Diabetes mellitus (type 1): diagnosis
The symptoms and signs in a new diagnosis of type 1 diabetes mellitus (T1DM) are typically those seen in diabetic ketoacidosis although the diagnosis is usually over a longer time frame.
Features of diabetic ketoacidosis (DKA)
- abdominal pain
- polyuria, polydipsia, dehydration
- Kussmaul respiration (deep hyperventilation)
- acetone-smelling breath ('pear drops' smell)
Investigations
- urine should be dipped for glucose and ketones
- fasting glucose and random glucose (see below for diagnostic thresholds)
- HbA1c is not as useful for patients with a possible or suspected diagnosis of T1DM as it may not accurately reflect a recent rapid rise in serum glucose
- C-peptide levels are typically low in patients with T1DM
- diabetes-specific autoantibodies are useful to distinguish between type 1 and type 2 diabetes (see below)
| Antibody |
Notes |
| Antibodies to glutamic acid decarboxylase (anti-GAD) |
Present in around 80% of patients with T1DM |
| Islet cell antibodies (ICA, against cytoplasmic proteins in the beta cell) |
Present in around 70-80% of patients with T1DM |
| Insulin autoantibodies (IAA) |
Presence in T1DM correlates strongly with age, found in over 90% of young children with T1DM but only 60% of older patients |
| Insulinoma-associated-2 autoantibodies (IA-2A) |
|
Diagnostic criteria for type 1 diabetes mellitus
If the patient is symptomatic:
- fasting glucose greater than or equal to 7.0 mmol/l
- random glucose greater than or equal to 11.1 mmol/l (or after 75g oral glucose tolerance test)
If the patient is asymptomatic the above criteria apply but must be demonstrated on two separate occasions.
Distinguishing between type 1 and type 2 diabetes meliitus