Laboratory parameters of the 1st order – obligatory laboratory tests.
- Glucose (blood glucose; each measured in blood plasma, venous) [To confirm diagnosis, a defined elevated blood glucose value must be present at least twice]
- Fasting glucose (fasting blood glucose; fasting plasma glucose) ≥ 126 mg/dl (7 mmol/l)
- Glucose measurement at any time/occasional blood glucose (“random plasma glucose”) [≥ 200 mg/dl (11.1 mmol/l) and typical symptoms such as polydipsia/diseased increased thirst, polyuria/diseased increased urine output, etc.].
- Blood glucose daily profile
- OGTT test [≥ 11.1 mmol/l 2hours after oral administration of 75 g glucose]
- HbA1c level [> 6.5 %]
- Small blood count [e.g. E.g., Hk↑ due to dehydration (lack of fluid) and hyperglycemia (hyperglycemia) in coma diabeticum; exclusion of leukocytosis (increase in white blood cell count)/infection]
- Electrolytes – potassium, sodium
- Blood gas analysis (ABG) – if diabetic ketoacidosis is suspected; in circa 25% of cases, ketoacidotic coma is the first sign of type 1 diabetes mellitus.
- Albumin, glucose and ketone bodies (in urine).
- Uric acid – high-normal serum uric acid levels appear to be an early warning sign of diabetic kidney damage (indicative of renal loss of function); may be present in type 1 diabetics at a time when albuminuria is not yet present!
Laboratory parameters 2nd order – depending on the results of the history, physical examination, etc. – for differential diagnostic clarification.
- Autoimmune diagnostics in diabetes mellitus:
- Autoantibodies to insulin (insulin-Ak; insulin autoantibodies (IAA)) [diabetes mellitus type 1a; approximately 90% of cases]
- Anti-glutamic acid decarboxylase antibody/anti-glutamate decarboxylase autoantibody (anti-GAD65-Ak).
- Anti-tyrosine phosphatase antibody/autoantibody to protein tyrosine phosphatase IA 2 (IA-2-Ak), an islet cell antigen (anti-IA 2).
Diabetes-type autoantibodies can detect diabetes mellitus type 1 months to years before its onset (thus suitable for screening; thus also avoids ketoacidosis) [marker of β-cell destruction]Note: In young slender patients (< 25 years) with positive family history of diabetes, who are antibody negative, think of MODY diabetes. It is also typically characterized by an insidious onset of the disease and no occurrence of ketoacidosis.
- TSH and TPO antibody screening – in children and adolescents with type 1 diabetes at the time of diagnosis due tocomorbidity (concomitant disease) autoimmune thyroiditis.
- Transglutaminase antibody (tTG) or endomysium antibody (EMA)/ endomysium IgA and transglutaminase IgA – if celiac disease is suspected (every 1-2 years due topossible comorbidity).
- Urea, creatinine, creatinine clearance if necessary.
- Insulin
- C-peptide (part of proinsulin) – in suspected insulinoma, DD of hypoglycemia (hypoglycaemia factitia).
- Insulin receptor AK (in insulin resistance); insulin auto-AK (IAA), HLA-DR3 and -DR4.
- Proteinuria differentiation
- Anti-pancreatic islet cells (ICA), GAD-II-AK, IA-2-AK.
- Lp-PLA2 (vascular inflammatory enzyme lipoprotein-associated phospholipase A2; inflammatory marker) – for risk stratification of cardiovascular disease.
Family screening
- Prediabetic diagnosis in at-risk groups – screening of first-degree relatives: testing of children from 2-3 years of age; second testing if negative at approximately 10 years of age [IA-2-Ak].
