Diagnosing diabetes

Check CBG on everyone admitted, diabetic or not (hyperglycaemia is often not noted on a VBG if patient not known to be diabetic – look for it)
Risk of DM can be calculated – need to know demographics, family history, waist circumference, BMI, history of HTN
Typical symptoms include polydipsia, polyuria, blurred vision, weight loss, recurrent infections, fatigue. But can be absent.
Ask about
- - Family history of DM and autoimmune disorders
  - Previous gestational DM
  - Medications (in case causative)
  - Any other symptoms (which may suggest an atypical cause, such as endocrine)
Examine for
- - Skin – Striae (cushings), acanthosis nigricans (insulin resistance), necrobiosis lipidoica (see other diabetic complications)
  - Features of endocrine or pancreatic disease
  - Complications of DM – feet, peripheral nerves, eyes

Any of
- - Fasting blood glucose > 7
  - Or HbA1c >48
  - Or random glucose > 11 + symptoms
If no symptoms – check blood sugar (not CBG) on two occasions, and/or HbA1c (but see below)
If repeat CBG normal – monitor (transient hyperglycaemia can be caused by infection, trauma, other stresses)
Oral glucose tolerance test – Generally only performed in pregnancy now (any degree of glucose intolerance in pregnancy is gestational DM)

Not the whole story – hides glycaemic variability
Do not use to diagnose DM if:
- - Pregnant
  - Symptoms of DM < 2 months
  - Acutely unwell
  - On drugs that cause hyperglycaemia
  - Pancreatic disease
  - End stage renal disease
  - HIV
Interpret with caution if haemoglobinopathy, severe anaemia, splenectomy, recent blood transfusion
HbA1c in anaemia
- - Normochromic anaemia secondary to CKD and haemolysis lead to falsely low HbA1c
  - Iron Deficient Anaemia (IDA) and B12/folate deficiency falsely elevate HbA1c
Cause of falsely elevated HbA1c
- - Uraemia
  - Acidosis
  - IDA
  - B12 or folate deficiency
  - Splenectomy
  - Untreated hypothyroidism
  - Severe hypertriglyceridaemia
  - Haemoglobin variants
Causes of falsely low HbA1c
- - Blood loss
  - Blood transfusions
  - Haemolysis
  - Anaemia and haemoglobinopathies
  - EPO treatment
  - Drugs (sulphasalazine, dapsone, ARVs)
  - G6PD deficiency
  - Splenomegaly
  - Advanced CKD
  - Pregnancy
  - Liver disease
If HbA1C > 48, patient probably has DM – manage accordingly (but not valid for T1DM which starts acutely).
42-48 – probably pre-diabetes
Target HbA1C depends upon the patient
Suspect falsely low HbA1C if discordant with history or if consistently high CBGs. You can get a 7-day glucose sensor from a diabetes clinic in this instance

Diagnosing Type 1 DM

Often (but not always): ketosis, rapid weight loss / BMI < 25, aged <50, personal/family of autoimmunity
Antibodies and c-peptide are not routine to conform diagnosis
- - Indicated if aged > 50, BMI >25, slowly evolving hyperglycaemia, suspected monogenic DM, DM type uncertain
  - In practice almost always done in suspected new T1DM
Antibodies
- - GAD (antiglutamic decarboxylase autoantibodies) – 70% positive at diagnosis
  - ICA (anti-islet cell autoantibodies) – present in 90% of T1DM
  - ZnT8 (zinc transporter) – 55% present at diagnosis
  - IA-2 – 55% positive at diagnosis, and higher in kids
  - Absence of antibodies does not rule out T1DM
  - False negative rate increases as time from diagnosis increases
C-peptide levels tend to be low / reduced in new type 1 DM (normal or high in type 2)
Screen for pancreatic cancer if there is new onset type 2 diabetes in older people with dramatic weight loss and features of exocrine insufficiency / risk factors
Kit to consider on discharge after new diagnosis of T1DM
- - Insulin pens and needles, sharps box
  - CBG and ketone meters
  - Test strips & lancets for both
  - Glucose gel +/- glucagon 1mg IM injection
  - Insulin passport, medic alert bracelet or diabetes card