Diabetes diagnosis

Who To Test for Diabetes?

Consider a diagnosis of diabetes in a person with potential symptoms of diabetes:

• thirst and polyuria
• unexplained weight loss or tiredness
• pruritus vulvae, balanitis or recurrent ‘UTIs’
• recurrent infections
• blurring of vision (usually an osmotic effect and not permanent)

Asymptomatic individuals at high risk of diabetes may also be screened:

• hypertension, cardiovascular disease
• obesity, especially if: BMI ≥30 kg/m², high risk ethnic group, family history of Type 2 diabetes and/or learning disability
• long-term anti-psychotic medication, e.g. olanzapine, clozapine
• PCOS (should have annual check of HbA1c)
• previous gestational diabetes (should have annual check of HbA1c)
• pre-diabetes (should have an annual check of HbA1c)

Diagnostic Criteria

In those with severe symptoms of diabetes, those who are unwell or have positive blood or urine ketones, who may need immediate insulin treatment, finger prick glucose and ketones are sufficient prior to immediate referral via bleep #6698 or medical registrar.

 

Diabetes and pre-diabetes may be diagnosed by any of the following criteria:

	Diabetes	Pre-Diabetes	Normal
HbA1c (mmol/mol)	≥48	42-47	≥41
Fasting glucose (mmol/l)	≥7.0	5.5-6.9	≥5.4
2-hr glucose in OGTT (mmol/l)	≥11.1	7.8-11.0	≥7.7
Random glucose (mmol/l)	≥11.1

 

In individuals with symptoms of diabetes, only one blood test is required.

OGTTs are almost never required out with pregnancy.

 

In individuals with a blood test diagnostic of diabetes, a repeat confirmatory test is required in those who are asymptomatic. There is no minimum time limit as to when the repeat needs to be carried out and best practice is that it should be undertaken within 2 weeks. Best practice in people with a new diagnosis of pre-diabetes is that a repeat confirmatory test should also be carried out if the result is significantly different from a previous HbA1c result or out of keeping with the clinical picture. Guidance on the management of pre-diabetes is available on RefHelp.

 

When Might HbA1c Not Be Reliable?

HbA1c may not be reliable in people who have has a blood transfusion within the last three months, those with untreated B12 or iron deficiency, those with a haemoglobinopathy, those with states of reduced red cell survival (haemolytic anaemia, splenomegaly or on antiretroviral drugs) or those on renal dialysis. In these cases fasting blood glucose is a better test for diabetes diagnosis.

HbA1c is also not suitable for people who have rapid onset of diabetes symptoms or in pregnant women where it may be falsely reassuring.

 

Ketone Testing

It is strongly recommended that a urine or point of care (POC) finger-prick capillary blood sample is checked for ketones in all symptomatic people with suspected diabetes and in asymptomatic individuals subsequently diagnosed with diabetes.

 

Blood ketone testing is a good alternative to urine ketone testing, particularly in dehydrated individuals who may struggle to provide a urine sample. It provides an immediate measure of ketone status from a capillary sample of blood. With increasing use of SGLT2 inhibitors for Type 2 diabetes, which are associated with a risk of euglycaemic ketoacidosis during intercurrent illness, we suggest that practices should consider getting a blood ketone meter/test strips for the assessment of unwell individuals on these agents. If blood ketone measurement is not available then please dip urine (++ or +++ is significant ketonuria).

Ketonaemia can clearly be an indicator of diabetic ketoacidosis, or incipient ketoacidosis. However, low level ketonaemia can be found in individuals who are fasting or who are following a low carbohydrate diet. Below is a guide for interpretation of blood ketones in someone with a new diagnosis of diabetes.

 

Blood Ketones	Interpretation / Action
<0.6 mmol/l	Normal
0.6-1.5 mmol/l	Possible incipient DKS. Phone on-call diabetes team
>1.5 mmol/l	High probability of DKA, Admit immediately to hospital if unwell. Otherwise phone on-call diabetes team.

 

Types of Diabetes

Diabetes mellitus has many different causes. It is very important that the full potential differential diagnosis is considered in all new presentations of diabetes. 

Type 1 Diabetes

This results from an absolute deficiency of insulin due to autoimmune pancreatic beta-cell destruction. It more commonly presents acutely in young people, but can occur at any age.  A history of significant weight loss prior to diagnosis and the presence of ketones in the urine or blood are highly suggestive of type 1 diabetes. People with type 1 diabetes usually have detectable antibodies to GAD, IA-2 and/or ZnT8. Type 1 diabetes can occur in any individual regardless of age, ethnicity or weight. Therefore, measurement of blood or urine ketones should be performed in ALL individuals with a new diagnosis of diabetes. Patients thought to have a new diagnosis of type 1 diabetes must be referred to same day to the diabetes consultant on page 6698, or via the medical registrar oncall. Please do not use email to refer these patients due to urgency.

Type 2 Diabetes

This results from a relative deficiency of and/or insensitivity to insulin and is more commonly diagnosed in older people, although can occur in young (especially obese) individuals. It is also more common in people of South-Asian and Afro-Caribbean heritage.

Although the onset of type 2 diabetes is less dramatic than that of type 1 diabetes, the long-term sequelae are similar and equally devastating, as both Type 1 and Type 2 patients are at risk of developing the microvascular and macrovascular complications of the disease. 

Pancreatic Diabetes (Type 3c diabetes)

Diabetes may be caused by disorders of the pancreas such as chronic pancreatitis, haemochromatosis, cystic fibrosis, pancreatic cancer and post-pancreatic surgery. The diagnosis of these forms of diabetes may be obvious depending on previous history, but these forms of diabetes should be considered in all individuals whose presenting features are not typical of type 1 or type 2 diabetes.

Steroid-Induced Diabetes

High doses of steroids, such as prednisolone or dexamethasone, can induce diabetes in susceptible individuals, i.e. older age and overweight. Individuals with an HbA1c in the pre-diabetic range (42-47 mmol/mol) are highly likely to develop diabetes if commenced on steroids. It is recommended that all patients going onto long term steroids equivalent to prednisolone 10mg/day should have a HbA1c and be warned of the symptoms of diabetes. If in the diabetes or pre-diabetes range then early commencement of blood glucose monitoring is recommended (see Steroid Safety guidance on RefHelp).

Monogenic Diabetes

These are rare forms of diabetes due to mutations in single genes; they are inherited in an autosomal dominant fashion. There are multiple different forms and the management principles depend on the specific gene involved. A diagnosis of monogenic diabetes should be suspect in individuals who do not demonstrate typical features of type 1 or type 2 diabetes. Further information about these forms of diabetes can be found at www.diabetesgenes.org

 

Pre-Diabetic States

 

Impaired Fasting Glycaemia (IFG)

The term IFG classifies individuals with fasting plasma glucose (FPG) values above the normal range but below those diagnostic of diabetes i.e. FPG 6.1 mmol/L – 6.9mmol/L.   All such individuals should have a HbA1c checked to exclude a diagnosis of diabetes (see diagnosis of diabetes in asymptomatic individuals)

 

Impaired Glucose Tolerance (IGT)

This will be rarely diagnosed as OGTT is no longer advised as first line test for diabetes out with pregnancy. IGT is a state of impaired glucose regulation, diagnosed on glucose tolerance testing, which confers an increased risk of future diabetes of 2-5% per year.  Patients with IGT tend to have higher blood pressure and plasma triglycerides when compared to non-diabetic individuals.

 

Pre-diabetes

HbA1c between 42-47 is considered a pre-diabetic state.

All pre-diabetic states are risk categories for future development of type 2 diabetes or cardiovascular disease. These individuals should have an annual HbA1c check to screen for diabetes. Life style factors should be addressed and co-existing cardiovscular risk factors treated aggressively. Further information can be found on the Pre-Diabetes Refhelp page.

 

Gestational Diabetes Mellitus (GDM)

GDM is defined as carbohydrate intolerance of variable severity with onset or first recognition during pregnancy. GDM is still mainly diagnosed using an oral glucose tolerance test (OGTT) and this is essentially the only situation now when an OGTT should be performed in primary care. The diagnostic criteria are different to that for standard diabetes: fasting glucose ≥ 5.3 mmol/l and 2hr glucose ≥9.0 mmol/l.

Women with risk factors for GDM, e.g. family history of type 2 diabetes, high risk ethnic group, previous large baby, elevated BMI, PCOS and age above 35  will have an OGTT arranged by their community midwife at 24-28 weeks and referred to the combined diabetes obstetric clinic if positive.

Women with a history of GDM have a 60% chance of developing type 2 diabetes over the next 20 years. HbA1c should be checked annually and lifestyle factors should be addressed.