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Primary Care Hacks

The Diagnosis and Classification of Diabetes in Primary Care

Guidelines presents Primary Care Hacks, a series of clinical aide-memoires across a range of topics. Developed by Dr Kevin Fernando, Primary Care Hacks aim to provide a quick and easy resource for primary healthcare professionals and ultimately help improve patients' lives.

Take a Look at Medscape UK's other Primary Care Hacks

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The Diagnosis and Classification of Diabetes in Primary Care

Latest Update

November 2023: Pancreatic cancer diagnosis in type 3c diabetes updated to include recommendation from the Scottish referral guidelines for suspected cancer; useful resources added to provide information on steroid-induced diabetes.

Type 1 and type 2 diabetes are the most commonly encountered types of diabetes in primary care, but there are a number other forms of diabetes that healthcare professionals need to be aware of. It is increasingly challenging to differentiate between types of diabetes in primary care; this Primary Care Hack summarises the diagnosis and classification of several different types of diabetes and offers diagnostic tips, as well as pitfalls to avoid when diagnosing diabetes in primary care.

Click on the link below for a downloadable PDF of the Primary Care Hack

The Diagnosis and Classification of Diabetes in Primary Care

Expand the table below for full view.

 T1DLADAT2DMonogenic DiabetesGDMT3cD (Pancreatogenic)


Autoimmune destruction of pancreatic beta cells

Clinical diagnosis ± PG and ketone levels. Urgent specialist discussion required

It is increasingly challenging to differentiate T1D from T2D, partly due to the obesity epidemic. Often the safest strategy is to presume T1D until proven otherwise

LADA is essentially ‘slow-onset’ T1D

Gradual autoimmune

destruction of pancreatic beta cells. Diagnosis and management similar to T1D

See Diabetes UK’s Latent autoimmune diabetes in adults

IR with relative insulin deficiency

T2D is usually diagnosed when HbA1c ≥48 mmol/mol. If use of HbA1c is inappropriate (e.g. pregnant women, genetic variants [HbS or HbC trait], acute or chronic blood loss, end-stage kidney disease) then T2D is diagnosed by an FPG ≥7 mmol/l

If asymptomatic, the diagnosis should never be based on a single abnormal HbA1c or PG level; at least one additional abnormal test is essential

Genetic mutation leading to diabetes. Most common is MODY

See for diagnosis guidance

Impaired glucose tolerance in pregnancy due to pancreatic beta-cell dysfunction on background of IR

NICE NG3[1] diagnostic criteria: FPG ≥5.6 mmol/l or 2-hour PG post 75 g OGTT ≥7.8 mmol/l, i.e. much lower than the diagnostic criteria for non-pregnant individuals

Some areas use FPG levels ≥5.1 mmol/l, as any degree of hyperglycaemia in pregnancy increases the risk of both adverse fetal and maternal outcomes

Diabetes associated with disease, trauma or surgery of the exocrine pancreas

Causes include acute and chronic pancreatitis, pancreatic surgery, cystic fibrosis, haemochromatosis and pancreatic cancer

See Pancreatic Cancer Action’s information on T3cD

Often misdiagnosed as T2D

Age at Diagnosis

Usually <25 years but can occur at any age

Can occur at any adult age

Often initially mistaken for T2D

Both adults and children at any ageMODY onset often during 2nd to 5th decades and usually <45 years

Can occur in any women of child-bearing age

Women with GDM have a nearly 10-fold higher risk of developing TD2[2]

Follow up after delivery: women require lifelong annual HbA1c (NICE NG3)[1]

Both adults and children at any age

Exclude pancreatic cancer in those >60 years (NICE NG12)[3] or >55 years (Scottish referral guidelines for suspected cancer)[4] with new-onset diabetes and unexplained 
weight loss

Weight at DiagnosisUsually underweight but occur at any weight

Marked weight loss common


Usually overweight


RF for GDM include overweight/obesity but baseline weight can be variable


Family History of Diabetes

Infrequent (5–10%)


Frequent (75–90%)



Strong FH of diabetes (any type) involving two or three consecutive generations may point towards a diagnosis of MODY

FH of diabetes is an important RF for GDM


Haemochromatosis and CF are AR

History of Autoimmune Disease

Often personal or FH, e.g. thyroid and coeliac disease





Variable but often PEI present, e.g. diarrhoea and steatorrhoea, abdominal discomfort, flatulence and bloating

Check stool sample for faecal elastase-1. Low levels suggestive of PEI

Pancreatic Autoantibodies







C-peptide Levels

Low/absentInitially normal then low/absentNormal to high


Normal to high


Insulin Sensitivity

Normal when treatedNormal when treated


Normal (maybe reduced if obese)


Compensatory increase in peripheral insulin sensitivity

Insulin Requirements

Immediate; specialist input urgently requiredImmediate; specialist input urgently required





Much more likely to need insulin within 5 years of diagnosis

Risk of DKA


Low initially but high once insulin-deficient

Low but euglycaemic DKA is a rare side-effect of SGLT2i

See the Guidelines Primary Care Hack, What Next After Metformin?



Low but hypoglycaemia is common and can be prolonged
Commonly Used Drugs That Can Induce Hyperglycaemia or Cause Diabetes
  • Corticosteroids e.g. prednisolone, dexamethasone (see Useful Resources)
  • Thiazide diuretics e.g. bendroflumethiazide, indapamide
  • Beta-blockers e.g. atenolol, propranolol
  • Antipsychotics e.g. olanzapine, quetiapine, risperidone
  • Statins (especially higher potency statins).
Useful Resources
Table based on Summaries of Product Characteristics and the author’s clinical experience and appraisal of the literature.

AD=autosomal dominant; AR=autosomal recessive; CF=cystic fibrosis; DKA=diabetic ketoacidosis; FH=family history; FPG=fasting plasma glucose; GDM=gestational diabetes mellitus; HbA1c=haemoglobin A1c; HbC=haemoglobin C; HbS=haemoglobin S; IR=insulin resistance; LADA=latent autoimmune diabetes in adults; MODY=maturity onset diabetes of the young; NG=NICE Guideline; OGTT=oral glucose tolerance test; PEI=pancreatic exocrine insufficiency; PG=plasma glucose; RF=risk factor(s); SGLT2i=sodium-glucose cotransporter-2 inhibitors; T1D=type 1 diabetes; T2D=type 2 diabetes; T3cD=type 3c diabetes.

This Primary Care Hack was developed by Dr Kevin Fernando, GP Partner, North Berwick Health Centre; GP with special interest in CVRM and medical education; Content Advisor for Medscape UK and Medscape Global. Primary Care Hacks are for information for primary healthcare professionals in the UK only. They bring together currently available recommendations and/or prescribing information and indications for therapeutics licensed within Great Britain. Licensed indications and/or prescribing information for Northern Ireland may differ. You are advised to review local licensed indications before prescribing any therapeutic. Primary Care Hacks are reviewed intermittently to ensure the information is up to date at the time of publication. Primary Care Hacks are independently produced by WebMD, LLC and have not been created in conjunction with any guideline or prescribing body.