patient is suspected of having type 1 diabetes
• patients has symptoms of diabetes for less than two months
• patients who are acutely ill
• if patient is taking medication that may cause rapid glucose rise, for example steroids
• patient has acute pancreatic damage, including pancreatic surgery
• pregnancy
• patients with abnormal red blood cells such as Thalassaemia.

Random blood glucose test

In certain cases, a blood glucose reading can be used to measure the glucose, usually via a finger prick blood test, with no consideration to when the last meal was eaten. A level of 11.1 mmol/L or more in the blood sample indicates diabetes. A further blood glucose test will need to be done to confirm the diagnosis.

Fasting blood glucose test (FBG)

The FBG test is taken using a blood sample obtained following a period of fasting (so no food or drink, except water) of at least eight hours. The fast normally starts from midnight. A sample of blood is taken early the next day, before food or drink. A level of 7.0 mmol/L or more after an overnight fast indicates diabetes. To confirm the diagnosis, it is usually necessary to repeat the test a second time on a different day.

Oral glucose tolerance test (OGTT)

For this test the patient fasts from midnight and then a baseline fasting blood glucose test is taken. The patient then consumes a drink that contains 75g of glucose’ - recent reductions in the sugar content of certain drinks should be checked to ensure the correct dose is administered – recent reductions in the sugar content of certain drinks should be checked to ensure the correct dose is administered. Two hours later the blood glucose level is measured again. This test is different from the others as the patient drinks a sugary drink as a way of measuring how effectively the pancreas secretes insulin to manage the glucose load. In a person without diabetes glucose levels rise and fall quickly, as the body naturally produces insulin to lower the blood glucose. A person with diabetes will see a sharp rise and a sustained high level of glucose during this test. This is because the pancreas is unable to deliver the insulin needed to lower the glucose in the blood. A blood glucose level of 11.1 mmol/L or more in the blood sample taken after two hours indicates diabetes.

Urine test for glucose

A simple dipstick test can detect glucose in a sample of urine. In a dipstick test, a special chemical strip is dipped into a sample of the patient's urine. Colour changes on the strip show whether there is glucose in the urine sample. Some people have kidneys that are more 'leaky' and glucose may leak into urine with a normal blood level. If a patient's urine contains any glucose a blood test should be carried out to measure the blood level of glucose to confirm, or rule out, diabetes.

Whether a fasting glucose, random glucose or HbA1c is used to test for diabetes it will generally need to be repeated as there should be evidence of two results using the same testing method to confirm diagnostic testing.

Diagnostic values

According to the World Health Organization, someone may have diabetes if they have:

• In patients without symptoms of diabetes the laboratory venous HbA1c should be repeated. If the second sample is <48mmol/mol (6.5%) the person should be treated as at high risk of diabetes and the test should be repeated in 6 months or sooner if symptoms develop (Diagnostic criteria for diabetes, Diabetes UK)
• a fasting blood glucose of 7 mmol/L or more, OR
• a blood glucose 11.1 mmol/L or more after a two-hour oral glucose tolerance test. (GTT).

Someone has impaired glucose tolerance if they have:

• a fasting blood glucose of less than 7 mmol/L, AND
• a blood glucose of 7.8 mmol/L or more but less than 11.1mmol/L after a 2-hour oral GTT (where a person is fasted and then given a quantity of glucose to observe the pancreatic response to raised blood glucose).

Someone has impaired fasting glycaemia if they have:

• a fasting blood glucose between 6.1 to 6.9 mmol/L, AND
• a blood glucose of less than 7.8 mmol/L after a two-hour oral GTT.

Useful resources

• Diabetes UK. Diagnostic criteria for diabetes

By getting the right type of diabetes diagnosed correctly, it means the appropriate treatment and care can be provided to the patient. This is not always an easy task, and only by reviewing the history, signs and symptoms alongside diagnostic tests, while remaining clinically ‘curious’, can you ensure correct diagnosis.

Type 1

• Cause: An autoimmune condition where the immune system attacks and destroys the insulin-producing beta cells in the pancreas.
• Characteristics: The body produces little to no insulin.
• Onset: Typically develops in childhood or adolescence but can occur in adults. There are stages of type 1 diabetes, it starts with the genetic predisposition, the antibodies develop and start to destroy the beta cells; however, this can go on for years before people reach type 1 diabetes.
• Management: Requires insulin injections or an insulin pump, along with regular blood glucose monitoring.

Type 2

• Cause: The body becomes resistant to insulin or doesn't produce enough insulin.
• Characteristics: Metabolic features that raise diabetes risk include insulin resistance, central obesity, dyslipidaemia, hypertension, chronic inflammation and impaired glucose regulation. Risk is elevated in certain ethnic groups and low-income populations due to socioeconomic stressors and dietary patterns, sedentary lives, and shiftwork. Genetic predisposition leading to varying fat thresholds for insulin resistance contributes to disease onset.
• Onset: More common in adults but increasing in children due to rising obesity rates.
• Management: Lifestyle changes (diet and exercise), oral medications, injectable medications (GLP1) and insulin therapy.

Gestational diabetes

• Cause: Hormonal changes during pregnancy that lead to insulin resistance.
• Characteristics: Occurs during pregnancy and usually resolves after childbirth.
• Risk: Increases the risk of developing type 2 diabetes later in life for both the mother and the child.
• Management: Often managed with diet, exercise and sometimes medication, such as metformin or insulin
• Note: It may be undiagnosed type 1/type 2 diabetes which has been found in pregnancy. Follow up is essential.

Type 3c diabetes

• Cause: Resulting from damage to the pancreas due to diseases like pancreatitis, pancreatic surgery or pancreatic cancer.
• Characteristics: Similar to type 1 and type 2 diabetes, with impaired insulin production and potential insulin resistance.
• Management and onset: Insulin therapy is often needed, along with enzyme replacement therapy if pancreatic exocrine function is compromised.

Drug-induced diabetes

• Cause: Often medications have side effects, which include the raising of blood glucose levels. Drug-induced diabetes is when use of a specific medication has led to the development of diabetes.
• Characteristics: Drugs that have been linked with an increased risk development of type 2 diabetes include corticosteroids, thiazide diuretics, beta-blockers, antipsychotics and statins.
• Onset: There is usually a slower onset of drug-induced diabetes, depending on the dose of the drug and the length of time a patient has been on a certain medication.
• Management: Where possible, aim to reduce or stop any medications linked to diabetes onset and management via a healthy lifestyle, exercise and by using oral or injectable agents where required.
  
  Diabetes UK. Drug induced diabetes

Ketosis-prone diabetes

• Cause: Ketosis-prone diabetes is a less common form of diabetes that doesn't fit neatly into the typical type 1 or type 2 categories. It usually affects individuals who appear to have type 2 diabetes but present with diabetic ketoacidosis (DKA), a condition more often associated with type 1. These individuals often have no clear trigger for the DKA episode and may not have previously been diagnosed with diabetes.
• Characteristics: The condition usually begins with very high blood glucose levels and DKA. When ketones build up in the blood, this can lead to symptoms such as a fruity smell on the breath, abdominal pain, nausea, vomiting and shortness of breath.
• Onset: The onset is typically rapid, and symptoms may develop suddenly, even in people who had previously stable blood sugar control. This often leads to an emergency hospital admission.
• Management: Initial treatment focuses on stabilisation with fluids, correction of electrolyte imbalances, and insulin therapy to bring down blood glucose levels. Longer-term care should involve specialist diabetes teams, who can reassess whether ongoing treatment requires insulin or if oral medication may be suitable after recovery.
  
  Adapted from clinical guidance and international resources, including Diabetes Africa (2023)

Type 5 Diabetes (Malnutrition-Related Diabetes)

• Overview: Type 5 diabetes, also referred to as malnutrition-related diabetes, is primarily caused by long-term undernutrition—particularly during childhood and adolescence. It is estimated to affect up to 25 million people globally, most commonly in parts of Asia and sub-Saharan Africa.
• Cause and distinction: Unlike type 2 diabetes, which is typically linked to insulin resistance and lifestyle factors, type 5 diabetes is the result of impaired pancreatic development due to chronic nutritional deficiency. This leads to reduced insulin production, but without the autoimmune damage seen in type 1 or the insulin resistance characteristic of type 2.
• Why it matters: This form of diabetes has historically been under-recognised and often misclassified as type 1 or type 2. Recent research, including work by Dr Hawkins and others, has clarified that it has a distinct physiological pattern: insulin deficiency without resistance.
• Management considerations: Some individuals with type 5 diabetes may be managed with oral medications rather than insulin, which can be especially important in low-resource settings. Tailoring treatment to the local context and available healthcare infrastructure is key.
  
  Adapted from public health literature and global diabetes research, including WHO and Diabetes Africa

What about pre-symptomatic type 1 diabetes?

This can be defined as the stage where autoantibodies are present, but no clinical symptoms have developed.

The immune system attacks the beta cells in the pancreas through a process called insulitis. This starts when HLA class II molecules present antigens, triggering T lymphocytes (CD4 and CD8) to respond.

How damage occurs

• T cells release harmful substances (for example, IL-1, TNF-α)
• T cells directly kill beta cells
• This creates a cycle of inflammation and immune attacks, gradually destroying beta cells.

The process can take years, especially in adults. Symptoms typically appear only after most beta cells have been damaged and stopped functioning.

Autoantibodies Involved (AAbs) to support diagnosis include:

• Islet cell antibodies (ICA)
• Glutamic acid decarboxylase antibodies (GADA)
• Insulin autoantibodies (IAA)
• Zinc transporter 8 antibodies (ZnT8A).

The flowchart below can help you understand what investigations are required for suspected type 1 diabetes in newly diagnosed adults.

Richard I G Holt et al. (2021) The management of type 1 diabetes in adults. A consensus report by the American Diabetes Association (ADA) and the European Association for the Study of Diabetes (EASD) , Diabetologia, 2021 Dec; 64(12): 2609–2652. This report can be used alongside the flowchart to help identify the stages of type 1 diabetes to support diagnosis, as getting it right first time is important to ensure correct treatment is started.   

Further resources

• Diabetes Research (2021). Progress towards prevention of type 1 diabetes: Teplizumab
• TrialNet. Type 1 Diabetes Pathway to Prevention
• BR1DGE. BR1DGE provides expert-led educational content on the latest understanding in autoimmune type 1 diabetes (T1D).