Javascript DHTML Drop Down Menu Powered by
Diabetes - Classification and Diagnosis

Diabetes - Classification and Diagnosis

Section Bullet



The World Health Organisation (WHO) updated their classification and diagnostic criteria of Diabetes Mellitus in 2006 and published guidance on the use of HbA1c in diagnosis in 2011.


At present the local position is that the glucose criteria should be used for diagnosis and that HbA1c should be restricted to the surveillance of those with demonstrated Impaired Glucose tolerance or Impaired Fasting Glucose.


Diagnostic criteria:

Requires 1 abnormal glucose if symptomatic, and 2 abnormal glucose if asymptomatic.



Diabetes Mellitus



Fasting venous plasma glucose

≥ 7.0



Random or 2hr post glucose load

≥ 11.1

or both


Impaired Glucose Tolerance (IGT)


Fasting (if measured)

< 7.0




≥7.8 and ≤ 11.0


Impaired Fasting Glucose (IFG)



≥ 6.1 and <7.0


2hr (if measured)

< 7.8


Use laboratory plasma glucose for diagnosis, however in urgent cases (eg newly diagnosed type 1) treatment and management should not be delayed until laboratory confirmation.

Oral Glucose Tolerance Test (OGTT) is not usually required, but may be used if fasting blood glucose levels are equivocal and non-diagnostic. (see -the OGTT flowchart and OGTT protocol in Useful Resources and Links section ). OGTT is used routinely in diagnosis of gestational diabetes.

Urinalysis for glucose should not be used in diagnosis nor screening of diabetes

Section Separator

Section Bullet



Type 1 diabetes- usually obvious. Acute onset of hyperglycaemic symptoms usually in young person or child, although 10% can be in age >65. Often presents with weight loss, and associated with ketonuria and raised random blood glucose.


Type 1 diabetes can occur at any age, although most common in childhood and young adults.


Type 2 diabetes- more insidious (see - Early Detection and Screening). Most are overweight or obese. Often asymptomatic although direct questioning may reveal long standing hyperglycaemic symptoms. Some may present with complications (vascular disease, painful neuropathy, diabetic retinopathy, foot ulcer). Weight loss is unusual, and should trigger consideration for early insulin therapy (see - Management of Newly Diagnosed Diabetes).


Both type 1 and rarely type 2 patients can present late in Diabetic KetoAcidosis (DKA), and type 2 patients in Hyperosmolar, Hyperglycaemic State (HHS). These are medical emergencies and require urgent hospital treatment.


Hyperglycaemic symptoms:

Thirst, dry mouth, polydipsia

Polyuria, nocturia

Urinary and genital infections (fungal or bacterial)

General fatigue, lassitude.

Section Separator

Section Bullet

Classification of Diabetes Mellitus



Type 1

β -cell destruction, usually leading to absolute insulin deficiency





Type 2

May range from predominantly insulin resistance with relative insulin deficiency to a predominantly secretory defect with or without insulin resistance



Other specific types

Genetic defects  of β- cell function

Genetic defects in insulin action

Diseases of the exocrine pancreas


Drug or chemical-induced


Uncommon forms of immune-mediated diabetes

Other genetic syndromes



Gestational diabetes
(see - Diabetes in Pregnancy).

Section Separator

Section Bullet

Impaired Glucose Tolerance  (IGT) and Impaired Fasting Glucose (IFG)


Impaired Glucose Tolerance


  Fasting (if measured) < 7.0 and
2hr ≥7.8 and ≤ 11.0  
  Impaired Fasting Glucose    
  Fasting ≥ 6.1 and <7.0 and
2hr (if measured) < 7.8

IGT is associated with increased cardiovascular risk


IFG is associated with increased risk of future diabetes


Subjects with IFG diagnosed on fasting glucose alone, ideally should have a full OGTT to exclude diabetes


OGTT should be performed on usual diet. Acute carbohydrate restriction prior to OGTT may lead to erroneous results.


Both IGT and IFG subjects should be given lifestyle advice on weight control, diet and exercise (See - Nutritional Information)


Both IGT and IFG subjects should be offered regular surveillance for early detection of type 2 diabetes (See - Early Detection & Screening) HbAic may be appropriate for this rather than repeating the OGTT.


Structured education "Walking Away from Diabetes" is available for patients registered with Luton GP  (See - Structured Diabetes Education)


Section Separator

Section Bullet

OGTT (Oral Glucose Tolerance Test)


To book OGTT

> Bedford   > Luton

Bedford Hospital: Glucose Tolerance tests are performed in the Phlebotomy Department at 09.00 hrs by appointment only. Please telephone extension 2458 to arrange.

(See -  OGTT protocol for full instructions, including patient preparation.)

Section Separator

Section Bullet

Useful External Links & Resources

PDF File

Luton Community Diabetes Referral Form

PDF File

Instructions for Oral Glucose Tolerance Test

PDF File

GP Referred GTT Information Sheet
Section Separator

You may need Adobe Acrobat Reader to view these documents. If you do not have this installed, you can download it free from Adobe's website

  Get Acrobat
  Javascript DHTML Drop Down Menu Powered by
  2010-14  - Diabetes Guidelines  -   Home | Privacy | Terms of Use | Sponsors  | Editors