Approach
Clinical presentation
Type 1 diabetes can be diagnosed at any age, with a peak around 10 to 14 years.[13]
In children and young people aged under 18 years of age, the signs of type 1 diabetes include:[35]
Hyperglycaemia (random plasma glucose ≥11.1 mmol/L [≥200 mg/dL])
Polyuria
Polydipsia
Weight loss
Excessive tiredness.
Other symptoms such as blurred vision may occur.[36]
Adults with type 1 diabetes typically present with hyperglycaemia and usually (but not always) one or more of:[37]
Ketosis
Rapid weight loss
Age <50 years
BMI <25 kg/m²
Personal and/or family history of autoimmune disease.
Rarely, an adult patient is diagnosed with type 1 diabetes during routine blood tests. The condition is diagnosed long before its chronic complications have developed.
Many patients present with diabetic ketoacidosis, an acute complication of type 1 diabetes.[38][39] These patients have symptoms of dehydration and acidosis such as nausea, vomiting, abdominal pain, tachypnoea, tachycardia, and lethargy. See our topic Diabetic Ketoacidosis.
There is also a slow-progressing form of autoimmune diabetes known as latent autoimmune diabetes in adults (LADA).[2] The patient with LADA may not require insulin treatment for some years and it can therefore be mistaken for type 2 diabetes in the early stages.[2] Features that suggest the presence of LADA rather than type 2 diabetes include two or more of the following: age of onset <50 years, acute symptoms, body mass index less than 25 kg/m², and personal or family history of autoimmune disease.[4]
Diagnosis in children
Suspect diabetes in children and young people under 18 years of age using the World Health Organization (WHO) criteria:[35][1]
In a symptomatic patient, random plasma glucose of ≥11.1 mmol/L (≥200 mg/dL) or
Fasting plasma glucose ≥7.0 mmol/L (≥126 mg/dL) or
Plasma glucose ≥11.1 mmol/L (≥200 mg/dL) 2 hours after 75 g oral glucose or
Glycosylated haemoglobin (HbA1c) ≥6.5% (≥48 mmol/mol).
Bear in mind that a repeat confirmatory test is required in most cases.
If you suspect the child has type 1 diabetes refer immediately (on the same day) to a multidisciplinary paediatric diabetes team who can confirm the diagnosis and give immediate care.[35]
Assume type 1 diabetes in children and young people unless there are strong indications of type 2 diabetes, monogenic or mitochondrial diabetes.[35] See our topic Type 2 diabetes in children.
Consider type 2 diabetes in a child or young person with suspected diabetes who:[35]
Has a strong family history of type 2 diabetes
Is obese at presentation
Is of black or Asian family origin
Has no insulin requirement, or has an insulin requirement of less than 0.5 units/kg body weight/day after the partial remission phase
Shows evidence of insulin resistance (for example, acanthosis nigricans).
Consider other types of diabetes (i.e., not type 1 or 2) in a child or young person with suspected diabetes who has any of the following features:[35]
Diabetes in the first year of life
Ketonaemia during episodes of hyperglycaemia
Associated features, such as optic atrophy, retinitis pigmentosa, deafness, or another systemic illness or syndrome.
Monogenic diabetes accounts for up to 4% of paediatric diabetes and insulin treatment is inappropriate in these cases.[40] The two main forms of monogenic diabetes are maturity-onset diabetes of the young (MODY) and neonatal diabetes mellitus (NDM). In NDM, diabetes is diagnosed in the first 6 months of life and may be transient (resolution by 12 months of age) or permanent. More than 90% of cases of permanent neonatal diabetes mellitus are caused by a KCNJ11 or ABCC8 genetic change which affects the link between sensing of glucose levels and release of insulin from the pancreatic β-cell.[41] Genetic testing is definitive and can be used to counsel the patient and family members.
Do not routinely measure C-peptide and/or diabetes-specific autoantibody titres at initial presentation to distinguish type 1 diabetes from type 2 diabetes. The National Institute for Health and Care Excellence (NICE) in the UK recommends only considering measuring C-peptide if there is difficulty distinguishing type 1 diabetes from other types.[35]
If C-peptide testing is indicated, bear in mind that it has better discriminative value the longer the test is done after initial presentation.[35]
In clinical practice, C-peptide testing should only be done with a paired glucose. In practical terms, this can be achieved by using C-peptide on a single non-fasting random blood or urine sample after the patient has eaten one of their own meals.[42] Otherwise, C-peptide might be suppressed, making a false positive result more likely. This is a particular concern if the patient has been started on therapy that can cause hypoglycaemia (e.g., insulin).
See Monitoring section for information on initial screening tests and ongoing monitoring in children with type 1 diabetes.
Diagnosis in adults
NICE recommends diagnosing type 1 diabetes on clinical grounds if an adult patient presents with hyperglycaemia, bearing in mind the typical features of clinical presentation detailed above.[37]
Do not discount a diagnosis of type 1 diabetes if the patient has a BMI >25 kg/m² or is aged over 50 years.[37]
On diagnosis, immediately refer the patient to the local eye screening service.[37] Screening must be performed:[37]
As soon as possible and no later than 3 months from initial referral
Every year thereafter.
See Monitoring section for more information on initial screening tests and ongoing monitoring in adults with type 1 diabetes.
Do not routinely measure C-peptide and/or diabetes-specific autoantibody titres to confirm type 1 diabetes in adults. NICE recommends only considering these tests if:[37]
You suspect type 1 diabetes but the presentation includes atypical features (e.g., age >50 years, BMI >25 kg/m², slow evolution of hyperglycaemia or long prodrome)
Type 1 diabetes has been diagnosed and treatment started but you have a clinical suspicion that the person may have a monogenic form of diabetes, and C-peptide and/or autoantibody testing may guide the use of genetic testing
Classification is uncertain, and confirming type 1 diabetes would have implications for availability of therapy (for example, continuous subcutaneous insulin infusion [CSII or 'insulin pump'] therapy).
When C-peptide and/or diabetes-specific autoantibody titres are indicated, bear in mind that:[37]
Autoantibody tests have their lowest false negative rate at the time of diagnosis; the false negative rate rises thereafter
C-peptide has better discriminative value the longer the test is done after diagnosis
With autoantibody testing, carrying out tests for two different diabetes-specific autoantibodies, with at least one being positive, reduces the false negative rate
In clinical practice, C-peptide testing should only be done with a paired glucose. In practical terms, this can be achieved by using C-peptide on a single non-fasting random blood or urine sample after the patient has eaten one of their own meals.[42] Otherwise, C-peptide might be suppressed, making a false positive result more likely. This is a particular concern if the patient has been started on therapy that can cause hypoglycaemia (e.g., insulin).
Advice to adults with type 1 diabetes should be co-ordinated between a multidisciplinary team with skills in diabetes care.[37]
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